UNIVERSITY OF THE FREE STATE
MAIN CAMPUS
GENE2626
DEPARTMENT: GENETICS
Semester test 1
ASSESSOR(S): 1. Dr M Gryzenhout
MODERATOR(S): 1. Mrs L Wessels
TIME: 60 min
MARKS: 50
Instructions
 Read questions carefully.
 All answers must be written in pen except for marking on the optical
sheet.
 Number all your answers correctly.
Question 1 [14]
1. Which of the following enzyme/proteins have this function during replication: Binds to
the Ori.
*a. Initiator protein
b. Helicase
c. Single-strand binding proteins (SSBPs)
d. Primase
e. DNA polymerase III
2. Which of the following enzyme/proteins have this function during replication: Replaces
the RNA primer with DNA.
a. Initiator protein
b. Helicase
c. Single-strand binding proteins (SSBPs)
d. Primase
e. DNA polymerase III
*f. DNA polymerase I
3. Which of the following enzymes/proteins have this function during error repair of DNA:
Cuts DNA backbone at an apurinic site.
a. DNA glycosylase
*b. AP endonuclease
c. DNA exonuclease
d. DNA endonuclease
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e. Topoisomerase
4. Match the critical enzyme to the process: Methyl directed mismatch repair.
a. Sloppy DNA polymerase
b. UvrA-UvrB complex
c. PKcs
*d. Adenine methylase
e. RNA polymerase
f. DNA glycosylase
5. Which of the following sequence motifs have this function during transcription: Signal
for ribonuclease.
a. Promoter
b. Terminator
c. Enhancer
*d. AAUAA on mRNA transcript
e. Splice donors and acceptors
6. Which of the following is typical to prokaryotes:
a. Promoter
b. Enhancer
*c. fMet
d. UTR’s
e. Start codon
f. Stop codon
7. Why were only male flies exposed to X-rays in the X-ray mutagen experiment?
a. Male flies have a Y chromosome that is unique
b. Females were difficult to work with
*c. Male flies have only 1 X chromosome that can be tracked by mating with
females
d. Only exposed males will immediately show effects to the X rays.
e. Male flies have only 1 Y chromosome that can be tracked by mating with females
8. Match the following mutation to a definition: Antimorphic allele.
*a. Prevents normal protein function
b. Gene product has weak, but detectable, activity
c. Phenotype varies continuously with the amount of functional gene product
d. Phenotype is sensitive to gene dosage (i.e. 50% of gene product)
e. Generate more gene product or the same amount of a more efficient gene
product
f. Generate gene product with new function or that is expressed at inappropriate
time or place
9. Which of the following is an example of posttranslational processing using enzymes?
*a. Zymogen
b. Glycosylation
c. Lipidation
d. Ubiquitination
e. Phosphorylation
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10. Which do not form part of a prokaryotic ribosome?
*a. 5S rRNA
b. 23S rRNA
c. 5.8S rRNA
d. 16S rRNA
11. Which of the following sequences of DNA dictates where translation will start?
a. Activator
b. DNMT
c. Poly-A signal
d. Stop codon
*e. Start codon
12. Which of the following proteins also contain RNA?
*a. Spliceosome
b. DNA ligase
c. RNA polymerase
d. Nucleosome
e. β chain of hemoglobin
13. Choose the best answer: Which of the following components of the Ames test is used
to ensure that a modified version of the tested compound could be carcinogenic?
a. Plates with histidine
b. Plates without histidine
c. Test compound
*d. Rat liver enzymes
e. Bacteria
14. Which structure fits best with the following enzyme: RPA proteins.
*a. Displacement loop
b. 3’ single stranded tails
c. Holliday junction
d. Invaded strand
e. Heteroduplex
Question 2 [10]
Indicate if the following statements are true or false and MOTIVATE your answer
2.1 The 3’ end of mRNA corresponds with the N terminus of the resulting polypeptide
chain. (2)
False, 5’ of mRNA or C of polypeptide
2.2 In the experiments of Avery to determine which compound is the transforming
principle, cells were not transformed when the RNA was degraded. (2)
False, only when DNA was degraded
2.3 A nucleoside consist of phosphor, a ribose sugar and nitrogenous base. (2)
False, that is a nucleotide/only consist of ribose and N base
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2.4 The protein dosage of a heterozygote (A+/a1) will be enough to produce wild type
eye color if A+ is the wild type allele, and a1 is a null allele. (2)
True, dosage by the one wild type allele is enough even though the null allele gives
nothing
2.5 Eukaryotes have multiple ribosome binding sites (RBSs). (2)
False, only a single binding site
Question 3 [10]
Give one outcome of the following experiments or events. Read the questions
carefully
3.1 The branch migration step of the cross-over pathway during molecular DNA
recombination. (1)
Heteroduplex enlarges
3.2 Band position in the Meselson-Stahl experiment (bottom and/or middle and/or
top) after the second replication event, that tested which DNA replication model was the
correct one, if the dispersive model turned out to be correct. (1)
Middle only
3.3 Viability of second generation Drosophila male flies in the control experiment testing
whether X-rays can be a mutagen. (1)
All would still live
3.4 Viability of second generation Drosophila male flies in the X-ray experiment testing
whether X-rays can be a mutagen. (1)
Some will die
3.5 If Leu and its correct corresponding mini-mRNA is added during the mini-mRNA
experiment. (1)
Radioactivity would be in ribosomes on filter
3.6 Addition of proflavin to bacteriophages. (1)
Deletions of insertions
3.7 Base excision repair in a DNA string. (1)
Cuts out an uracil base and replace with correct DNA
3.8 When the tRNA charged with methionine is docked in the P site of the ribosome (1).
The next charged tRNA moves into the A site based on the codon position.
3.9 When the sigma (σ) factor is released from the RNA polymerase during transcription
(1).
RNA polymerase can move along mRNA
3.10 The length of the DNA strand during trinucleotide repeat contraction of triplet
repeats in the DNA strand during replication.
Shorter/fewer repeats
Question 4 [16]
Answer the following short questions.
4.1 Give two differences (4x0.5=2) and one similarity (1) between DNA replication
and RNA transcription. (Total=3)
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Any two differences: DNA polymerase (0.5) vs RNA polymerase(0.5); makes 2 new DNA
strands (0.5) vs makes 1 RNA strand(0.5); DNA has T (0.5) RNA had U(0.5)...
Any two similarities: Both makes new nucleic acid strands(1); both have 5’-3’
direction(1); DNA double helix has to unwind in both cases (1); both have initiation and
elongation stages (1)....
4.2.1 Give any two regions in DNA that are not in exons where mutations can still disrupt
gene expression. (2)
4.2.2 Why will mutations in these regions disrupt gene expression? (1)
Interferes with binding of enzymes or ribosomes/interferes processes of
transcription or translation
4.3.1 Illustrate by using DNA strands that are going for two rounds of replication, how
oxidative damage of a guanine in a DNA strand can cause a T-A substitution. (6x0.5=3)
each DNA double strand is 0.5
4.3.2 Is this an example of a natural mutation or is it caused by a mutagen? (1)
Natural
4.4 Why is the one gene-one enzyme hypothesis technically not correct? (1)
A multimeric enzyme with different subunits requires more than one gene
4.5 Name any two events or processes that made it possible to do the mini-mRNA
experiment to determine the codon sequences for amino acids. (2)
Discovery of mRNA
Synthetic mRNA
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Cellular extracts in test tubes
4.6.1 Pose the two hypotheses for the Hershey-Chase Waring blender experiment that
used radioactivity and bacteriophages. (2x0.5=1)
DNA is the transforming principle/makes up genes (0.5)
Protein is the transforming principle/makes up genes (0.5)
4.6.2 What were the results and which hypothesis was proven? (2x0.5=1)
DNA-inked radioactivity was in the bacteria (0.5), therefore DNA is principle (0.5)
4.6.3 What would the control experiments of these be? (1)
No radioactivity
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