29 Jul WHICH OF THE FOLLOWING IS /ARE THE MOST LIKELY ADVANTAGE(S) PROVIDED BY THESE MECHANISMS?
What aspect of biological information processing DOES NOT involve adding nucleotides at the
3’ end of a growing polynucleotide chain?
A. Chromosome replication
B. transcription
C. translation
D. DNA excision repair
E. “Two-looks” editing during replication
2. Which aspects of cell biology require the ability of complementary single strands of DNA to
reanneal to form a duplex?
A. DNA replication AND excision repair
B. Editing in replication AND translation (two-looks)
C. Translation AND transcription
D. Recombination AND Making a deletion mutation
E. Formation of base substitutions AND frameshift mutations
3. At what 3-base DNA sequence could transition mutations occur that generate a UAG or a UGA
nonsense mutation, but not a UAA nonsense mutation? Write the sequence of the DNA sense
strand (resembles the mRNA) 5’ to 3’.
A. GGA
B. UGG
C. CCA
D. TGG
E . TAA
4. The bases adenine (A) and guanine (G) are purines – the other two (cytosine C and thymidine T)
are pyrimidines. Based on your knowledge DNA structure, why are transition mutations
(A/T ↔ G/C) more common than transversion mutations (all other kinds of base substitutions?)
A. A/T base pairs are more common than G/C base pairs.
B. It’s easier for repair systems to recognize mispaired bases that are purine: purine or
pyrimidine:pyrimidine pairs.
C. The enzyme responsible for replicating DNA seldom mistakes a purine for a
pyrimidine, but it more often confuses two purines or two pyrimidines.
D. There’s no firm reason; it’s just the way things are.
E. Both b and c are reasonable and likely to contribute to the high frequency of
transitions.
5. When a normal code punctuation signal (UAA, UAG or UGA) appears within a previously open
reading frame, what is the consequence for the produced protein?
A. An incorrect amino acid is inserted at that spot
B. A series of incorrect amino acids are added after the altered spot
C. The protein is stopped prematurely and a fragment is released.
D. A full-length protein is produced with one amino acid missing at the critical position
E. These punctuation marks will have no effect in the middle of a gene.
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6. Consider the codon UUG (for leucine). Changing each of the bases in this codon to “A” would
have consequences for the protein that range from dire to minimal. List the 3 positions (base 1, 2,
3) in order of the severity of the consequence for the protein (SEVERE TO MINIMAL) of the
change to A.
A. 1, 2, 3
B. 2, 3, 1
C. 2, 1, 3
D. 3, 2, 1
E. 3, 1, 2
A particular gene has tryptophan (W) (codon UGG) at one position. How many DNA sequence
changes (mutations) and what kind of mutation would be required to make the gene produce a protein
having at this position each of the following amino acids? (transition is an exchange of A/T for G/C in
either direction) (transversion is any other base substitution)
7. Cysteine (C) codon UGU to UGC
A. 1 transition
B. 1 transversion
C. 2 transitions
D. 2 transversions
E. 3 mutations (2 transitions and 1 transversion)
8. Methionine (M) codon AUG
A. 1 transition
B. 1 transversion
C. 2 transitions
D. 2 transversions
E. 3 mutations (2 transitions and 1 transversion)
9. Histidine (H) codon CAU/C
A. 1 transversion
B. 1 transiition
C. 2 transitions
D. 2 transversions
E. 3 mutations (2 transitions and 1 transversion)
10. A mutation occurs that destroys the ability of a bacterium to repress (shut off) a negatively
regulated gene (like the lactose genes). (now the gene is on all the time) Which of the following
types of mutation is most likely to be responsible? (Hint: think about target size!)
A. a null mutation in the gene for the repressor protein (no active repressor produced)
B. a change in the site (near the lactose genes) that binds the repressor
C. a change that improves the promoter
D. a change within the gene for lactose utilization
E. a change within RNA polymerase that allows it to ignore the repressor
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11. When DNA is replicated, one strand is made in a single long stretch (leading) while the other
(lagging) is made in small patches that are later linked together. When the sequence below is
replicated will the long (leading) strand use the “top” or “bottom” strand of the diagram as
template?
5’_______3’
3’_______5’
A. Top strand
B. Bottom strand
C. Both top and bottom
D. Top strand if replication is from the left
E. Top strand if replication is from the right.
12. What would you say is the best evidence that DNA encodes information that is translated (via the
genetic code) into the amino acid sequence of proteins. (This evidence wasn’t available when
DNA was first proposed to play this role)
A. Experimentally changing one base pair in a gene often but not always results in an amino acid
change in a protein.
B. Every known organism (never mind viruses) uses DNA.
C. Mutations in one gene cause a cell to lose the activity of one protein.
D. Adding copies of a particular gene to a cell causes an increase in the intra-cellular level of one
particular protein.
E. Adding a novel gene (of known base sequence) to a cell causes appearance of a novel protein
whose amino acid sequence fits (via the code) with the added base sequence.
13. If a cellular process acts correctly 80% of the time, how will its error rate be improved by adding
an editing function of the “two-looks” type — each look has the same likelihood of error?
A. All error will be eliminated.
B. The reliability will be doubled – error frequency cut in halve.
C. Since each look has the same likelihood of error, no improvement will
be provided.
D. The likelihood of getting it right will go from 80% to 64% (80% of 80%)
E. The likelihood of error will go from 20% to 4% (20% of 20%)
14. The expression of genes is often regulated. That is, more of the encoded protein is made
under some growth conditions than others. Which of the following is /are the most likely
advantage(s) provided by these mechanisms?
A. It allows cells to shut off whole pathways when they’re not needed and thus avoid the
metabolic cost of making the corresponding mRNA, prote
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