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Chapter 8-The Cell Cycle
Cell Division in prokaryotes vs. eukaryotes
prokaryotes: simply divide in two through binary fission
eukaryotes: divide into also, but through the cell cycle
-cell cycle: complex series of 5 stages that eukaryotic cells go through to divide
the importance of the cell cycle
-unicellular eukaryotes:
-to reproduce
-asexual reproduction
-binary fission
- multicellular:
-growth
-repair
-replacement
-usually develop from a single fertilized egg cell
-human cells have 46 chromosomes
- organism’s cells dividing into many cells  its surface area can keep up with its growing volume
-the timing of cell division is important
-cells in developing tissues pass through the phases of the cell cycle at various rates
-allows cells to make identical copies
-cell division needs accurate replication and equal division of the cell’s DNA
-each new daughter cell must get an identical set of chromosomes
-an error in DNA replication or cell division can lead to birth defects, cancer, and other serious diseases
-scientists have gained much of what they know about the cell cycle from studies of yeast cells
The Stages of the Cell Cycle
-as a cell completes the cycle, it becomes two new daughter cells
-when a cell divides, its nuclear membrane breaks down
-the individual chromosomes separate and become visible as they are distributed to the daughter cells
-after cytokinesis, each daughter cell enters G1 where they either commit to the full cell cycle or stay in
G0
-different types of cells spend widely different amounts of time in each phase
-when a cell in G0 or G1 gets these signals they pass through the restriction point, R
-this “point of no return” commits the cell to a full round of the cell cycle
-once the cell passes R, it can’t return to G1 or G0 without completing a full cell cycle
-cell size affects the cell cycle a lot
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2 main stages:
-interphase: the period between division
-the individual chromosomes are not visible in the nucleus
-3 stages:
1. G1: gap 1 or prereplication
-the cell grows:
-makes more cytoplasm
-increases in size
-as the cell grows larger, the surface area to volume ratio gets smaller
-either prepare for the next change or carry out the cell’s special function
2. S phase: DNA Synthesis
-DNA replicates
-doubles the number of genes in the nucleus
3. G2: gap 2 or premitosis
-organelles within the cell replicate
-and other materials needed for cell division are produced, like RNA, proteins, etc.
-the M phase:
-the cell divides
-2 stages:
-mitosis: nuclear division
-4 major stages: prophase, metaphase, anaphase, telophase
-cytokinesis: cytoplasmic division
-the G0 phase: nondividing cells
-it’s stopping point within G1
-these cells exist, but are stuck here  don’t pass through the rest of the cycle and don’t divide
-skin cells constantly replace themselves, so they are NOT here
-brain and nerve cells don’t replace themselves, so they ARE here
-this is why brain and spinal cord damage can’t be repaired
-liver cells: stays in cell cycle until liver reaches its size  then its cells go into G0
If liver is injured: cells hop back in cycle until the liver once again reaches its size
-most cells in adult multicellular organisms are in G0
-these cells are metabolically active and specialized to perform the tasks necessary to sustain the
life of the organism
DNA Structure
-DNA molecules consist of two strands called a double helix
-in 1953, James Watson and Francis Crick proposed this structure
-the backbone, or sides of the DNA molecules are made of sugars and phosphates
-the “rungs” of the DNA molecule are made of 2 nitrogenous bases
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-base pairing depends on how many hydrogen bonds each nitrogen base can form with its counterpart
-cytosine only pairs with guanine and thymine only pairs with adenine
-cytosine only pairs with guanine because 3 hydrogen bonds hold them together, and adenine
only pairs with thymine because two hydrogen bonds hold them together
-purines are paired with pyrimidines
A– – – – – – – T
G – – – – – – –C
-the sugar-phosphate backbones are facing opposite directions
-because the strands are parallel but run in opposite directions, the structure is called antiparallel
-covalent bonds—between sugars and phosphates and between sugars and bases
-hydrogen bonds—between base pairs
-while DNA is a double strand, RNA is a single strand
-DNA forms the chromosomes, units of genetic information, that pass from parent to offspring
-DNA structure:
sugars (deoxyribose)
phosphate group
Nitrogenous bases
adenine = thymine
30%
30%
guanine = cytosine
20%
20%
Erwin Chargaff’s rules:
-each complement base is
equal in amount
-all four together make 100%
Nucleic Acids
-nucleic acids store and transmit genetic information
-the instructions in DNA are “copied” to RNA, ribonucleic acid, which directs the synthesis of proteins
-a nucleic acid is a polymer of nucleotides
-a nucleotide is composed of three parts:
1. 5 carbon sugar (pentose)
-either ribose or deoxyribose
2. a nitrogenous base
-there are 4: adenine, thymine, cytosine, guanine
-bases are either single or double rings of carbon, hydrogen, and nitrogen
3. a phosphate group
-has a negative charge
-the sequence of nucleotides in DNA ultimately determines the sequence of amino acids in protein
DNA Synthesis
-occurs during the S phase of the cell cycle
-this is a critical step in the cell cycle because it replicates the DNA, so one of each identical
chromosomes can go to the new cells
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-the structure of DNA is important in understanding how DNA replicates
-the overall structure of the molecule is a double helix
-the backbone of the molecule consists of alternating sugars and phosphates held together by
covalent bonds
-the rungs of the DNA molecules are composed of nitrogen pairs
-a purine (adenine or guanine) is always bonded to a pyrimidine (thymine or cytosine)
-if u look at the alternating sugar and phosphate bonds on one side of the DNA ladder and compare
them to the opposite side you will see: they are facing in opposite directions—one faces up, the other
faces down
-this structure is referred to as antiparallel and is important in determining the direction in which
the new strands of DNA are synthesized
-the process can be divided into 3 major parts:
1. binding of enzymes to existing DNA
2. unwinding of the double helix
3. synthesis of new matching strand for each existing strand
-these enzymes and proteins are:
-helicase- unwinds double helix
-topoisomerase- prevents tangling of helix
-single strand binding proteins- prevent strands from rejoining
-DNA polymerase
-breaks hydrogen bonds between nitrogenous bases
-brings in new DNA nucleotides
-works 5’ to 3’
-RNA primase:
-puts in 3-5 RNA nucleotides to which the DNA nucleotides can attach
-DNA polymerase-replaces RNA nucleotides
-“proofreads” for errors
*DNA polymerase can’t add or join new DNA nucleotides to something that’s not there  so RNA
primase is used to put in RNA nucleotides that the DNA nucleotides can attach to
-think of it like painting a black table yellow:
-you can’t just paint the table yellow (yellow paint = DNA nucleotides from DNA polymerase)
-you need a white coat called primer (primer = RNA nucleotides from RNA primase)
-the primer isn’t the final color, the yellow replaces the primer (RNA nucleotides get replaced
by DNA nucleotides)
-a replisome consists of all of the enzymes listed above as well as the strand of DNA being copied
-replisomes move in both directions
-when the DNA molecule “unzips”, it separates into two strands when the hydrogen bonds between
base pairs are broken
-this “unzipping” process occurs in many locations throughout the length of the chromosome
-these specific sites are called replication origins
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-multicellular organisms: have many replication origins and replisomes
-bacteria: have one replication origin and replisome
-DNA “unzips” at many places and has many replication origins
-more efficient  replication is faster
-the “unzipping” results in exposed bases on each side of the DNA ladder
-you might expect that new DNA nucleotides would come in to base pair with the exposed bases
-however, the enzyme DNA polymerase can only add new nucleotides to a pre-existing strand of
DNA
-so instead, the enzyme RNA primase first adds a short strand of RNA nucleotides, called a RNA primer,
to being the replication process
-the RNA nucleotides will later be replaced with DNA nucleotides
-once a few nucleotides of FNA primer are in place, the enzyme DNA polymerase begins adding new
DNA nucleotides
-remember: a nucleotide consists of sugar (deoxyribose), a phosphate group, and a nitrogenous
base (A, T, G, or C)
-the nitrogenous base sequence of the existing DNA strand determines the base sequence of the
matching strand
-ex: wherever thymine is on the original strand, adenine is added to the new strand
-the synthesis of the two new sides of the DNA molecule occurs in opposite directions
-always from 5’ to 3’
-one new strand is synthesized continuously into the replication fork  this is the continuous or leading
strand
-the other new strand is synthesized in short segments out of the replication fork  this is the
discontinuous or lagging strand
-these short pieces are called Okasaki fragments and are eventually joined together by an enzyme called
DNA ligase
-the overall process results in two identical copies of the DNA molecule
-this process is called semiconservative replication —each DNA molecule consists of half “old” and half
“new” DNA
-after replication, the DNA strands, called daughter strands, will be more compactly stored in the cell
-to do this, the DNA is wrapped around proteins called histones which are further bundled together to
form nucleosomes
-nucleosomes- a group of usually 8-10 histones
-allows DNA to take up a lot less space
-this coiling results in the highly coiled chromosome structures that are visible during mitosis in the cell
cycle
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DNA replication:
-the DNA molecule unzips
-DNA polymerase adds DNA nucleotides from 5’ to 3’
-DNA polymerase adds new DNA nucleotides
continuously INTO the replication fork on the leading
strand
-DNA polymerase adds new DNA nucleotides OUT of
the replication fork on the lagging strand
-the lagging strand is added in pieces called Okazaki
fragments
-DNA ligase is an enzyme that connects the fragments
of the lagging strand
-the parental strands are the template or mold
-DNA unzips at many replication origins-more efficient: replication is faster
-the replication bubbles expand
-the red = the new strands being added by DNA
polymerase
-the blue = the parental strands
ECT
-Semiconservative replication:
A ---T
G ---C
T ---A
C ---G
parental strand
A
G
T
C
T
C
A
G
the enzyme
helicase unzips the
DNA molecule
A
G
T
C
T
C
A
G
A
G
T
C
T
C
A
G
-DNA polymerase adds new
DNA nucleotides
-two identical strands of DNA:
daughter strands
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DNA Repair
-a mutation occurs when there is any change in the sequence of a cell’s DNA
-mutations may be nonharmful or silent, harmful, or sometimes lethal
-the new DNA strands must be exact complements of the parental strands
-the likelihood of mistakes occurring is reduced because the enzyme DNA polymerase proofreads and
corrects any errors that occur during replication
-the process called excision repair is when the mutations are repaired
-when mistakes are detected, the mistakes are “cut out” and replaced with the correct
nucleotides
-mutagens are chemicals that are environmental factors that cause mutations
-while mistakes can still occur, the proofreading activity by DNA polymerase reduces the number of
mistakes from 1 in 10 thousand base pairs to only 1 in 10 million base pairs
-most mutations are known as mismatches because they consist of base pairs that cannot form
hydrogen bonds (like adenine and cytosine- they can’t pair up no matter what)
-mutations that persist to the next cell division are inherited by the daughter cells
-many scientists believe that the accumulation of many of these mutations over a lifetime may result in
different types of cancer
Mitosis and Cell Division
The Stages of Cell Division
-it’s important that the process of cell division occur correctly because this process produces 2 new cells
and if it doesn’t, then the cells can be produced incorrectly with mistakes and they won’t survive
chromosomes
-chromosomes are units of genetic information
-they are made of DNA molecules
-chromosomes are found in the nucleus
-when do you call chromosomes what???:
-chromatin: when chromosomes are all tangled together
-during interphase and telophase and cytokinesis
-sister chromatids: when chromosomes are replicated and attached together by a centromere
-during prophase and metaphase
-chromosome: when chromosomes are long and individual
-during anaphase
-there are 46 chromosomes in our cells
-chromosomes are composed of chromatin
-in the early stages of mitosis, the chromatin is condensed and becomes visible, and untangles and coils
back on itself
-chromatin: mostly made of DNA and also protein (histones)
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-the DNA is able to fit into the nucleus of the cell:
-the DNA is packaged  the DNA molecules are wrapped around histone proteins which are
grouped together, in groups of 8-10 histones, called nucleosomes
-the centromere joins together the sister chromatids
-it’s found at the center of the chromosomes
-separation of the chromatids is called chromosome segration
-if segregation occurs correctly, each new nucleus receives one copy of each chromosome
-a mistake at this stage would be one nucleus with two chromosomes and the other nucleus with
none  daughter cells with this mistake are celled aneuploid cells
Interphase
(G1—S—G2)
-chromosomes appear in the form of chromatin— appears as a dark granular mass, so you can’t really
see the chromosomes
-chromatin: mostly DNA and proteins (histones)
-chromosomes have replicated during the S phase
-the 3 events:
-G1-prereplication
-S-DNA synthesis
-G2- premitosis
the M phase
-mitosis (nuclear division)
-cytokinesis (cell division)
4 stages of mitosis
-the result of mitosis is the production of two nuclei each with a duplicate set of chromosomes
-scientists still don’t completely understand how chromosomes move during mitosis
1. prophase
-the longest phase of mitosis
-begins when the nuclear membrane breaks down into small vesicles
-early prophase:
-the chromatids become visible because the chromatin has condensed and thickened
-the chromosomes appear as two identical sister chromatids
-sister chromatids are attached at the centromere
-contents of the nucleolus and nuclear membrane disperse and they appear to disappear
-centrioles, which are normally found outside the nucleus, separate and move to opposite sides
of the nucleus
-the centrioles contain tubulin, a microtubule protein
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-late prophase:
-the spindle, a network of proteins that helps to move the chromosomes apart, is produced from
the centrioles
-spindle fibers begin to attach to the sister chromatids at their kinetochores
-near the end of prophase, the coiling of the chromatids becomes tighter
-sister chromatids appear short and thick  coiled back on themselves so it’s easier to move around
*even though plants don’t have centrioles, they still produce spindle fibers which help to pull
the chromosomes apart
2. metaphase
-the shortest phase of mitosis
-sister chromatids align at the equator or metaphase plate
-spindle fibers attach to the kinetochores of each chromatid
-the spindle, which are arranged in the starlike pattern around the poles of the spindle, are often
called asters which is the greek word for star
3. anaphase
-sister chromatids separate as spindle fibers shorten
-begins when centromeres that join the sister chromatids spit
-this causes the chromatids to split and form separate chromosomes
-the chromosomes continue to move until they have separated into two groups
-each group is now found near the poles of each of the spindles
-ends when the chromosomes have stopped moving
4. telophase
- chromosomes uncoil to form a tangle of chromatin
-this occurs in two regions—where the nuclei of the daughter cells will form
-the nuclear envelope reforms around the chromatin
-the spindle breaks apart and the nuclear envelope and nucleolus once again become visible
-this marks the end of mitosis
Cytokinesis
-often occurs during telophase
- the cytoplasm of the cell divides
-this results in the production of two complete and individual daughter cells
-cytokinesis is different in plant and animal cells:
-plants:
-cell plate forms from the center of the cell outward
-plants don’t have centrioles
-animals:
-cleavage furrar: how and where the cytoplasm divides
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Control of the Cell Cycle
-scientists wondered:
-why don’t cells keep duplicating their chromosomes until the sister chromatids have segregated?
-what prevents mitosis from starting before the cell has completed the S phase?
-if the stages were not in the right order or time, it would be disastrous
-huge numbers or copies of their chromosomes
-cells would start separating while DNA was still replicating
-scientists found that S-phase cells cause G1 nuclei to move into the S phase and that M-phase cause G2
nuclei to move into mitosis
-there are factors in S-phase cells that enter G1 nuclei and start replication, but don’t enter G2 cells
-same with M-phase cells: they can move G2 nuclei into mitosis, but not G1
-research from very diverse organisms all revealed a same basic mechanism for cell cycle control that
humans use
cyclins
-proteins that regulate progression through the cell cycle
-when cells leave G0 and commit to a round of the cell cycle, these proteins start to accumulate and
quickly disappear as the cycle goes on
-the most important cyclins = G1 and mitotic
- G1 cyclins accumulate in late G1 and reach a peak during S phase and disappear
-mitotic accumulate after DNA systhesis is complete and peak during metaphase and disappear
-cyclins activate kinases (enzymes that activate other enzymes needed for progress through the cell
cycle)
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Chapter 9
3 types of RNA
-in addition to these three types of RNA eukaryotic cells have a variety of small nuclear RNA molecules
that interact with specific proteins during RNA processing
-some RNA molecules act as catalysts, like enzymes
-many viruses store genetic information as RNA
mRNA or messenger RNA
-carries copies of the instructions for assembling amino acids from DNA to the rest of the cell
-temporary copy of a gene that encodes a protein
-transcription is the process that makes mRNA
-provides the pattern that determines the sequence of amino acids that are added to the polypeptide
chain in a process known as translation
rRNA or ribosomal RNA
-combine with proteins to make up ribosomes
-80% of the RNA in a cell is rRNA
tRNA or transfer RNA
-transfers each amino acid to the ribosome to help assemble proteins
-each amino acid that will be used in making the protein is attached to this
Importance of Proteins
-proteins play a very important part in the function of any living system
-they have 8 functions:
-make up structural features
-are enzymes, which catalyze and regulate chemical reactions
-provides ATP
-carry oxygen to the blood (hemoglobins)
-carry chemical messages as hormones like insulin help maintain homeostasis
-cell signaling also involves protein receptor molecules attached to the cell membrane that pass
along signals to a series of regulatory enzymes inside the cell
-a protein’s structure determines its function, and information expressed from the code in DNA
determines the structure of proteins
-many enzymes have cavities or pockets that bind only specific substrate molecules
-ex: the enzyme lysozyme, found in egg white and tears, helps destroy harmful bacteria by cutting a
polysaccharide found in bacterial cell walls
Protein Synthesis
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Transcription
How DNA is converted to RNA
gene
A ---T
G ---C
T ---A
C ---G
goes back
to DNA
A
G
T
C
U
C
A
G
T
C
A
G
nucleus
mRNA leaves through
nuclear pores
-takes place in three stages:
1. initiation
-when the enzyme RNA polymerase attaches to a specific region of DNA
-this attachment site is called the promoter region because it promotes transcription and is
located just before the segment of the DNA coding strand that will be transcribed
2. elongation
-RNA polymerase partially unwinds the DNA, exposing the coding strand of the gene
-it moves along the DNA away from the promoter site as it builds an RNA molecule
-the sequence of DNA nucleotides determines the sequence of RNA chain
-a single complementary strand of RNA, called a primary transcript, is made
3. termination
-when RNA polymerase reaches the terminator region, or the end of the DNA to be transcribed,
the enzyme and primary transcript are released from the DNA
-DNA never leaves the nucleus, so it’s converted into mRNA which can leave the nucleus
-RNA is like a disposable copy of a DNA segment
-RNA polymerase
-unwinds the DNA double helix
-breaks hydrogen bonds between nitrogen bases in DNA
-adds new RNA nucleotides
*it knows exactly where to bind in the chromosome
-binds only to DNA promoters, which have specific base sequences
-promoters are signals in RNA that indicate to DNA polymerase when to begin translation
-only a section of the chromosome is copied—this section is called a gene
-gene: small section of the chromosome that has genetic information
-only one strand of the DNA directs the synthesis of RNA
-this strand of DNA is called the template, sense strand, or master strand
-prokaryotes have one type of RNA polymerase
-eukaryotes have 3 RNA polymerases in the nuclei and each is responsible for making the 3 types of RNA
-the nucleolus is the site of RNA synthesis
-the nucleolus is also where rRNA and 70 other proteins are made into ribosomes
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mRNA processing
-takes place in the nucleus
1. MG (methyl guanine) cap is added to the “beginning” of the strand
2. poly A tail (10-25 adenines) is attached to the “end”
-the longer the poly-A tail, the longer the life span of a particular mRNA
-also helps transport mRNA out of the nucleus and helps the mRNA attach to a ribosome and begin
translation
*”beginning” vs. “end”
-provides protection against enzymes that break down nucleic acids
3. “splicing”
-introns are removed
(intervening)
-exons are joined
(expressed)
-protein enzymes catalyze the splicing of tRNA
-there is no correct sequence: it can be put together in many ways
-ex: antibodies are proteins made by the body to protect against antigens like viruses, bacteria,
dander, pollen, etc.
-different bodies make different antibodies  different antibodies due to being differently
spliced
-why?
-only certain information is needed for specific jobs to create different sequences
-there is more information than needed
-processing mRNA before it’s translated makes translation faster and more efficient because
there are less codons to be changed into amino acids
-a primary RNA transcript may contain as many as 200,000 nucleotides (the average for human cells is
5,000)
-mRNA in the cytoplasm averages only 1,000 nucleotides
-enzymes add additional nucleotides and chemically modify or remove others
-if introns are left in RNA, the consequences can be serious
-in addition to splicing, an important step in the processing of tRNA is the chemical modification of
several nucleotides and folding into a cloverleaf shape
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Translation
-steps of translation: initiation, elongation, termination
mRNA binds to the small ribosomal subunit (at the 5’ end)
the smallest ribosomal unit attaches to mRNA at the “start codon” AUG at the P site
the large ribosomal subunit attaches
a charged tRNA brings in an amino acid to the A site
the amino acid released from the tRNA is the P site is transferred to the amino acid (still
elongation
attached) to the tRNA in the A site.
*covalent bond called a peptide bond forms between amino acids
6. The uncharged tRNA in the P site moves to the E site
7. The ribosome shifts down to another mRNA codon
8. tRNA in the A site moves to the P site
9. the site is now open for the next tRNA with an amino acid
10. when the “stop codon” reaches the A site, a special protein (a release factor) binds to the codon
termination
in the A site to stop translation
11. the tRNA releases the polypeptide. The ribosome releases mRNA and tRNA and the ribosome
separates
12. the polypeptide chain moves to the ER (endoplasmic reticulum)
a) folded
b) sugars are added as markers
13. proteins are packaged an shipped in vesicles from the golgi apparatus for use outside the cell
-translocation: when the polypeptide chain moves from the P site to the A site
-the ribosome has 3 parts during this process: the small subunit, the large subunit, and the mRNA strand
-3 stages: initiation, elongation (adding more amino acids), termination
-hydrogen bonds are between tRNA and amino acids  are easily broken
-the mRNA strand is broken down afterwards and recycles
-the start codon is an amino acid (it’s methionine), but the stop codon is NOT an amino acid
-the longer the polypeptide chain, the longer the mRNA stays in the cytoplasm before it’s broken down
initiation
1.
2.
3.
4.
5.
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Mutations
-mutations:
-there are 2 type of mutations:
1. chromosome mutations
-when an individual inherits more or less than the normal number of chromosomes
-due to a problem during mitosis or meiosis
-are lethal to the cell most of the time
-ex: down syndrome
-when there is 3 pairs of chromosome 21
-causes similar facial features  not defined, babylike
-serious mental handicaps
2. gene mutations
-results in abnormal protein products
-gene disorders such as sickle cell, cystic fibrosis, and hemophilia are all due to gene mutations
-are due to a change in the cell’s DNA  mRNA  amino acids  polypeptide (protein)
-aren’t as harmful as chromosome mutations
-2 types of gene mutations:
-substitution
-one nucleotide with a nitrogenous base is substituted for another
-ATT GCC may be altered to ATC GCG (in DNA)
-wobble effect: a substitution will often not change an amino acid if the change is in the third
position or base
-deletions and insertions
-cause more serious mutations
-deletion: when at least one nucleotide is left out
-insertion: when a nucleotide is added
-the later the mutation, the less it affects the strand
-both mutations cause a “frame shift”
- a frame shift
-if mRNA is AUG (met) CCC (pro) GCA (ala)
-an insertion might be: AUG (met) ACC (thr) CGC (arg) A
missense: nucleotides
-a deletion might be: AUC (iso) CCG (pro) CA
not in triplets
-both result in the mRNA “read” as a different codon
-the result is a change in amino acids
Do mutations always change the protein?
-mutations in the 3rd base of a codon may not change the amino acid (wobble effect)
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-insertions or deletions that occur early in the mRNA change many amino acids
-insertions or deletions that occur late in the mRNA change fewer amino acids
-mutations that occur in introns (and are cut out) won’t affect the protein produced
Translation Errors
-most errors during translation are caught and corrected
-the most common translation error results from misreading the nucleotide sequence
-initiation determines exactly where translation will begin
-starting from this point, the grouping of bases into codons is called the reading frame
-if the start is shifted by one or two nucleotides in either direction, the frame changes
-a different sequence of codons and amino acids will result
-some errors are due to splicing mistakes or changes in DNA
-if a nucleotide changes so that a codon becomes a stop codon, translation can terminate partway
through the message  the result is a partial polypeptide
Viruses
-viruses: tiny particles that have no cells, yet they replicate and evolve
-called “particles” because they are not living
-Dmitri Ivanovsky: Russian botanist who discovered viruses
-found that the infective agent of tobacco mosaic disease passed through a filter that would have
retained bacteria  the virus was tobacco mosaic virus, TMV
-because they can’t do these things without help, viruses depend on the gene-expression machinery of
the host cells they infect
-Why are viruses not considered living?
-can’t reproduce on their own
-no normal cell structure: no organelles
-no metabolism
- no mitochondria or chloroplasts  no ATP
- are much smaller and simpler than cells
- don’t respond to stimuli, as cells do
-structure of viruses:
-contain a small amount of genetic material: DNA or RNA
-surrounded by a protein coat called a capside
-some contain a few enzyme molecules, like those needed for transcription of their genes
-some viruses that infect animal cells have a membrane envelope
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-viruses tend to be very specific
-if you have a virus or a cold, your cat or dog could not get it
-rhinovirus: a virus in the nose or nasal passages
-only in the nose, can’t infect the liver
-HIV infects T cells
-viruses trick cells
-cells are very good at recognizing foreign material, so viruses disguise themselves and attach to cells
-the virus then uses all of the cell’s structures: its ribosomes, its enzymes, etc.
-it turns the cell from a protein factory to a genetic material and protein (for viruses) factory
-the virus parts then assemble inside the cell and the cell explodes, or lyses
-2 types of viruses:
-bacteriophage
-infects the cells of bacteria
-ex: T2 is a bacteriophage that is a DNA virus-contains DNA surrounded by a protein
-the elongated structure attaches to bacterial cells and injects DNA
-retrovirus
-only virus particles with RNA
-goes from RNA which is read to DNA
-when retroviruses infect a cell, they produce a DNA copy of their RNA  this DNA is inserted
into the DNA of the host cell
-an enzyme called reverse transcriptase does the copying of RNA to DNA
-ex: HIV, which infects human cells, is surrounded by a protein and lipid membrane envelope
-the genetic material is RNA
-HIV also carries two molecules of the enzyme reverse transcriptase, ready to copy the RNA
after entry into a host cells
Lytic vs. Lysogenic Cycles of Viruses
-lytic infections
-the host cell’s enzymes replicate the viral DNA
-viral genes are transcribed and translated on the host’s ribosomes to make proteins for the out
capsule
-new viral particles assemble
-when there are many new viruses, the cell lyses (breaks open) and releases them to infect
other cells
-lysogenic infections
-the viral DNA (or a DNA copy of it) inserts into the cellular DNA
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-it is copied as the cell replicates
-there is little or no production of new viruses
-instead the genetic information for the virus is passes along to new cells
-sometimes an external stress, like starvation, of the host cell activates a lytic cycle of replication
-in animal cells, a few viral particles may be given off from time to time without lysing the cell
-when the viral particle emerges, it can pick up part of the cell membrane
-the membrane makes it difficult for the host to recognize the viral particle as an invader
-in tumor viruses, the cell may lose control of normal growth and become cancerous
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Infectious disease/The Hot Zone
Bacterial Infections vs. Viral infections
bacterial infections
-caused by pathogenic bacteria
-pathogenic bacteria are the small percentage of harmful bacteria, although most bacteria are harmless
and usually beneficial
-bacteria reproduce asexually through binary fission
viral infections
-viruses replicate through either lytic or lysogenic cycles
How viral infections are prevented: vaccines
-vaccines: preparations of weakened or killed pathogens
-doctors give a sample of protein coat or virus that has the potential to make you sick but actually helps
you build immunity to the virus
-stimulates B and T cells as memory cells: they remember the virus and are ready to recognize and
fight the virus if it ever comes
How bacterial infections are prevented/ treated: antibiotics
-antibiotics are effective against bacterial infections because they interfere with aspects of bacterial
metabolism that are different from their hosts’ metabolism
-they are useless again viruses because viruses do not have their own metabolism
Practices to reduce infections (aseptic tenchinque)
-aseptic technique: not letting object, like an agar plate with E.coli, come in contact or contaminated
with any other bacteria from the air or anywhere else
-it involves using the clamshell to open the agar plate and bleaching the plates when you are finished
and need to dispose of them
20
Chapter 12: Reproduction
Asexual Reproduction
-requires one single parent
-is when this one parent cell splits into 2 exact copies
-survive better in a stable environment that doesn’t change
-a group of genetically identical cells or organisms produced through asexual reproduction is called a
clone
-cloning is taking a living thing and making an exact copy of it
-types of asexual reproduction
-prokaryotes reproduce by simply dividing in two, called binary fission
-budding is when a new organism grows off an existing organism
-ex: hydra
-fragmentation is when an organism breaks into pieces and the small fragments of the organism spread
over great distances in the wind or in the fur of an animal and produce new organisms
-ex: planaria
-vegetative reproduction is using any structure that’s not structure to grow a new plant
-is efficient in filling an area with plants, but it is less successful in quickly spreading plants to new
locations
-ex: potatoes- new potatoes can grow from each eye
-doesn’t produce variety: the traits of new organisms are exactly the same as the traits of the “parent”
-disadvantage: all the organisms would die if there is a sudden change in the environment because
they would have the same traits that wouldn’t help them survive
-ways to provide variation for asexual reproduction:
1. conjugation
2. mutations
Sexual Reproduction
-when two different parent cells come together to produce one cell
-each parent cell gives half of their DNA
-most organisms are produced this way
-beneficial: provides variation!!
-important because it helps a species survive
-it allows at least some of the species to survive if the environment changes
-variation: differences of individuals of the same species
-traits that are beneficial to a species pass to offspring through fertilization
-over time, it is possible for characteristics of a population to change over time: this process is called
evolution
21
Sexual Reproduction in Microorganisms
-prokaryotes reproduce asexually through binary fission
-they do however, exchange genetic information
-a tube of cytoplasm can temporarily connect some bacterial cells and some DNA passes through this
tube: this process is called conjugation
-like sexual reproduction, it promotes genetic variation but it doesn’t produce offspring
-conjugation often occurs in many unicellular eukaryotes
-microorganisms that reproduce both asexually and sexually include many unicellular or colonial green
algae
-the life cycles of these organisms include both haploid and diploid stages, a pattern called alternation
of generations
-these organisms are haploid during most of their lives. sometimes they produce gametes, which fuse
into a diploid zygote. eventually, meiosis produces more haploid cells
-alternation of generations is common in parasitic microorganisms like plasmodium
-many fungi and other microorganisms switch from asexual to sexual reproduction in response to
changes in their environment
-stresses like poor nutrition induce sexual reproduction in many such organisms like mushrooms
Chromosome Numbers
-each species has a specific number of chromosomes
-prokaryotes have only one major chromosome, consisting of a single circle of DNA. one or more
plasmids carry only a few genes, such as those responsible for resistance to antibiotics
-the number of chromosomes varies in eukaryotes, but they all have an even number because an
individual gets a set of haploid chromosomes from each parent which makes a diploid set of
chromosomes for the individual
-cells of most organisms that reproduce sexually have pairs of similar chromosomes called homologous
pairs
-each parent provides one member of each homologous pair
-22 homologous pairs are autosomes and there is 1 pair of sex chromosomes
-diploid: the total number of chromosomes
-the symbol for it is 2n
-haploid: half of the diploid number of chromosomes
-the symbol for it is n
-cells that carry a double set of chromosomes are called diploid
-cells with just one set of chromosomes are called haploid
-autosomes: the other 44 chromosomes in the body
-sex chromosomes: 2 out of 46 for humans
-homologous pairs are similar in structure
-an exception is the pair called sex chromosomes which are called nonhomologous in males
-homologous pairs carry the same genes, though their DNA sequences may be slightly different
22
-in asexual reproduction, the cells of parent and offspring carry identical sets of chromosomes
-in sexual reproduction, two parents contribute chromosomes to offspring
-for this reason, the gametes that fuse during sexual reproduction are haploid and carry half the normal
number of chromosomes
-if gametes were diploid, the number of chromosomes would double in each generation
-somatic cells: normal body cells, or any cell that isn’t a reproductive cell (an egg or sperm cell)
-gametes: reproductive cells (sex cells or germ cells)
-in sexual reproduction, each parent produces haploid gametes
-male gametes are sperm and female gametes are eggs or ova (singular: ovum)
-fertilization: process where two complementary games come together and their nuclei fuse
-zygote: the one diploid cell produced by fertilization
-in sexual reproduction, meiosis and fertilization are complementary processes
-meiosis produces haploid gametes, while fertilization restores the diploid chromosome number
-mitosis: nuclear division where the chromosome number stays exactly the same: diploid number is
maintained
- meiosis: nuclear division where the chromosome number is reduced to half: diploid  haploid
-in fungi and simple plants, meiosis produces different types of haploid cells called spores
-most spores can develop into haploid organisms without fertilization
Meiosis
Meiosis vs. Mitosis
-mitosis:
-occurs in eukaryotes
-occurs in phases
-nuclear division
-number of chromosomes in the daughter cells is the same as the parent cells: diploid number is
maintained
-the daughter cells are genetically identical to each other and the parents
-2 daughter cells are produced
-meiosis: converts diploid somatic cells to haploid gametes
-occurs in eukaryotes
-occurs in phases
-nuclear division
-the number of chromosomes in the daughter cells is half of the parent cells
-the daughter cells aren’t genetically identical to each other and the parents
-4 daughter cells are produced
-only involved in sexual reproduction
23
-cells divide twice during meiosis, but the chromosomes aren’t duplicated after the first division: this
halves the chromosome number from 2n to n
-meiosis distributes a random mixture of maternal and paternal chromosomes to each gamete which
results in new genetic combinations
-genes are sections of chromosomes that contain specific genetic information and are located in
chromosomes
-meiosis occurs in testes for males and ovaries for females
-homologous pairs pair up side by side during prophase I and exchange corresponding genes in a process
called crossing over: it changes each chromosome into a mixture of maternal and paternal genes,
adding to the genetic variety of gametes and allows the next generation to get different traits
Crossing-over
paternal
maternal
homologous pair homologous pair
paternal
maternal
homologous pair homologous pair
The Phases of Meiosis
Interphase
-homologous pairs are present
-during the “S” phase, chromosomes replicate (this is the only time!)
Meiosis I
1. prophase I
-tetrads are formed—tetrads are sister chromatids that are homologous
-crossing over may occur
-the nuclear membrane disappears and centrioles separate
-spindle fibers form
-chromosomes shorten and thicken for the 1st time
2. metaphase I
-homologous pairs align at the equator
3. anaphase I
-homologous pairs separate
-independent assortment of chromosomes occurs
4. telophase I/cytokinesis
-the first stage in which the cells are haploid
-two haploid cells are formed
-chromosomes lengthen again and the nuclear membrane reforms
24
Meiosis II
1. prophase II
-sister chromatids shorten and thicken for the 2nd time
2. metaphase II
-sister chromatids align at the equator
3. anaphase II
-sister chromatids separate
-sister chromatids move to the poles
4. telophase II/cytokinesis
-four haploid cells are formed
-the nuclear membrane reforms
Sexual Reproduction in Plants
(sorry no pictures of mosses or flowers this time…it would take wayyy to long…so just use your lab for that part.)
-plants generally reproduce sexually
-however, many plants can also reproduce asexually and some have lost the ability to reproduce
sexually
Mosses
-simple plants, like mosses, spend most of their lives in the haploid stage
-these plants require a moist environment to reproduce
-their sperm swim through wet soil to reach the plant’s female reproductive structures
-spores fall to the ground and grow into tiny haploid plants that produce male and female gametes
-after fertilization, the zygote grows into a new diploid fern
-mosses are bryophytes which never get taller
-they get water through osmosis because they don’t have a transport system like xylem or phloem
tubes
-the sporophyte grows out of the gametophyte
-the sporophyte is temporary and has the capsule at the top of it which opens and releases spores
-the gametophyte produces gametes (egg and sperm cells)
Complex Plants
-more complex plants, like flowers, are large diploid structures
-their haploid stage is just a small tissue in their reproductive organs – the ova are protected inside
-unlike fern sperm, the sperm of seed plant’s don’t need to swim through wet soil
-wind of symbiotic animals like bees, bass, and butterflies carry the sperm that has been packages inside
tough protective pollen grains to the female organs
25
Self-fertilization in Pea Plants
-the petals of the pea flower completely enclose the reproductive organs
-as a result, the pollen from the anthers falls on the stigma of the same flower
-pollen tubes grow down through the female reproductive organ to the ovules in the ovary
-the ovules develop into seeds, and the ovary wall develops into the pea pod
-if you plant a bean or pea seed and water them, they will produce
Flowers
-the most successful plants are the flowering plants
-haploid cells in the flowers form gametes
-each flower may produce sperm, ova, or both
-at the center of an ovum-producing flower, one or more modified leaves called carpels fuse edge to
edge, forming a hollow structure
-the base of this carpel is the ovary which contains one or more small structures called ovules
-the ova develop in the ovules
-within each ovule, a specialized cell undergoes meiosis—4 haploid cells result, three of which
disintegrate; the fourth cells divides by mitosis to produce 7 cells—one of these cells becomes the
ovum
-cells in the anther undergo meiosis, producing four haploid cells
-each haploid cell divides mitotically to produce a pollen grain containing two cells—a tube cell and
a second cell that divides to produce two haploid sperm nuclei
-sexual reproduction begins as the anthers shed pollen
-in nonflowering plants like pine trees, wind carries the pollen to the carpel of the same or other flowers
-insects, bats, and other animals that eat flower parts carry the pollen of flowering plants
-pollination: the transfer of pollen from anther to carpel
-cross pollination: pollination between two different plants of the same species
-it increases genetic variation by combining chromosomes from two parents
-many intricate mechanisms for pollination have evolved
-some insects and flowering plants have became so completely dependent of each other that
neither can reproduce without the other
The Fertilization Process
-when pollen lands on the tip of the carpel tunnel, or the stigma, the pollen grain germinates and forms
a pollen tube that grows toward the ovule, carrying the sperm nuclei
-fertilization occurs when one sperm nucleus fuses with the egg
-the resulting diploid zygote divides mitotically and eventually develops into an embryo
-the second sperm nucleus fuses with the two polar nuclei, forming a triploid cell that develops into the
endosperm
-fertilization ends the short haploid stage in the life cycle of a flowering plant
-the ovule then becomes the seed, forming a protective coat around the embryo and endosperm
26
-auzin produced by the seeds stimulates the ovary to enlarge and develop into a fruit
How seeds spread
-seeds spread in various ways
-many fruits are carried by the wind
-some are adapted to stick to animal fur
-many seeds remain inside fruits, which may be eaten by animals and transported great distances in
their digestive systems until they eventually deposit the undigested seeds along which other organic
wastes which actually help nourish the seeds in their new location
-flowering plants are found in widely different environments
Several adaptations contribute to this:
-the dominance of the diploid stage in the life cycle, which allows development of complex structures
-the evolution of pollen, which allows the transfer of sperm from plant to plant without the need for
water
-the evolution of the seed and endosperm, which protects the dormant embryo and provides food and
protection for the young plant
-a variety of adaptations that promote pollen and seed dispersal
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Chapter 13: Patterns of Inheritance
Mendelian Genetics
-Gregor Mendel was a monk, gardener, high school science teacher, mathematician, and scientist
-he is called the “father of genetics”
Mendel’s Experiment
-he used garden peas to study heredity
-peas are very easy to grow and he could study many generations during his 8 years of experimenting
and are also self-fertilizing
-mendel decided to study traits that didn’t fit the blending theory
-seed shape
-embryo color
-flower and seed coat color
-pod shape
-pod color
-flower position
-stem length
-mendel worked with his plants for several years to be sure he had true-breeding varieties for each of
the traits he selected
-true-breeding plants produce offspring identical to themselves generation after generation
-mendel then crossbred his plants and classified all the offspring
-he mated a plant with round seeds and a plant with wrinkled seeds
-he found that the next generation only produced round seeds
-when those plants self-fertilized, the next generation was wrinkled and round
-mendel demonstrated with these pea plants that both parents pass on to their offspring genetic factors
that remain separate generation after generation
Alleles
-the concept of alleles has replaced mendel’s genetic factors
-an allele is one of two or more possible forms of a gene
-each allele of a particular gene has a different base sequence
-for example: the allele for round seeds encodes an enzyme that produces round seeds, and the allele
for wrinkled seeds is a different form of the same gene
-a different allele can code for a different color
-one allele can code for a yellow pod and the other allele can code for a green pod
-all organisms have genes that exist as different alleles
-many traits like hair color, skin color, nose shape, and handedness result from the complex interaction
of several genes with each other and the environment
28
Genes and Chromosomes
-the arrangement of genes in chromosomes differs in eukaryotes and prokaryotes
-in eukaryotes:
-chromosomes are long molecules of DNA wrapped around protein
-but only part of this DNA codes for proteins
-the other part, noncoding DNA or introns, isn’t translated
-about 1.5% of their DNA is translated as proteins
-in prokaryotes:
-bacteria have a single circular chromosome with little associated protein
-their genes generally don’t have introns
-about 90% of their DNA is translated
-many bacteria also have plasmids- small circles of DNA that contain additional genes
-plasmids may move from one bacterium to another and can carry genes that provide resistance to
antibiotics
-homologous chromosomes carry the same genes, but their genes may be present as different alleles
-to distinguish homologous chromosomes from each other:
-staining: the stains bind to specific regions of the chromosomes, creating banding patterns specific
to each chromosome
-chromosome painting: fluorescent dyes of different colors are chemically bonded to short pieces of
DNA (probes) that bind to genes on different chromosomes – this process stains each homologous
pair a different color
-chromosomes are easiest to study in the condensed form they have during cell division
-for this reason, white blood cells are used most to study human chromosomes
-chemicals are added to stop cell division during metaphase and the cells are looked at under a
microscope
-this technique helped determine that human cells (except gametes) have 46 chromosomes
-stained chromosomes can be photographed under the microscope
-a karyotype is a display of individual chromosomes cut out of an enlarged photograph and arranged by
size and shape
-karyotypes of fetal cells can be used to check for suspected chromosomal abnormalities in developing
fetuses
Probability and Genetics
-diploid organisms usually carry different alleles of many genes
-the distribution of those alleles among games in meiosis and the combination of alleles that come
together in fertilization are a matter of chance
-probability predicts the chances that a certain event will occur
-can be expressed as a fraction or percent
-geneticists use probability to predict the alleles of the offspring of various crosses, or matings
29
-mathematical tests can help show whether the difference between the observed and expected results
is significant (in other words: if the difference is due to change or to some other factor)
-genetic counselors use probability to help parents assess the risk of passing on a genetic disorder to
their children
-expected genotypes are the genotype that has been predicted through probability calculations and are
arrived at mathematically
-observed genotypes are the genotypes of individuals from actual fertilization experiments and are due
to chance
-the larger the sample size, the wider range of results you have, and the outcome will be more correct
Inheritance of Alleles
-monohybrid cross: a genetic cross between individuals that only differ in one trait
-ex: mendel crossed plants that differed in only seed shape
-parental (P) generation: the parental organisms involved in the first genetic cross
-first filial or F1 generation: the first generation of hybrid offspring in a genetic cross
-ex: the plants that grew from the parental seeds produced all round seeds for the F1 generation
-second filial or F2 generation: offspring resulting from interbreeding of the hybrid F1 generation
-ex: mendel allowed the F1 generation plants to self-fertilize, and had a 3:1 ratio of round to
wrinkled seeds for the F2 generation
-for each of the seven traits mendel studied, only one trait of each pair was visible in the F1 generation
-dominant: an allele that masks the presence of a recessive allele of the same gene in a heterozygous
organism
-recessive: an allele that’s masked and not expressed in a heterozygous organism
-(still using the ex from above): the round seeds are dominant and wrinkled seeds are recessive
-the recessive trait reappeared unchanged in the F2 generation
-mendel used the ratio 3:1 to describe the ratio of traits, dominant to recessive
-he used mathematics to conclude that each true-breeding plant has two identical copies of the
factor for a particular trait
-the allele for a dominant trait is represent by a capital letter and the allele for a recessive trait is
represented by a lowercase letter
-most multicellular organisms are diploid, so they have two alleles for every gene
-genotype: genetic make up of an organism
-ex: purebred round seeded plant = RR; wrinkled seeded plant = rr
-homozygous: the genotype where both alleles are the same; having 2 identical alleles for a given trait
-ex: RR or rr
-heterozygous: the genotype where the 2 alleles are different; having 2 different alleles for a given trait
-ex: Rr
-the genotype of each individual is responsible for its phenotype
-phenotype: an individual’s appearance or observable characteristics
30
-because the round-seeded phenotype is dominant, both the homozygous RR and heterozygous Rr
will produce plants with round seeds
-a punnett square can be used to calculate ratios of genotypes and phenotypes
-to follow the inheritance of 2 traits at once, mendel made dihybrid crosses
-dihybrid cross: a genetic cross between individuals that differ in 2 traits
Mendel’s 3 Laws of Inheritance
1. law of segregation
Bb
B
or
b
-the alleles of each gene segregate during meiosis when homologous chromosomes are divided
among gametes
-when gametes formed during meiosis, only one copy of the factor went into each pollen or egg cell
-at fertilization, the F1 generation received a round seed factor from one parent and a wrinkled seed
factor from the other parent  only one of these factors, either round or wrinkled, went into each
gamete formed by the F1 plants
2. law of independent assortment
BB
Bb
Bb x Bb
Bb
bb
-alleles for one trait assort, or divide up, among the gametes during meiosis, independently of
alleles for other traits
3. law of dominance
-the presence of dominant traits masks recessive traits (except during incomplete and codominance)
Sex Determination
-chromosomes come in matching pairs except for the sex chromosomes, which may be different
-this pair of chromosomes determines the sex of the individual
-the sex chromosomes are labeled X and Y
-females: XX
-males: XY
-all the eggs produced during meiosis have an X chromosome, and half the sperm produced have an X
while the other half have a Y chromosome
*so the sperm determines the sex of the offspring (if the sperm has an X =female; if the sperm has a
Y=male)
-insects: females have 2 X chromosomes and males only have one X but no Y
-birds, some fish, and some insects have a Z-W system of sex determination
-males have 2 matching ZZ chromosomes and females have ZW
31
-some plants have separate female and male plants and have sex chromosomes that follow the X-Y
system of sex determination
-most plants and some animals have no sex chromosomes
Incomplete dominance
-occurs when the dominant trait isn’t fully expressed
-the heterozygote appears as a “dilute” form of the dominant trait
-ex: when red snapdragons are crossed with white-flowered snapdragons, all the F1 plants are pink
Codominance
-occurs when both dominant and recessive traits are equally expressed in the heterozygote
-when both phenotypes appear in heterozygous individuals
-ex: roan- when there’s both red and white in an individual although red is dominant and white is
recessive
Multigene traits
-blood types also involve multiple alleles
-there are 3 alleles for blood type, but no individual has more than 2 of the alleles
-blood types are important in transfusion
-if someone with type A blood receives a transfusion of type B blood the donated red cells clump
together, clogging the blood vessels
-this clumping is caused by antibodies, which are defensive proteins found in the blood
-antibodies bind to foreign substances and are an important defense against infection so the
person with type A blood produces anti-B antibodies
Sex-Linked or X-linked Traits
-sex linked traits: traits that are carried only on the X chromosome
-males have them more often than females
*they only have one X chromosome
-the Y chromosome does contain genes, but not sex-linked genes because they’re only carried on the X
-all X-linked alleles are expressed in males, even if they are recessive
-examples:
-red-green colorblindness (the inability to distinguish colors)
-cause: 3 human genes associated with color vision are located on X chromosomes in males—
defective version of any one of these genes cause colorblindness
-hemophilia (a disease where the blood doesn’t clot normally)
-sex influenced traits: traits whose presence is influenced by male hormones
-examples:
-bird feather coloration- male birds are brighter than females
-male pattern baldness
32
-ex: hemophilia
gene for blood clotting protein
female
H H
X X
XHXh
XhXh
male
normal
XHY
XhY
hemophilia
-it’s very rare for a girl to have hemophilia
-must have a mom that’s a carrier or has the disease and a father with the disease
-calico cats = always female!
female
B B
calico cats
XX
XbXb
XBXb
male
XBY
XbY
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Human Genetic Disorders
Characteristics of Genetic disorders
-turners syndrome
-aneuploid female, often short and sterile with webbing at the neck
-sickle cell anemia
-results in a defective hemoglobin protein
-heterozygotes are resistant to malaria
-common among Hispanics and Africans and their descendents
-Huntington’s disease
-symptoms do not develop until late in life (30-50)
-autosomal dominant inheritance
-offspring have a 50% chance of inheriting the disorder
-tay-sachs
-autosomal recessive disorder, results in fatty accumulations in the brain and early death
-heterozygotes tend to be resistant to tuberculosis
-common among Eastern Jews and their descendents
-hemophilia
-sex-linked disorder, formerly treated with blood transfusions
-a chromosome mutation that results in a failure to produce sufficient fibrin, important in blood
clotting
-sex-linked disoreder, effectively treated with recombinant DNA (rDNA)
-klinefelters syndrome
-tall, sterile males, with some feminine secondary sex characteristics
-muscular dystrophy
-results in wasting or disuse of muscles, often confined to wheelchair early in life
-PKU
-can result in mental retardation; retardation is preventable if mutation is identified in the first week
of newborn’s life
-symptoms of disorder can be prevented by a phenylalanine restricted diet
-cystic fibrosis
-results in an abnormal transmembrane protein, mucus accumulates in lungs and pancreas
-difficulty breathing, lung transplants have proved beneficial
-common among Eastern Caucasian populations and their descendents
-down syndrome
-individuals have an abnormal number of autosomes
-common chromosome mutation among the babies of older women, individuals have common facial
characteristics
34
Mutations
gene mutations
-occurs when the correct proteins is not expressed due to a mutation
-alters the proper functions of proteins
-has a broader range of effects because they mess up protein functions and there are so many proteins
with so many different functions
-may be autosomal- mistakes in the sequence of DNA of autosomal chromosomes
-ex: sickle cell anemia
-may be sex-linked-mistakes in the sequence of DNA of sex chromosomes
-ex: hemophilia
chromosome mutations
-occurs when too many or too few chromosomes are present in the zygote
-most likely to be lethal
-can cause there to be too much or too little information
Nondisjunction
-improper separation of homologous chromosomes during meiosis
-results in too many or too few chromosomes in daughter cells
-the Y chromosome contains a sex-determining region that is necessary for male sexual development
-no babies have been discovered that have been born without an X chromosome
-a female with the genotype XO has inherited only one chromosome and is sterile
causes of nondisjunction
-aneuploidy: cells that have too many or too few chromosomes are aneuploid
-monosomy: only one chromosome of a pair is present
-trisomy: 3 chromosomes instead of 2
-translocation: the relocation of a segment of DNA from one chromosome to another (basically when
chromosomes are “stuck” to one another)
12
13
karyotypes
-visible display or picture of all the chromosomes
-how biologists make it:
-they photograph cells during mitosis, when chromosomes are fully condensed and easy to see
-they cut out the chromosomes from the photographs and group them in homologous pairs
-allows diagnosis of chromosome disorders
-there may be too many or too few  aneuploid
-they may be “stuck” to one another  translocation
35
Genetic screening methods
-amniocentesis
-taking a sample of amniotic fluid during pregnancy to identify chromosomes and look for any
genetic defects of disorders in the baby
-chronic villi sampling
-taking samples of tissue from the placenta to identify chromosomes and look for any genetic
defects of disorders in the baby
-karyotyping
-taking a picture of the chromosomes in a cell
-PGD (preimplantational genetic diagnosis)
-the process:
-scientists take eggs from a female and fertilize them in a petri plate and wait until the zygote
develops into an embryo of 8 cells
-they then extract one of the cells (which doesn’t harm the embryo)
-they perform a DNA test to look for any genetic disorders
-they then implant the embryos that don’t carry disorders or mutations back into the female
Inheritance patterns
-heterozygote advantage
-heterozygous carriers can sometimes be immune to or resistant to another disease
-example: heterozygote carriers for sickle cell anemia are resistant to malaria
-genomic imprinting
-the activation or inactivation of certain genes that depends on the gene’s location on a
chromosome and its parental origin
-example: prader-willi syndrome
-genetic anticipation
-age of onset: when the severity of symptoms of a genetic disorder increases and symptoms show
up earlier with each generation
-example: Huntington’s disease
36
Lorenzo’s Oil
Application of scientific method
problem
-due to ALD< fatty acids build up in the brain and liquefy the myelin. How can scientists make a therapy
to reduce the fat levels? Lorenzo’s parents asked this question to themselves and several doctors
background research
-both of Lorenzo’s parents spend hours and hours in the library researching ALD and everything related
to it
hypothesis
-Lorenzo’s parents thought of many ideas to reduce Lorenzo’s fat levels like:
-eliminating the intake of fats in his diet
-putting oleic acid in his diet
-putting erucic acid in his diet
experiment
-Lorenzo’s parents first eliminated the intake of fats in his diet and then put first oleic and then erucic
acid into his diet. They waited for any changes.
data
-Lorenzo's parents observed Lorenzo’s levels as they tried each experiment. They kept track of the
information on graphs.
results
-the diet that was eliminated of fats raised Lorenzo’s levels
-the oleic acid only reduced Lorenzo’s oil by 50% percent
-the erucic acid reduced Lorenzo’s levels to normal
conclusion
-Lorenzo’s parents developed Lorenzo’s oil which is 4 parts oleic acid and 1 part erucic acid
-it lowers fat levels to normal
Characteristics of adrenoleukodystrophy (ALD)
-ALD: an inborn error of metabolism that harms the brain
-people with ALD don’t have the enzyme that should break down fatty acids  liquefies the brain
-it strips down the myelin of the neurons
symptoms
-hyperactivity
-withdrawal
-blind
-deaf
-mute
37
-coma
-paralysis
-death
prognosis
-all people with ALD die 2 years after diagnose
38
Chapter 18: Diversity and Variation and Prologue
-evolution: change over time
-the result of variations within populations over long periods of time
-it can result in:
-different forms of beaks (morphology)
-changes in use (bat wing vs. human hand)
-changes in behavior (feeding, mating, …)
-biologists observed that living organisms were different from the fossil organisms
-they then developed a theory called evolution that organisms change over time
-theory: explains current observations and predicts new observations
-evidence of observations of modern and fossilized organisms from all over the world supports evolution
The important people behind the theory of evolution
Jean Baptiste Lamarck
-thought living things constantly try to improve their form
-believed in use or disuse
-if an animal uses one parts of its body frequently, that part will become stronger and more
developed
-if an animal doesn’t use a part of its body, that part will slowly weaken, become smaller, and
disappear
-believed these modified structures are inherited by offspring
-however, his theory lacked the ability to predict results
August Weismann
-he tested Lamarck’s idea of inheritance of acquired traits by mating mice whose tails had been bobbed
-when the mice were mated, the offspring had long tails
-this disproved Lamarck’s theory
Charles Lyell and James Hutton
-lyell was a geologist
-promoted a hypothesis first developed by hutton
-he believed that the earth is much older than a few thousand years
-proposed that natural forces that existed in the past were the same as those of today
-he thought natural forces have shaped and continue to shape the surface of the Earth
-this is called uniformitarianism
Thomas Malthus
-thought that the size of a population is limited by the amount of resources and competition among
individuals for them
-said that the number of organisms increases geometrically (very rapid growth) and the food supply
increases arithmetically (not as fast)
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Alfred Wallace
-british naturalist
-in mid-1850s, he proposed an idea almost identical to Darwin’s theory of natural selection
-Darwin is given credit for the idea because of his extensive documentation
Charles Darwin and Natural Selection
history of Darwin
-had difficulty choosing a career
-was a contemporary of Abraham Lincoln
-was a part of an expedition around South America
-developed theory of evolution after returning to England
-spent 5 years on HMS Beagle as a naturalist, sketching and collecting plants and animals
-studied finches on the Galapagos Islands and noticed differences in the beaks of birds on different
islands
-wrote an essay of his ideas in early 1840s, but delayed publication because he knew his ideas would be
controversial
what also shaped Darwin’s ideas?
-charles lyell’s idea that the earth has undergone slow, uniform change  Darwin thought that if the
earth is under constant change, this change must affect the viability of plants and animals
-thomas malthus’ idea that the size of a population is limited by the amount of resources and
competition among individuals for them
-malthus said that the number of organisms increases geometrically (very rapid growth) and the
food supply increases arithmetically (not as fast)
-selective or artificial breeding: farmers selectively breed animals with the best traits
Darwin’s idea: natural selection
-variation exists within populations
-some variations are favorable  allows species to reproduce and gives them the potential to pass on
helpful traits
-not all young produced in each generation survive
-individuals that survive and reproduce are those with favorable variations = survival of the fittest
-survival of the fittest-organisms that inherit the “best” traits are the ones that survive
-they may pass their “good” genes on to the next generation
Evidence of evolution
fossils
-provide evidence of what earlier forms of the same animals or plants looked like
-can be used to show relationships
-the fossil record is often incomplete  not likely that organisms will become fossils
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biogeography
-two organisms that live in different geographic locations have similar traits
-ex: the flying squirrel lives in North America and the sugar glider lives in South America, but they are
very similar
morphology
-organisms that are related often demonstrate similarities
-ex: bears and wolves are more similar to each other than lizards, frogs and fish are more similar to each
other than beetle
homologous structures
-structures that are similar in structure, but serve different functions
-implies relatedness
-ex: hand vs. bat wing
vestigial structures
-structures that are inherited but are reduced in size and often unused
-suggests a common ancestry
-ex: leg bones in snakes and ear muscles in humans
embryos
-embryos of related organisms develop in similar ways
-ex: vertebrates
-pharyngeal pouches
-dorsal nerve cord (back)
-notochord (backbone on back)
-post anal tail
biochemistry
-all living things:
-use ATP (energy)
-code genetic traits in DNA
-make proteins with RNA
Gradualism and punctuated equilibrium
gradualism
-slowly…
-small genetic changes occur within populations, resulting in gradual changes
-this is what Darwin suggested  also called Darwinian evolution
punctuated equilibrium
-quickly!!!
-populations remain stable for long periods
-brief periods of rapid change within a short period
-some significant environmental change or a mutation can cause many things to change at once
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The species concept
-taxonomy: the theories and techniques of describing, grouping, and naming living things
-basically, taxonomy = scientific classification
-species: interbreeding populations of organisms that can produce healthy, fertile offspring under
natural conditions
-to be considered a species, the organisms must:
-be able to bread with one another and produce fertile offspring in nature
-ex: horse = a species
mule = not a species because it’s sterile
-humans = a species
-individual members of a species may look different from one another = variation
-natural selection acts on variation, resulting in changes in species or the evolution of new species
-variations in a population include:
-polymorphism- when two or more forms, or morphs, exist in the same population
-ex: male and females of the same species
-geographic variation- when a species occupies a large geographic range that includes distinct local
environments
-individual variation- occurs in all populations of organisms that reproduce sexually
-members of species may interbreed occasionally
-if the two groups fail to produce a significant number of hybrids, they remain separate species
-species remain separate from one another in three ways
1. potential mates don’t meet
-grizzly bear and polar bear: they live in different habitats and don’t meet in the wild
2. potential mates meet and don’t breed
-a giraffe and an ostrich meet but are too different to mate
3. potential mates meet and breed but don’t produce fertile or viable offspring
-a dog and a coyote mate but don’t produce fertile offspring
-the species concept doesn’t apply to organisms that don’t reproduce sexually
Linnaeus’ Classification System
-carolus Linnaeus “latinized” his name, karl linnea
-based on homologies and similarity of structure
-physical
-DNA
-used binomial nomenclature: a two-word specific name (Genus – species)
-used latin: understood all over the world
-the name is italicized when typed and underlined when written, and only the first word is capitalized
-it standardized scientific communication
-overcomes the use of common names
-taxon: the different groups that scientists classify organisms in based on common characteristics
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-there are 7 taxons (not including domain)
Levels of Classification
domain
-prokaryotes or eukaryotes
kingdom
-a group of related phyla
-there are 5 kingdoms today
phylum
-a group of related classes
-if an animal has a backbone, it is part of the phyla chordata
-many botanists group organisms into divisions instead of phyla
class
-a group of related orders
-ex: birds = aves
order
-a group of related families
family
-a group of related genera
genus
-a group of related species with many similar characteristics
species
-most specific group
-as you go from species to kingdom, the organisms that are grouped together share fewer
characteristics at each succeeding level
-at the species level, individuals are so alike they can interbreed
-organisms at the kingdom level share only a few common characteristics
-as you move from largest taxon to smallest taxon:
1. there are fewer organisms
2. they have more common characteristics
-the species describes the genus name
-ex: grizzly bear = ursa horriblus = horrible bear
Five Kingdoms
-as you move through the classification system from species to kingdoms, each level includes more
types of organisms
-the more types of organisms that a category includes, the less similar they are
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1. Monera/bacteria
-prokaryotes: unicellular or colonial
-reproduction by simple cell division
-include heterotrophs, photoautotrophs, and chemoautotrophs
-many types change their form of nutrition in response to changes in the environment
-bacterial taxomony relies heavily on comparisons of DNA sequences and the composition of cell
walls and membranes
-divided into two groups:
1. eubacteria
2. archaea
2. Protista
-mostly microscopic unicellular eukaryotes
-are descended from bacteria
-far more diverse than other kingdoms
-vary greatly in structure, reproduction, and lifestyle
-some switch from one form of nutrition in response to environmental conditions
-examples: algae (photoautotrophs), protozoa (swimming or creeping heterotrophs), slime molds
(funguslike protists), and others
3. Plantae
-photoautrophs
-multicellular eukaryotes
-developed from embryos
-have cellulose-containing cell walls
-their cells contain chloroplasts
-the bulk of the world’s food and much of its oxygen are derived from plants
-examples: mosses, ferns, conifers, and flowering plants
4. Animalia
-heterotrophs
-multicellular eukaryotes
-developed from embryos
-ranges in many sizes, these organisms are the most diverse in form of all of the kingdoms
-most reproduce sexually
-anthropods: animals that have exoskeletons and jointed legs, and may be the majority of all
multicellular species
-vertebrates: animals with a backbone
-most members of this kingdom are motile, or capable of locomotion, and have senses and nervous
systems
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5. Fungi
-most are decomposers
-some heterotrophs that absorb small molecules from their surroundings through their outer walls
-most are multicellular (with the exception of yeast)
-have cell walls composed of a thought carbohydrate called chitin
-they reproduce by forming spores, either sexually or asexually
-examples: yeasts, molds, bracket fungi, and mushrooms
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Chapter 7
Adaptations for Life on Land
-fossils and other evidence indicate that the first plants probably evolved from green algae
-the challenge of life out of water: loss of water
-so the first adaptations included a cuticle and protective structures for the gametes and embryos
-2 types of plants emerged:
1. vascular plants- had specialized vascular tissue and a tubing system
-the ancestors of all plants except mosses and their relatives
2. nonvascular plants- complex tissues didn’t evolve
-mosses and their relatives
-are restricted to damp environments and don’t grow very large
other challenges of life on land:
-soil contains water and minerals but the light and carbon dioxide needed for photosynthesis must be
obtained above ground
-vascular plants adapted by having an underground root system that absorbs water and minerals
and a different aerial system of stems and leaves that makes food
-the sections of roots that absorb water lack a cuticle
-root hairs greatly increase the root’s water-absorbing surface are
-how does a plant shoot stand upright
-lignin: a hard material embedded in the cellulose matrix of the cell walls which support trees and
other vascular plants
-xylem tubes: nonliving hollow tubes that carry water up from the roots
-phloem tubes carry sugars and the products of photosynthesis throughout the plants
Water Transport = xylem
-xylem consists of 2 types of water-conducting cells, plus strong weight bearing fibers
1. tracheids- have pointed ends and thick walls with pits that connect them to nearby cells
-water moves from cell to cell through these pits
2. vessel elements- wider, shorter, thinner walled, and less tapered
-the ends of vessel elements are perforated or missing and water can flow freely through these
openings
-columns of vessel elements form the xylem vessels that water moves throughout the plant in
how water is transported
- water is transported upward to reach the higher stems and leaves
1. cohesion-adhesion—capillary action
-the rise of water by capillary action isn’t very rapid
2. root pressure- high concentration of water from the soil moves into the roots
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3. transpiration- plants also lose a large amount of water through the stomates in their leaves when
the stomates open to exchange gases with the air
-this evaporation of water “pulls” water upward from the roots to the leaves
-it is the primary and most significant method of water transport in plants
Nutrient Transport = phloem
-in vascular plants, sugar and nutrients travel through phloem cells joined end to end
-sieve tubes = another name for phloem tubes
-tiny porous areas at the ends of phloem cells allow the contents of the cell to mix
-these porous areas look like tiny strainers, or sieves
-sugars and amino acids move through the phloem cells from the leaves to other parts of the plant
-the rate that this fluid moves is thousands of times faster than what diffusion can account for
-best explanation: pressure-flow hypothesis
-water and dissolved sugars move through the phloem from sources areas of higher pressure
(sources) to areas of lower pressure (sinks)
-sources (areas where photosynthesis is carried out) = leaves during spring and summer, and some
storage roots in early spring, cotyledons and endosperm during germination
-sinks (areas that need the products of photosynthesis) = found in the many areas of a plant where
waters and sugars are used, including food-storage areas and growing leaf buds, root tips, flowers,
fruits, and seeds
-the process
begins at a source, like a leaf, where photosynthesis occurs  the sugars are actively transported
into the phloem tubes from the mesophyll layer (where photosynthesis is carried out)  the high
concentration of sugars draws water into the phloem tubes  produces higher pressure which
forces the sugars to move toward the lower pressure at the sinks
-at a sink, active transport removes the sugars from the phloem to be used or stored
-as this occurs, water also leaves the phloem cells by osmosis, and most of it returns to the xylem
An overview of transport in plants
-plants take up water through roots only (not stomates)
-xylem transports water by capillary action
1) cohesion
2) adhesion
-high concentration of water from soil moves into the roots = root pressure
-no sugar in the roots because there’s no sunlight or chloroplasts  can’t carry out photosynthesis
 depend on leaves to make sugars
-all parts of the plant need oxygen for cellular respiration
-loose soil allows oxygen to reach the roots
-earthworms help to aerate soil
-cellular respiration = C6H12O6 + O2  CO2 + H2O + ATP (energy)
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-water is transported by xylem tubes to the leaves for photosynthesis
-photosynthesis
air
roots
CO2 + H2O
sunlight
chlorophyll
glucose
C6H12O6 + O2
- C6H12O6 is transported throughout the plant by phloem
-plants also lose a large amount of water through the stomates in their leaves = transpiration
-this evaporation of water “pulls” water upward from the roots to the leaves
-it is the primary and most significant method of water transport in plants
More about plants (from the lab we did)
-plants and animals have a layer of tissue called the epidermal layer (like the skin)
-plants have stomata, special pores that allow gas exchange
-guard cells surround gas exchange and regulate gas exchange by opening and closing stomata
-guard cells contain chlorophyll
-when there is a lot of water in the environment, guard cells swell up and open stomates. This
allows carbon dioxide to diffuse in and water vapor and oxygen to diffuse out
-when there is a low amount of water in the environment, guard cells shrink and close stomates to
minimize water loss
-stomata would be closed during the hottest and sunniest time of day to try to minimize water loss
-the lower epidermis has more stomata to reduce transpiration, or water loss. The lower epidermis is
less exposed to sun and wind which both increase transpiration
-the number of stomata tells you a lot about a plant
-high amount of stomata = fast growth and wet climate
-lower amount of stomata = lower rates of photosynthesis and growth; adaptations for dry weather
functions
cutin = main component of the cuticle
cuticle = waxy surface on the top of leaves that blocks water from penetrating, forcing gas exchange to
occur in the stomata and directs water to the roots
upper epidermis = protection
lower epidermis = protection and has stomates
palisade layer = where photosynthesis is carried out and maximizes absorption of sunlight
spongy layer = where photosynthesis is carried out and provides air space for carbon dioxide to come in
mesophyll layer = palisade layer + spongy layer  photosynthesis
stomata = allows gas exchange in plants
guard cells = regulate water loss and gas exchange; open and close stomata
xylem = carry water and minerals up from the roots to the leaves for photosynthesis
phloem = actively transport sugars and organic nutrients of photosynthesis throughout the plant
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Circulatory Systems
-unicellular organisms, like paramecium:
-no specific transport structures
-food vacuole
-the food in the vacuole is broken down by enzymes
-the food then diffuses into the cytoplasm
-multicellular microscopic organisms, like hydra
-no specific transport structures
-simple diffusion
-fluid containing food, oxygen, and carbon dioxide passes into and around its body as the hydra
moves
-its tentacles catch the food and the food goes in the mouth into the gastrovascular cavity where it
is broken down. It then diffuses into the endoderm and ectoderm
-insects, crabs, and other arthropods, like grasshoppers
-open circulatory system
-there is no separation between blood and other intercellular fluid
-transports hemolymph, not blood
-the movement of the insect moves and circulates the fluid
-there is no pumping mechanism to keep the fluid flowing and moving
-organisms with this kind of system tend to be smaller or more sluggish because it’s less efficient
-insects distribute oxygen through microscopic air ducts with branches that reach every part of
their body which works well because of their small size
-invertebrate organisms, like earthworms
-closed circulatory system
-blood is confined to vessels
-major vessels branch into smaller vessels that carry blood to or from the various organs
-blood is transported in blood vessels by aortic arches also known as “hearts” to circulate the blood
-more efficient at delivering food and oxygen
Circulation in Vertebrates
-closed circulatory system called the cardiovascular system
-consists of a heart with chambers, blood vessels, and blood
the heart
-has chambers
-one or more atria (singular: atrium)- chambers that receive blood returning to the heart
-one or more ventricles- chambers that pump blood out of the heart
3 types of blood vessels
1. arteries- carry blood away from the heart
2. veins- carry blood to the heart
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3. capillaries- connect arteries to veins
Types of hearts
fish
-2 chambers
-1 atrium
-1 ventricle
-called a single loop circulation
amphibians and reptiles
-3 chambers
-2 atria
-1 ventricle
*least efficient:
-because there’s only one ventricle, deoxygenated blood comes in through one atrium and oxygenated
blood come in through the other atrium into the same ventricle
-deoxygenated blood and oxygenated blood mix  these organisms’ blood is partially deoxygenated
-because organisms need oxygen for cellular respiration (which produces energy), these organisms don’t
have much energy
birds and mammals
-4 chambers
-2 atria
-2 ventricles
-the septum divides the two ventricles, and allows the deoxygenated blood to be pumped out into the
lungs
the path of the blood:
-deoxygenated blood enters the right atrium and flows into the right ventricle
-it goes to the lungs through the pulmonary artery where it is enriched with oxygen
-the newly oxygenated blood comes back to the heart through the pulmonary veins
-it enters the left atrium and flows into the left ventricle
-it then leaves the heart through the aortic arch and flows to the rest of the body
Arteries, Veins, and Capillaries
arteries- carry blood away from the heart
-carry oxygenated blood (which is bright red)
-larger in diameter
-thicker – more smooth muscle tissue that allows blood vessels to contract and move blood
-able to constrict on their own
-found deep (closer to the bone)
-coronary arteries: carry blood to the heart
-pulmonary arteries: carry blood to the lungs from the heart
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-biggest artery = aorta – leads from the heart and supplies blood to the body
-large arteries have walls made up of smooth muscle and other elastic tissue
-when the heart contracts (systole): it forces blood into these arteries under high pressure,
stretching their walls which allows more blood to enter and prevents the pressure from being too
great
-during the relaxed phase of the heartbeat (diastole): the stretched artery walls contract, helping to
push the blood along and maintain blood pressure
-signals from the nervous system can cause smaller arteries to contract and expand
veins- carry blood to the heart
-carry deoxygenated blood
- smaller in diameter
-less smooth muscle tissue
-superficial (closer to the surface)
-valves prevent blood from flowing backwards—blood is flowing upwards, against gravity
-lower pressure
-veins have thinner walls with less muscle and elastic tissues than arteries
capillaries- connect arteries to veins
-drops of oxygen and picks up carbon dioxide
-thinnest, tiniest tubes- can be 1 cell layer thick
-connect arterioles to venuoles = where the blood deoxygenates
-found everywhere in the body
-thin capillary walls allow chemicals to be exchanged between the blood
-thin capillary walls also allow the intracellular fluid surrounding the cells and oxygen and carbon
dioxide to be exchanged with air in the lungs
-blood flows from:
the heart
arteries
High pressure
arterioles
capillaries
venuoles
veins
the heart
Lowest pressure
Highest pressure
Heart Anatomy
-the circulatory system is made of 2 parts:
-cardiovascular system- circulates the blood
-lymphatic system- removes foreign substances
-oxygen, carbon dioxide, nutrients and waste are transported by the body’s circulatory system
-93,000 miles of blood vessels in the human body
-36 gallons or 6,000 quarts of blood in the body
-the heart is the size of your fist
-pericardium: the membrane that surrounds and protects the heart
-tough
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-a little translucent
-pulmonary circulation: supplies blood to the lungs
-systemic circulation: supplies blood to the rest of the body
-autonomic system- the nervous system that controls the heartbeat
-the cardiac cycle: each heartbeat is a sequence of muscle contraction and relaxation
-in each cycle, the four chambers of the human heart go through phases of systole and diastole
-diastole: heart at rest
-the ventricles are filling
-systole: heart at work pumping blood
-ventricular contraction
-the atria contract slightly before the ventricles
-when the atria are relaxed and filling, the ventricles are also relaxed
-as the pressure rises in the atria, the valves between the atria and ventricles (AV valves) are forced
open and the ventricles start to fill
-then the atria contract (atrial systole), forcing additional blood into the ventricles
-next, the ventricles contract (ventricular systole), causing the AV valves to snap shut and the pressure
inside the ventricles rises sharply
-valves to the aorta and the pulmonary arteries open and blood flows out of the heart
-then the ventricles relax and the cycle starts again
-AV valves prevent blood in the ventricles from backing up into the atria
-leaks in these valves cause the condition known as heart murmur
-although the heartbeat starts in the heart itself, changes in the rate of the heartbeat are controlled by
nerves outside the heart
Blood Pressure
-a healthy blood pressure is maintained through complex interactions involving hormones and the
nervous, excretory, and circulatory systems
-nerves connect pressure receptors in the aorta and the artery leading to the brain
-other cardiac things respond to sensory input like emotions and chemical input like carbon dioxide
-when someone’s blood pressure falls below normal, for example due to danger or exercise, the brain
sends signals to increase blood pressure
-to increase blood pressure:
-increase the heart rate and constrict the blood vessels
-to decrease blood pressure:
-decrease the heart rate and don’t constrict the blood vessels
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-tissues that are most important during activity, like the heart and skeletal muscles, receive more
oxygen and nutrients
benefits of exercise that move large skeletal muscles
-brings more oxygen to muscles
-increases the flow of blood to the heart
-reduces the oxygen need of muscles
-reduces cholesterol and blood pressure
-helps with weight loss
hypertension
-hypertension: having blood pressure higher than normal
-20% of the adult population has hypertension
-it causes serious health problems, even death
-it forces the heart to work harder which can damage heart muscles
-it can damage blood vessels in the brain so they rupture which can cause a stroke
-it contributes to atherosclerosis
-its exact causes aren’t known
-it can be prevented or controlled by medication, regular physical examinations, proper diet, and
exercise
-1 in 5 Americans is most likely to die of heart disease
Composition of Blood
-blood is the only fluid tissue in the body
-total volume of blood in the body = 5-6 quarts
-blood is made of 4 parts:
erythrocytes- red blood cells
-contains hemoglobin
-hemoglobin binds to oxygen
-oxygen is released from blood when the blood passes through capillaries
-oxygen diffuses out into surrounding tissues
-carbon dioxide is transported by the blood plasma back to the lungs
leukocytes- white blood cells
-protect against foreign substances
-defend again bacteria and viruses
-an infection results in more white blood cells
thrombocyte- platelets
-allows the blood to clot or coagulate
-platelets become “sticky”
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-fibrin (a protein produced by a series of chemical reactions) forms a network of fibers to trap red blood
cells
-abnormal clotting when blood flow to heart is blocked = heart attack
-abnormal clotting when blood flow to brain is blocked = stroke
plasma
-the “watery” part of the blood
-it transports blood cells (red blood cells, white blood cells, and platelets)
-it helps to regulate body temperature
-consists of water, dissolved ions (electrolytes), amino acids, sugars, and hormones
-transports carbon dioxide back to the lungs
-maintains the pH of the blood and water balance in the body