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Student’s Name_______________________________
Section number and TA’s name:_________________
BIOL 202
HOMEWORK #6
DUE: Mar 4/5 in your discussion section.
IMPORTANT: Please type (not hand-write) your answers onto the question sheet itself
(this sheet), then print out the final version and hand it in to your TA at the start of
Discussion section. Diagrams can be hand-drawn. Please highlight or otherwise indicate
the parts that you have typed with underlining or bolding. If additional working is
required, it will be specifically stated so in the question, and whether the working should
be shown on the answer sheet or a supplemental sheet will also be stated.
1. In the replication bubble below, label all ends of newly made DNA (in bold) with
either 5’ or 3’ (as shown in one example below): 2 pts
My drawing was getting a little crowded so I only labeled one of each fragment.
3’
3’
5’
5’
5’
3’
5’
5’
3’
5’
3’
3’
2. Answer the following questions regarding primase:
a. What type of nucleic acid is synthesized by primase? 0.5 pts
RNA
b. Why must primase create a primer for DNA synthesis? 1 pt
DNA polymerases require a polynucleotide primer with a free 3’ OH.
c. Which enzyme (in E. coli) removes the primer after synthesis is completed? 0.5 pts
DNA Polymerase I
3. Why do mutations that inactivate the 3'-5' exonuclease activity of DNA polymerase III
greatly increase the frequency of mutations? Inactivation of the 3’-5’ exonuclease
activity inactivates the proofreading capability of DNA polymerases. If proofreading
is abolished, DNA polymerase cannot fix an incorrectly incorporated nucleotide.
What would be the effect of a mutation that inactivated the 5'-3' exonuclease activity of
DNA polymerase I? 2 pts
RNA primers could not be removed by DNA polI
4. You isolated DNA from a newly discovered plant and determined that 32% of all of
the bases are adenine. What are the percentages of thymine, cytosine and guanine? 1 pt
32% Thymine; 18% Cytosine;18% Guanine
5. The synthesis of a particular essential amino acid is known to be a two-step process
that requires two different enzymes, as follows: 2 pts
Enzyme A
Precursor molecule

Enzyme B
Intermediate

Amino acid
A research laboratory has cultured strains of wild-type bacteria and two mutant strains,
one of which is deficient for enzyme A and the other for enzyme B. The tubes in which
these three types of bacteria are cultured are not labeled. In an attempt to identify them,
the three strains are grown under the following conditions:
Strain
1 (B)
2 (A)
3
Growth on minimal medium with no
supplementations
No growth (-)
No growth (-)
Growth (+)
Growth with supplementation of
intermediate
No growth (-)
Growth (+)
Growth (+)
a. Identify which strain is deficient for enzyme A, and which is deficient for enzyme B.
b. If an additional strain was deficient in both enzymes, could it be distinguished from
strain 1, using the above experimental approach?
No, it could not be distinguished from strain 1 using the approach above. If the
strain was deficient in both enzymes it could not grown on either minimal medium
or the intermediate.
6. Explain why the “one gene-one enzyme” concept is not considered completely
accurate today. 1 pt
The correct statement is “one gene-one polypeptide”. Genes do encode enzymes but
enzymes are just one class of proteins. And, really, they shouldn’t get full credit for
saying “one gene-one protein” because some proteins have quaternary structure and
require multiple polypeptides…maybe 0.75 and I’ll address it a bit in class ahead of
time.
7. In his transformation experiments, Griffith observed that
A) mutant mice were resistant to bacterial infections
B) mixing a heat –killed pathogenic strain of bacteria with a living nonpathogenic
strain can convert some of the living cells into the pathogenic form.
C) mixing a heat-killed nonpathogenic strain of bacteria with a living pathogenic
strain can convert some of the living cells into the nonpathogenic form.
D) infecting mice with nonpathogenic strains of bacteria makes them resistant to
pathogenic strains
E) mice infected
8. Chargaff’s analysis of the relative base composition of DNA was significant because
he was able to show that
A) the relative proportion of each of the four bases differs from species to species
B) the human genome is more complex that that of other species
C) the amount of A is always equivalent to T, and C to G
D) both A and C
E) A, B and C
9. The DNA double helix has a uniform diameter because _________, which have two
rings, always pair with _________, which have one ring.
A) purines; pyrimidines
B) pyrimidines; purines
C) deoxyribose sugars; ribose sugars
D) ribose sugars; deoxyribose sugars
E) nucleotides; nucleoside triphosphates
10. What did the results from the Meselson and Stahl experiment demonstrate?
The semi-conservative model for DNA replication. Each strand of the double
helix serves as a template for replication and after replication each DNA
double helix is a combination of the old strand and the new strand.