BIOL 3301
Genetics
EXAM 3
Extra exam
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Name:
SSN:
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True-false statements (write True or False in front of the statement)
(2 points each).
1. The experiments by Griffith on Streptococcus pneumoniae were the first demonstration
of bacterial transformation.
2. In a DNA molecule, nucleotides on complementary strands are held together by
covalent bonds.
3. oriC is an enzyme involved in DNA replication.
4. Telomerase is a reverse transcriptase that maintains chromosome ends.
5. The mutation causing sickle-cell anemia leads to a single amino acid substitution in
hemoglobin.
6. E. coli K is the permissive host and E. coli B is the restrictive host for rII mutants.
7. Non-complementary rII mutants are allelic.
8. Hot spots are sites that are more mutable than others.
9. Protein synthesis is terminated by a rho-dependent mechanism.
10. IF3 stimulates binding of the 30S ribosome subunit to mRNA.
Multiple choice (circle the correct answer) (2 points each).
1. A sample of normal double-stranded DNA was found to have a guanine content of
18%. What is the expected proportion of adenine ?
a. 9%
b. 32%
c. 36%
d. 68%
e. 82%
2. The figure shown below depicts the structure of:
a. dATP
b. dCTP
c. ddATP
d. UTP
e. ddTTP
3. Hershey and Chase proved that DNA is the transforming principle. They observed that
the isotope accumulated in the bacteria was:
a. 31P
b. 35S
c. 33P
d. 15N
e. none of the above
4. DNA polymerase I has three enzymatic activities. They are:
a. telomerase, RNA polymerase, helicase
b. gyrase, 3’->5’ exonuclease, 5’->3’ polymerase
c. helicase, 3’->5’ exonuclease, 5’->3’ polymerase
d. 5’->3’ exonuclease, 5’->3’ polymerase, 3’->5’ exonuclease
e. DNA polymerase I does not have 3 enzymatic activities.
5. DNA ligase catalyzes the formation of:
a. phosphodiester bonds
b. cAMP
c. ATP
d. hydrogen bonds
e. none of the above
6. B-DNA is the most common form of DNA. The spacing between basepairs is:
a. 10 A
b. 34 A
c. 3.4 A
d. 4 A
e. none of the above
7. A tRNA with the anticodon 3´AUG 5´would carry
a. phenylalanine
b. tyrosine
c. tryptophane
d. serine
e. threonine
8. Translation initiation in E. coli is mediated by basepairing of 16S rRNA to the:
a. promoter
b. origin of replication
c. Shine-Dalgarno sequence
d. transcription start site
e. none of the above
9. The following diagram shows a fragment of transcribed DNA, and the upper strand is
the template strand:
5´ CCGTTA 3´
3´ GGCAAT 5´
The transcribed RNA can be represented by:
a. 5´ AUUGCC 3´
b. 5´ TAACGG 3´
c. 5´ AUUGCC 3´
d. 5´ UAACGG 3´
e. 5´ GGCAAU 3´
10. EF-Ts is required for:
a. loading aminoacyl-tRNA into the A-site of the ribosome
b. regenerating EF-Tu
c. translocation of the peptidylchain
d. translocation of the ribosome
e. releasing empty tRNAs from the ribosome
11. Beta galactosidase converts
a. glucose to galactose
b. galactose to lactose
c. galactose to glucose and lactose
d. lactose to galactose and glucose
e. lactose to two glucose molecules
12. RNA polymerase binds to
a. repressor gene
b. promoter
c. operator
d. permease gene
e. lactose
13. A super-repressor mutation (IS) affects the Lac operon. It results in
a. no transcription
b. inducible transcription
c. transcription but no translation
d. no translation
e. constitutive transcription
14. A partial diploid of genotype I-P+O+Z-Y+/I+P-O+Z+Y+ will show
a. inducible production of beta galactosidase
b. inducible production of beta galactosidase and permease
c. constitutive production of beta galactosidase and permease
d. inducible production of permease
e. no beta galactosidase or acetylase production at all
15. The trp operon has three levels of regulation. They are:
a. trpR, enzyme inhibition by Trp, attenuation
b. trpR, lacI, cAMP-CAP
c. RNA polymerase, cAMP-CAP, lacI
d. 30S subunit, IF3, amino-acyl tRNA
e. DNA polymerase, DNA ligase, enzyme inhibition
Fill in (2 points each).
1. Two of the bases, ……… and ………., are similar in structure and are called purines .
The other two bases, ............... and ............... are called pyrimidines.
2. Meselson and Stahl demonstrated that DNA replication is ……………………….. .
3. Yanofsky studied the trp synthetase gene and demonstrated the …………………. of
gene and protein.
4. Stop codons are not recognized by aminoacyl-tRNAs, but by ………………………….
5. The trp operon has a level of regulation called attenuation , which is only possible
because prokaryotes have .............................. translation.
Homework (10 points each).
1. We are studying some of the Neurospora mutants described by Beadle and Tatum.
These mutants (numbered 1 to 7) are all involved in the same biosynthetic pathway which
yield two different end products. The different compounds generated in the different steps
are A, B, C, D, F, G, H, I. Give the order in which the compounds are made and indicate
which enzymes (corresponding to the mutants) are involved in the different biosynthetic
steps.
Compound tested (+= growth; -+ no growth)
1
2
3
4
5
6
7
A
B
C
D
F
G
H
I
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(B) In sweet peas, the synthesis of purple anthocyanin pigment in the petals is controlled
by two genes, B and D. The pathway is
white intermediate ---------------> blue intermediate ---------------> anthocyanin (purple)
gene B
gene D
enzyme
enzyme
a. What color petals would you expect in a pure-breeding plant unable to catalyze the
first reaction ?
b. What color petals would you expect in a pure-breeding plant unable to catalyze the
second reaction ?
c. If the plants in parts a and b are crossed, what color petals will the F1 plants have ?
d. What ratio of purple:blue:white plants would you expect in the F2 ?
2. You are studying a gene in E. coli that specifies a protein. A part of its sequence is:
-Phe-Tyr-Ser-Trp-Glu-Ala-Met-ThrYou recover a series of mutants for this gene that show no enzymatic activity. By
isolating the mutant enzyme products, you find the following sequences:
Mutant 1:
-Phe-Asn-Ser-Trp-Glu-Ala-Met-Thr-
Mutant 2:
-Phe-Tyr-Ser-Trp
Mutant 3:
-Phe-His-Cys-Leu-Pro-Ala-Val-Thr-
Mutant 4:
-Phe-Tyr-Met-Leu-Gly-Ala-Met-Thr-
What is the DNA sequence that specifies this part of the protein ? What is the molecular
nature for each mutation ?
Open questions (20 points).
NOTE: If you would run out of space, you can also use the back of this page to continue
your answer.
Describe all components necessary for and explain RNA transcription (initiation,
elongation, termination) and protein translation initiation in prokaryotes.