Biol 12: DNA and Protein Synthesis Review ANSWERS
Review Questions:
1. Where are the genes found in a cell? Name the two biomolecules found in
chromosomes.
2. List the 3 subunits of every nucleotide found in nucleic acid. What are the purine an
pyrimidine bases?
3. The 2 strands of DNA twist about one another to form a
double (righthanded!) helix with the 2 strands held together by Hydrogen bonds between he purine
and pyrimidine bases.
4. Which complementary bases pair together in DNA? How does the structure of
unwound DNA compare to that of a ladder?
5. Complete the following table by comparing cellular DNA to cellular RNA:
DNA
RNA
Function:
stores Genetic information
copies genetic information
Sugar:
deoxyribose
ribose
Bases:
ATCG
AUGC
Strands:
double
single
Helix:
yes
no
6. List the 3 basic functions that DNA, as a hereditary material, must be able to do.
7. What is the function of helicase and DNA polymerase? List the steps required in DNA
replication.
8. Why is DNA replication said to be semiconservative? Which enzyme “proofreads” the
replicated DNA?
9. What is the difference between transcription and translation?
10. Name the specific type of RNA that is used to produce the correct order of amino
acids in a polypeptide.
11. How many bases are used in the genetic code? Is the genetic code a doublet or a
triplet code?
12. Define a codon. How are the 3 different types of codons used?
13. Is the genetic code considered essentially universal?
14. During transcription, a segment of DNA unwinds and complementary free
nucleotides pair with the DNA nucleotides of one strand. What enzyme is used to join
the RNA nucleotides together?
15. Distinguish between introns and exons. What happens when mRNA is processed?
16. What is the function of transfer RNA? What is found at each end of the tRNA
molecule?
17. What re the 2 types of molecules in each of the 2 subunits of a ribosome? Where is
the rRNA produced? Where is the protein of the ribosomes produced? Where are the
subunits assembled and then transferred?
18. What 3 processes are required for translation? The codon that stands for the amino
acid methionine will begin the initiation of protein synthesis.
19. How many tRNA molecules will attach to a ribosome at one time?
20. The
anti-codon
of each tRNA is complementary to a particular codon in
mRNA .
21. During translation, the order of mRNA codons determines the order in which tRNA
and their attached amino acids come to a ribosome to determine the sequence of amino
acids in a polypeptide.
1
Biol 12: DNA and Protein Synthesis Review ANSWERS
A. Proteins:
1.
Enzymes
are proteins that control chemical reactions.
2. Amino acids are the monomers for a
protein
. An amino
acid consists of three groups; an amino group, an carboxyl
group and
the R group, because it is the Remainder of the molecule. Amino acids differ from one
another by their
R
group.
3. A bond that joins two amino acids is called a
peptide bond .
A
polypeptide
is a single chain of amino acids.
4. The
primary
structure is the linear sequence of the amino acids joined
by peptide bonds. The
secondary
structure of a protein comes about
when the polypeptide takes on a particular orientation in space. The
tertiary
structure of a polypeptide is its final three-dimensional shape. Separate polypeptides are
arranged to give some proteins a fourth level of structure, termed the
quaternary
structure, such as hemoglobin.
5. When proteins are exposed to extremes in heat and pH, they undergo an irreversible
change in shape called
denaturation
.
6. The peptide bond is a type of reaction called
dehydration
synthesis
where a water molecule is removed
when 2
monomers (in this case, they are
amino
acids
) are
“spliced” together. The reverse reaction is called
hydrolysis
. In this
reaction, a water molecule is
added
to break the bond between two
monomers.
7. Utilize the following terms to label the diagram below: condensation(or dehydration
synthesis),hydrolysis, H2O, disaccharide, and monosaccharide.
8. Match the following answers for proteins to one of the statements below.
a. enzymes
b. R Group
c. polypeptide
d. amino acids
e. secondary structure
f. tertiary structure
f.
protein’s final three-dimensional shape
b.
accounts for differences in amino acids
c.
a single chain of amino acids
2
Biol 12: DNA and Protein Synthesis Review ANSWERS
e.
alpha helix of a polypeptide strand
d.
monomer subunits of a protein
a.
proteins that speed up chemical reactions
Completion and Short Answer Questions.
1. All nucleotides are made up of three parts: a base, a sugar and a
group .
phosphate
2. In DNA, the base adenine, symbolized by A, is always paired with a base symbolized
by the letter
T
.
3. DNA is a
double stranded helix with the nucleotides found on the
2 sides
.
4. In RNA, the base thymine, symbolized by the letter T, is replaced by base symbolized
by a U
.
5. DNA replication is called
semi-conservative
because each new double
helix is made up of an old strand and a new strand.
6. A mutation is a change in the sequence of nucleotides within a DNA
molecule.
7. During transcription, DNA serves as a
8. A
acid.
codon (or triplet)
9. Each tRNA has a(n)
at the other end.
template
for mRNA formation.
consists of three adjacent bases that code for one amino
anticodon at one end and a specific
10. The nucleus of a cell contains coded information.
a. the name of the nucleic acid that contains this code is
amino acid
DNA
b. the nucleolus has a concentration of a nucleic acid called
RNA
11. RNA is a polynucleotide. How is its structure different from that of DNA?
a.
ribose instead of deoxyribose
b.
single stranded instead of double stranded
c.
uracil instead of Thymine
3
Biol 12: DNA and Protein Synthesis Review ANSWERS
12. The diagram below is a portion of a DNA molecule that is untwisted. Label each of
the following parts.
a. phosphate
b. deoxyribose
c. thymine (nitrogenous
base)(pyrimidine)
d. hydrogen bonds
e. adenine (purine)
f. 3’ end of sugar
g. cytosine (pyrimidine)
h. guanine (purine)
13. In the above diagram, the combination of parts a, b and c is called a
nucleotide
.
14. Regarding the above diagram, answer the following questions:
a. Which letters represent the sugar-phosphate backbone?
A&B
b. Which 2 letters represent pyrimidines?
T&C
Purines?
A&G
c. The number of purines will always
equal the number of pyrimidines.
15. When DNA is ready to divide or replicate itself, the hydrogen bonds are broken, and
the 2 strands come apart as if they were unzipped. Then there are 2 separate strands
that may look like the diagram below. Assume that replication has occurred, and
complete this diagram by drawing in complementary strands.

a. In your drawing on the last page,
each G should attach itself to (1) C
each A should attach itself to (2)
T
each C should attach itself to (3) G
each T should attach itself to (4) A
4
Biol 12: DNA and Protein Synthesis Review ANSWERS
b. Assume that the completed diagram above represents a duplicated chromosome and
that division is about to occur. Replication assures that each daughter cell will receive
an exact copy of the original DNA molecule. One of the strands will be a parental
strand; one a daughter strand. (=semi-conservative replication”)
16. Transcription
a. In the nucleus, DNA serves as a template for the production of messenger RNA
(mRNA). Let us assume that strand L in the preceding diagram will serve as the
template. What will be the message that mRNA brings to the ribosomes?
GGU GUA AUU
b. Whereas DNA has a triplet code (that is, every three nucleotides
for an amino acid
), mRNA contains
codons (triplets)
stand
, which are
complementary to the code.
17. Translation
a. In the cytoplasm there are at least twenty RNA molecules called transfer RNA (tRNA).
At one end, these have a(n) anticodon
have one of the 20
amino acids
, and at the other end they
.
b. What is the role of tRNA? To “translate” the mRNA; they transport the correct
amino acid to the ribosome and donate it to the growing a.a. chain forming.
c. Assume the mRNA molecule in question 16a above has arrived at the ribosomes.
What are the anticodons for each of the tRNA molecules in the diagram below, in
sequence?
CCA CAU UAA
d. By using “the code” in your textbook, fill in the three amino acids, in sequence, that
will be coded for by the mRNA shown below.
5
Biol 12: DNA and Protein Synthesis Review ANSWERS
18. Summary.
DNA contains a(n) (a) “blueprint”
for protein synthesis; it is a(n)
(b)
triplet code because three bases indicate one particular
(c)
amino acid
. During transcription, (d)
having bases that are (e)
complementary to the bases in DNA. Thus it is said that
DNA serves an a(n) (f) template
called (g) codons
messenger (m) RNA is produced,
for mRNA production. The bases in mRNA are
. mRNA moves into the cytoplasm and becomes associated with
the (h) ribosomes , which contain (i)ribosomal (r) RNA molecules. Also in the
cytoplasm there are (j)
transfer (t) RNA molecules with a(n) (k)
anticodon at
one end and one of the 20 amino acids at the other. During translation the tRNA
molecules bring amino acids to the ribosomes in the order dictated by the DNA code;
thus the original sequence of bases in DNA orders the (l) sequence of amino acids in a
protein.
19. Complete this table to indicate the different types of mutations.
Type of Mutation
a.
chromosomal
Definition
Change in regard to entire chromosomes
b. gene mutation
Change in regard to a single gene
c. somatic
Change that affects the body cells
d. germinal
Change that affects the gametes
6
Biol 12: DNA and Protein Synthesis Review ANSWERS
7
20. A substance that causes a mutation is called a mutagen ; if it is a substance that
causes cancer, it is called a carcinogen
.
21. There are 2 broad categories of mutagens:
chemical and
radiation.
Some examples of these mutagens are:
chemical: additives, drugs, cleaning
solutions, pesticides, PCB’s, CFC’s, etc.
Radiation: ultra violote, gamma rays, shortwave radiation, microwaves, etc
22. Germinal mutations are not often detected until
the offspring exhibit the
mutation.
23. The somatic mutation that we are most familiar with causes
Cancer
.
24. A mutation can cause a change in the primary structure of a protein, which can
ultimately affect the
secondary, tertiary¸ and quartenary structures of the protein as
well. A change in the structure of a protein will often also change the
function of
the protein as well.
25. A nonsense mutation occurs when a triplet which normally codes for an amino acid
is changed to a stop codon.
26. There are three types of gene mutations:
27. Recombinant DNA is
addition, deletion, substitution
DNA from 2 or more organisms that has been
“spliced” together.
28. Three uses for recombinant DNA are:
protein products (hormones, proteins, vaccines)
Gene Therapy
Diagnostic tests
29. During recombinant DNA experiments, a
plasmid (a small satellite piece of
bacterial DNA) is often employed. Special enzymes called restriction
enzymes are
used to cut both the bacterial and the foreign DNA. When these enzymes cut the DNA
they leave uneven ends called “sticky” ends When you mix the cut foreign DNA with
the cut bacterial DNA, they will naturally
re-anneal
, reforming the a circular
piece of DNA.
The engineered plasmid can then be
transformed (transferred)
original bacterial host to be replicated.
30. Label the following diagram of a Recombinant DNA experiment:
back into the
Biol 12: DNA and Protein Synthesis Review ANSWERS
1T
4T
R
6T
A
E
N
M
S
7P
O
L
2M
A
N
S
C
R
3A
I
P
T
I
O
N
5D
E
N
A
8
N
T
T
U
R
E
I
C
Y
M
E
10
A
S
E
O
R
E
A
I
8M
D
R
T
B
U
O
A
I
O
9T
T
O
S
A
U
N
E
15L I
G
R
N
A
A
S
E14
Biol 12: DNA and Protein Synthesis Review ANSWERS
R
11r
E
R
12C O
D
O
E
N
N
Z
N
13D E
H
Y
D
R
A
9
Y
T
I
O
N
M
E
Across:
4: DNA codes for RNA
5: an irreversible change in the protein structure
7: Enzyme that synthesizes new nucleic acids from templates
9: Carries amino acid to ribosomes
12: “triplet” of bases in mRNA
13: Name of type of reaction that converts monomers into a polymer
15: Name of enzyme that completes DNA replication on the lagging strand
Down:
1. Process used to make protein from RNA
2. Type of RNA whose sequence of codons specifies sequence of aminon acids
during protein synthesis
3. “triplet” of tRNA bases that pairs with mRNA codon
6: Will increase rate of reaction if increased.
8: agent that brings about mutations
10:Name of sugar in RNA
11. type of RNA found in Ribosomes
14. biological catalyst