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Biology Summary
Chapter 2
2.1
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to sustain life, cell must create and maintain molecules and structures that
then perform the essential tasks to perform cell functions including
o obtain food and energy
o convert energy into a form that works within a cell
o construct and maintain the molecules that make up cell structures
o carry out chemical reactions
o eliminate wastes
o reproduce
o keep records of how to build structures
Prokaryotes are cells that lack a true nucleus, instead, the DNA in these cells is
concentrated in nucleoid
Eukaryotes are cells containing a true nucleus and other organelles.
- larger
- contain complex internal structure
Organelles are specialized structures within a cell with specific functions
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a great deal of diversity exists among eukaryotic cells
organelles in a eukaryotic cell divide its interior into compartments
allows different chemical reactions taking place at once without interfering
with one another
many organelles contain highly folded membranes that increase the
surface area on which chemical reactions can be co-ordinated
and increases overall rate of reaction within the cell
Freeze Fracture Technique
- technique used by scientists to expose the nucleus for study
- provides valuable details about organelle and membrane structure
- could view two layers of the double membrane around nucleus
Electron Micrograph
- a close up scan of the organelle
- could show the nuclear pores and reveal their flower-like structure
Drawing
- artist render information from electron microscope
- compose a 3-D drawing of nuclear envelope
2.2
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almost all cell processes require proteins
proteins make up about half of the dry mass of cellular material
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many proteins function as enzymes
ie blood protein hemoglobin carries oxygen and carbon dioxide
cells produce proteins only in the amounts and at the times required
Protein synthesis is the process of making proteins which involves transcription
and translation.
1. Transcription occurs in nucleus
- cell transcribes (copies) the coded information from the gene of DNA
- cell must unwind and unzip that section of DNA and make an RNA copy of
it
- transcription is the process of making a copy of the information along
one strand of DNA to produce a strand of mRNA
2. mRNA moves into cytoplasm
- mRNA carries the coded message from DNA in nucleus to ribosomes in
the cytoplasm
3. Translation starts when mRNA attaches to a ribosome
- Translation is the process of using the coded mRNA instructions for a
sequence of amino acids to produce a polypeptide that take place on a
ribosome
- Ribosome then translate mRNA and attach mRNA to either a cytoplasmic
ribosome or to a ribosome attached to the endoplasmic reticulum
4. tRNA brings amino acids to the ribosome
- dissolved amino acids in the cytoplasm must be transferred to ribosome
for assembly into a polypeptide
- tRNA, transfer RNA recognizes one amino acid and attaches it to one side
of itself
- on other side of tRNA molecule, 3 nucleotide bases match one of the
triplet codes on the mRNA
5. An incoming tRNA positions its amino acid to join the polypeptide
chain
- tRNA carrying the next amino acid in the mRNA code forms a temporary
bond with the mRNA at the ribosome
- this places the amino acid in the correct position to form a peptide bond
with the amino acid on tRNA molecule already at the ribosome
- 15 amino acids are added to polypeptide chain per sec
6. An outgoing tRNA releases its amino acid and detaches from the
mRNA
- A ribosome has room for only 2 tRNA molecule at a time
- When ribosome moves along the mRNA to the next coding unit, outgoing
tRNA transfers the polypeptide chain to the other tRNA
- Frees up space for a new tRNA molecule at the ribosome
- The outgoing tRNA can now collect another amino acid
7. Translation ends when a ribosome reaches a “stop” instruction
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When ribosome reaches the “stop” codes at the end of an mRNA strand, it
releases the complete polypeptide
Then ribosome separates into its subunits which detaches it from the
mRNA
Polypeptide must still complete its folding process before becoming a
finished protein
process of transcription and translation in prokaryotes and eukaryotes
follow similar basic steps
but protein synthesis in prokaryotes is simpler
prokaryotic ribosomes are smaller than eukaryotic ones, lie close to DNA,
so the beginning of an mRNA strand can attack directly to a ribosome
while the rest of strand is still being transcribed
allows prokaryotes to produce proteins rapidly
each lysosome in animal cell or vacuole in plant cells contain over 40
different digestive enzymes
after the lysosome leaves Golgi body, its membrane actively pumps in
hydrogen ions to make its interior environment more acidic which activates
the lysosomal enzymes
when active, these enzymes can break apart macromolecules in a stepby-step process
Lysosomal digestion is the step-by-step process of breaking
macromolecules within lysosomes, also called intracellular digestion
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down
after a cell engulfs materials by endocytosis, a lysosome fuses with the
ood vacuole formed to fill the vacuole with digestive enzymes and break
down the captured material
a lysosome fuses with and digests worn out organelles
recycle their components back to cytoplasm
enzymes make possible reaction that would otherwise not proceed
Enzyme is a protein that functions as an organic catalyst that helps a particular
reaction go forward without being used up in the process
2.3
cell makes a different enzyme for each reaction it requires
an enzymatic reaction may either combine molecules to produce a new
product or break a molecule into smaller parts
enzyme’s shape allows its substrate to attach at the active site
chemical bonds within a substrate will then be broken
then the enzyme releases the products and can start the process again
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a multicellular organism contains a large number of different kinds of
specialized cells
Tissue is a group of specialized cells that have the same structure and perform
the same function
Ie muscles
Organ is a group of different tissues working together
Ie leaf of a plant
Heart muscle cells
- pump blood throughout the body
- small size of heart muscle cells gives them a large surface area,
increasing their access to critical materials
- have a branched shape that allows them to form an interconnected
network of cells
- can conduct electric impulses and contract in unison
- contain many large mitochondria to power their action
- contain actin and myosin filaments that allow them to contract
Parietal cells
- within indentations in the lining of stomach (gastric pits) cells secrete the
juices necessary for digestion
- parietal cells there produce hydrochloric acid
- activates an enzyme secreted by other cells lining the gastric pit and
allows digestion
- parietal cells contain tiny canals that run from cell membrane facing the
gastric pit deep into cytoplasm
- each canal lined with small extensions of cell membrane called microvilli
- with little increase to cell size, the folded fringe of membrane maximizes
the surface area for pumping hydrogen ions out into the canals
- requires large number of mitochondria
Podocytes
- cells excrete toxic nitrogen-containing waste in the form of ammonia,
which the liver converts to less toxic substances: uric acid or urea
- kidney function is to cleanse the blood of this nitrogen waste
- podocytes cells act as main filtration barrier in nephron of the kidneys
- has long thin processes that interlock with the process of another
podocyte around the capillaries entering the kidneys
- arterial blood pressure pushes small molecules from the capillaries into
the kidney through think membranes between prodocyte processes
- podocytes keep blood cells, platelets, and proteins from leaving the blood
- before urine leaves kidneys, other specialized kidney cells extract amino
acids, glucose, and required salts from the liquid
Squamous epithelial cells
- in lungs, extremely thin, flat cells line the tiny sacs (alveoli) where gas
exchanges take place
- lies directly against the thin cells from capillary walls
- provide shortest distance possible (1m) for oxygen to diffuse into and
carbon dioxide to diffuse out of body
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stem cells are blank slate of the human body
undifferentiated (nonspecialized) cells that can give rise to any type of cell
until they differentiate, stem cells can reproduce themselves indefinitely
ie rapidly dividing cells of a week-old embryo
people retain a limited number of stem cells
the body uses reserves of stem cells to replace worn-out or damaged cells
mainly found in bone barrow, blood, muscle tissue, lining of digestive tract,
brain, and retina of the eye
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proper development and maintenance of all tissues requires that some
cells be removed or replaced
Apoptosis is a process in the development and maintenance of all tissues in
which some cells turn on an orderly self-destruct process (programmed cell
death)
- most cells with DNA damage and many infected with viruses die by
apoptosis
- when a cell dies dies from injury, the cell contents scatter into its
environment
- in body, this leads to inflammation of the area
- in apoptosis, a series of enzyme reactions degrade the contents of a cell
- cell shrinks and small bulges appear along cell membrane
- special phagocytotic cells engulf and digest these cell fragments
- phagocytotic cells also release chemicals that inhibit inflammation
- some cells with damaged or defective DNA don’t make the correct
chemicals to induce apoptosis
- failure of apoptosis can result in cancer ie leukemia
- too much apoptosis can lead to degenerative diseases ie muscular
dystrophy
2.4
Finding New Cancer Treatments
- investigators map the process by which apoptosis works, looking for ways
to activate the apoptotic mechanism in tumour cells
- possibility that cancer cells could be induced to self-destruct may provide
basis for various treatments
- look at how treated cells in a culture die
- track this by tagging cellular structures sensitive to changes that take
place during apoptosis with fluorescing dyes
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so can see how a particular treatment is working
newly discovered that some cancer cells don’t produce an important cell
membrane receptor that allows the killer cells of the immune system to
signal a damaged cell to begin apoptosis
Insulin
- diabetes caused by deficiency of insulin, because the islet cells in
pancreas have been damaged or destroyed
- or by inability of cells to respond to insulin
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when eating, the cells in intestines transfer nutrients into blood stream
when blood glucose level rises, healthy islet cells synthesize quantities of
insulin and secrete it into blood stream
insulin is a hormone that binds to cell membrane receptors, mainly on
muscle and liver cells
this signals the cells to take up glucose and amino acids
also causes protein synthesis to start
as soon as blood glucose levels fall, insulin production shuts down
cells then have stored the nutrients they need until the next meal
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without insulin, when cells fail to receive its signal, glucose and amino acid
transport into cells and protein synthesis within cells shut down
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body uses lipids as an alternative energy source to glucose
large quantities of lipid products start circulating in blood
some of these form deposits in blood vessels, impeding circulation, others
are acidic and damaged tissues
blood contains so much glucose that kidney cells can’t filter it back into
blood
glucose in urine draws water with it by osmosis, causing cells to become
dehydrated and circulation to collapse
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Biotechnology and human insulin
- huge demand for insulin
- insulin used to be extracted from the islet cells of beef cattle or pigs
- animal insulin similar enough to human insulin that it can function, but will
develop allergic reaction
- insulin biotechnology involves the use of living organisms to manufacture
products for humans
- pharmaceutical industry genetically engineers bacteria to manufacture
human insulin
- bacteria given DNA instructions for making human insulin molecules and
then manufacture insulin along with other proteins they need
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on-time insulin delivery
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regardless of their source of injected insulin, diabetics have to deal with
swings in blood sugar levels
use computerized “smart” pumps to test a diabetic’s blood level and
automatically dispenses the correct amount of insulin
viral vector technology
splice DNA instructions for making a molecule similar to insulin into the
DNA of a harmless virus
when virus enters liver cells, the cells begin to make the desired insulinlike molecules
engineered insulin only 40% as potent as natural insulin, but sufficient
enough to control blood glucose levels
Newer forces driving research
- AIDS (acquired immunodeficiency syndrome) and hepatitis C. are
examples of recently identified diseases
- AIDS caused by HIV (human immunodeficiency virus)
- Hepatitis C caused by HCV (hepatitis C virus
- HCV transmitted through direct contact with infected blood
- Spread among people who share injection needles
- Damages liver cells
- Symptoms include fatigue, jaundice (yellowing of skin or eyes), nausea,
hair loss, and build up of toxins in blood
- Can lead to chronic inflammation of liver, liver cancer, death
- Need liver transplants