Download DNA and Protein Synthesis

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Biology Unit #4: Chromosomes, DNA & RNA, Protein Synthesis, Gene Regulation, and Mutations
I. Chromosome Structure (Eukaryotic)
DNA is a double (2) stranded molecule that is helical (twisted) in shape.
Chromatin – A combination of DNA and proteins called histones. The DNA-histone complex is loosely coiled and is
not visible with a light microscope. DNA-histone complex is in chromatin form during interphase of a cell’s life cycle.
Q: What is the benefit of having DNA in Chromatin form?
Chromosomes – Tightly, supercoiled DNA-histone complex. After DNA has been replicated (copied) during interphase,
the two copied/identical and supercoiled DNA-histone complexes called chromatids are united by a centromere.
Q: What is the benefit of having DNA in Chromosome form?
In all sexually reproducing organisms chromosomes occur in pairs (1 from the mother and 1 from the father.) These pairs
are called homologous chromosomes. Homologous chromosomes carry directions/alleles for determining the same
traits, like eye color but they do not always carry the same version of directions/alleles for the same trait.
Q: What is the benefit of having lots of variation within a species?
 To determine the number of chromosomes a cell has, count the number of centromeres not the DNA strands.
 Every species/organism has a characteristic # of chromosomes in each cell.
 Does the number of chromosomes determine how complex the organism is? __________________
Organism – Kingdom
All Bacteria
Yeast – Fungi
Bread mold – Fungi
Potato – Plant
Tobacco – Plant
Corn – Plant
Adder’s Tongue Fern – Plant
Chicken
Dog
Human
Chimpanzee
Body/Somatic Cell (2n)
1
32
8
48
48
20
1,262
78
78
46
48
Sex Cell/Gamete/Eggs & Sperm (n)
0
16
4
24
24
10
631
39
39
23
24
Cell Types and their Chromosome Number
Cell type w/examples
Cell type alternate names
Sets of chromosomes per cell
Naming sets of chromosomes
or
Body Cells
kidney, bone, liver, muscle
*
Sex Cells
eggs, sperm
*
or
*
 Are there homologous chromosomes in sperm and egg cells?
________________
Skin and spleen cells? ____________
Karyotype – Picture of
chromosomes taken in metaphase
that have been stained, blown up in
size and homologues paired up
Sex Chromosomes _________________
Autosomes _______________________
What distinguishes chromosomes?
 Size (# of nucleotides)
 Centromere location
 Staining pattern
II. DNA Structure
Function – DNA (DeoxyriboNucleic Acid) holds directions in the form of a four letter code to make RNA (RiboNucleic Acid),
which in turn build proteins. Proteins are vital to most of our bodily functions and to our body’s structural needs.
Structure – DNA is a macromolecule made up of smaller molecules or monomers called _____________________________.

Phosphate

Deoxyribose (5 carbon sugar)

Nitrogen Containing Base (4 kinds)
(A) Adenine – double ringed
 Purines
(G) Guanine – double ringed
(T) Thymine – single ring
 Pyrimidines
(C) Cytosine – single ring
DNA is a double stranded molecule with a helical/spiraled
shape. The deoxyribose sugars are bonded to phosphates along
the outside of the molecule and bases toward the inside of the
molecule. The 2 strands are then hydrogen bonded to each
other via their bases. Adenine always double hydrogen bonds
to Thymine and Guanine always triple hydrogen bonds to
Cytosine. This bonding of A=T and GC makes the strands
exactly opposite or complementary. Complete the bonding and
base pairing below.
P
Strand #1
P
S
P
S
A
P
S
A
P
S
C
P
S
A
P
S
T
P
S
G
P
S
G
P
S
A
P
S
T
P
S
T
S
C
C
Strand #2
The structure of DNA was solved together by Francis Crick (English) and James Watson (American) in 1953. They used
research skills, communication, and model building to make this one of the most important scientific discoveries. Watson
and Crick used the hard work of the following scientists:
(a) Alexander Todd to determined the parts of a nucleotide: ______________, _________________, & ______________
(b) Rosalind Franklin & Maurice Wilkens ( X-ray crystallography) to determine the general position of nucleotides and
the number of DNA strands
(c) Linus Pauling and Jerry Donahue to determine bond types and angles
(d) Erwin Chargaff to determine base pairing rules (A with T, G with C)
Use the space below to draw and color code a portion (2 base pairs or 4 nucleotides) of an unwound DNA molecule.
Adenine
A
Light blue
Guanine
G
Dark Green
Use Black for Hydrogen bonds (= or ≡).
Use Light Green for Phosphodiester bonds.
Use Brown for glycosidic bonds.
Cytosine
C
Purple/Violet
Shade behind the backbone of the molecule with yellow.
Thymine
Phosphates -
Deoxyribose
Sugars
T
Orange
P
Dark Blue
Circle a Nucleotide with a black circle.
Circle the Purines with a pink circle.
Circle the Pyrimidines with a grey circle.
DS
Red
III. DNA Replication – Occurs during interphase of a cell’s life cycle, DNA replication is making identical copies of chromosomes.
Step 1: Many DNA Helicase enzymes attach themselves to, and cut hydrogen bonds between bases. Why are so many DNA Helicase
enzymes needed?
Step 2: With H-bonds cut, the 2 strands of DNA are now separating. Free-floating nucleotides within the nucleus now attach to their
complement nucleotide, AT & GC. Where do the “free-floating” nucleotides come from to form a new DNA molecule?
DNA Polymerases are the enzymes that will help bond the new nucleotides to the old nucleotides (original strand), they also help the
new nucleotides to bond to each other.
Use the sequence of DNA nucleotides labeled original strand to draw and color (original one color and the new strands another color)
the DNA Replication process.
Original Strand - Before
P
Step #1 - During
Step #2 - After
P
S
C
S
P
P
S T
S
P
P
S
A
S
P
P
S
G
S
Q: Why is DNA replication said to be “semi-conservative?
Errors in base pairing are rare, about 1 in every billion. These errors in base pairings, thus changing the sequence of DNA is termed
mutation. The agents that cause mutations are termed mutagens (cigarette smoke & tar, asbestos, radiation, etc.).
Gene – A specific sequence of DNA nucleotides/bases which codes for the making of specific proteins ( 30,000 in humans).
IV. RNA Structure and Function
Function – Builds proteins.
Structure – RNA is a macromolecule made
of small molecule called…___________________.

Phosphates

Ribose Sugars

Nitrogen Containing Bases (4)
(A) Adenine – double ringed
 Purines
(G) Guanine – double ringed
(C) Cytosine – single ring
 Pyrimidines
(U) Uracil – single ring
RNA is a single stranded molecule with 3 general shapes, thus 3 general functions.
Messenger RNA (mRNA) – A linear/straight RNA molecule that carries a complementary copy of a gene. The
complementary copy of a gene (found on DNA) is called the genetic code (found on mRNA). The genetic code is read 3
bases at a time (AUG, GGA, etc.), which are called codons.
Ribosomal RNA (rRNA) – A folded, globular shaped molecule. rRNA and some proteins are the components of a
ribosome.
Transfer RNA (tRNA) – A folded RNA molecule that is t-shaped. At the top of the tRNA molecule is the site where
amino acids (protein monomers) attach. At the bottom of the tRNA molecule is the site where the genetic code is read.
The complement sequence, read 3 bases at a time, reads the mRNA (codon) and is called the anticodon (tRNA).
Bonding DNA to RNA, and RNA to RNA follow the complementary bonding of DNA to DNA with one exception (U for T). AU,
TA, UA, CG, and GC. Use the sequence of DNA to make a complementary copy of RNA.
DNA 
A
G
C
T
T
C
G
A
G
G
C
A
T
T
A
RNA 
What are three ways in which DNA is structurally different from RNA?
1.
2.
3.
V. Protein Synthesis (Transcription and Translation) – View genetic code on page 6 and protein synthesis pictures on
page 7.
1. Transcription – Process of making all 3 forms of RNA. RNA shape, thus its function, is determined by it base
sequence.
 The enzyme RNA Polymerase attaches itself to the hydrogen bonds of a DNA molecule at the beginning of a
gene. RNA polymerase breaks the hydrogen bonds opening the DNA molecule and exposing the bases of a
gene.
 RNA Polymerases then help to form hydrogen bonds between a strand of DNA and free-floating RNA
nucleotides.
 There is no Thymine in RNA, Uracil is substituted.
 Remember: bonding is complementary A___, T___, G ___ , C ____.
 RNA Polymerases then help to make sugar to phosphate bonds between newly formed RNA nucleotides.
 After copying the gene, RNA detaches itself from the DNA molecule and the split strands of DNA now reattach.
 After RNA detaches from the DNA molecule it must
be modified/changed to become functional/usable.
Enzymes remove portions of the RNA molecule before
it is structurally the correct size and shape. The
portions of RNA that are transcribed but not translated
are called introns (stays in the nucleus) and the
portions of RNA that are transcribed and translated
(exit the nucleus) are called exons.
2. Translation – The process of RNA making proteins from the encoded directions received from DNA (genes).
 After mRNA is made it travels through the nuclear membrane to a ribosome located in the cytoplasm and on rough
ER’s.
 Once the mRNA reaches a ribosome the 1st codon will be read (AUG is always the 1st codon that is read).
 A codon codes for a specific amino acid or gene terminator, a codon may only code for 1 amino acid.
 There is redundancy in the code, meaning that more than one codon can code for the same amino acid.
 Why do you think that scientists guessed that the genetic code was read 3 bases at a time?
Page 6
Because AUG is the first codon read while making a protein, then the 1st amino acid brought to the ribosome by tRNA is…
What is the anticodon on the tRNA that will carry the 1st amino acid?
 After methionine is brought to the ribosome the next codon is read. Upon reading the next codon, a tRNA will
bring the next amino acid which is floating in the cytoplasm near the ribosome.
 After the 1st two tRNA’s are attached to the mRNA, a peptide bond will form between their amino acids.
 After the peptide bond is made between the 1st two amino acids, the 1st tRNA will drop off and seek another
methionine.
 The ribosome will continue to build a protein in this manner until it reaches a stop or terminator codon, signaling
the end of the polypeptide/protein. After reaching a stop codon the protein will be released. What happens to the
protein now?
a)
b)
c)
AA= Amino Acid
- = Peptide Bond
AA-AA-AA-AA-AA-AA-AA = Polypeptide
AA-AA-AA-AA-AA-AA-AA-AA-AA-AA-AA-AA-AA-AA-AA-AA

AA-AA-AA-AA-AA-AA-AA-AA

AA-AA-AA-AA-AA-AA-AA-AA
The sequence of _________determines the sequence of ________,which determines the sequence of
________________ ________________.
The # and sequence of amino acids determines the size and shape of a ___________________.
The ____________ & ________________of a protein determines the ____________________ of a protein.
V. GeneRegulation/Expression
Q: What is a gene?
If an organism possesses 30,000 different genes, about how many of
them are found in each cell? Why?
1. Gene Regulation in Prokaryotes (Kingdom Monera – Bacteria)
Gene Types:
a) Structural Genes – Produce proteins that perform daily functions
(enzymes, hormones, antibodies, etc.).
b) Regulatory/Control Genes – Regulate or control the
expression/turning on and off of structural genes by producing a
repressor protein. There are many repressor proteins to control the
many genes possessed by an organism. When a specific regulatory
gene produces a specific repressor protein it will turn off a specific
structural gene. When a specific regulatory gene does not produce a
specific repressor protein it will allow that specific structural gene to
remain on and produce a specific protein.
2. Gene Regulation/Expression in Eukaryotes (Kingdoms – Protista, Fungi, Plants, and Animals)
a) In eukaryotic gene regulation structural and regulatory genes are used but it is much more complicated and not
fully understood.
b) Gene regulation not only involves control genes but is also dependent on the amount of DNA coiling
(nucleosomes), explain?
c) Eukaryotic gene regulation differs in that
a. a nuclear membrane is involved
b. multiple chromosomes are involved
c. multiple genes may control a single trait.
Q: What are Hox genes and why are they significant/important?
Fill in the Blanks: Complete the following table for the DNA and mRNA sequenes, the anticodons, and their amino acids. Use the
genetic code of life (on the back of this page) to help you answer these questions.
VI. Mutations - Any change in the sequence and/or amount of DNA that a cell possesses.

Somatic Cell Mutations –

Germ/Sex Cell Mutations –
Types of Mutations:
1. Gene or Point Mutatations – Mutations that only affect one gene.
2.
Normal Codon Sequence
THE CAT ATE THE RAT
a) Addition or Duplication –
THE CAT ATE THE THE
b) Subtraction or Deletion –
THE ATE THE RAT
c) Substitution or Missense –
THE COT ATE THE RAT
Chromosomal Mutations – Mutations that affect many genes on one or more chromosomes.
a) Deletion b) Translocation –
c) Inversion –
d) Nondisjunction –