26 Jun What aspect of biological information processing DOES NOT
Question
1. 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, protein.
B. It allows cells to avoid wasting valuable resources (substrates, reducing power and ATP)
synthesizing endproducts at times when those compounds happen to be available (free)
in the environment.
C. It allows cells to grow faster by increasing their levels of rate-limiting enzymes.
D. It minimizes the chance that an enzyme will use an inappropriate metabolite as substrate
when its own substrate is missing.
E. Three of the above are reasonable possibilities.
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15. You have a sequenced protein and are trying to identify its gene in a genome sequence.
The protein includes the following sequence of amino acids —
——- His(H), Try(W), Met(M), Gly (Y) ——–
How many different DNA base sequences could encode this part of the protein?
A. one
B. two
C. four
D. eight
E. 20300
16. In the problem above, imagine that you’re working on an organism with 80% G/C pairs. In this
organism, which of the base sequences (below) is most likely to encode these 4 amino acids?
A. CAU, UGG, AUG, GGA
B. CAC, UGG, AUG, CCG
C. CGG, CCG, AUG, GGG
D. CAC, CGG, CUG, GGA
E. CAC, UGG, AUG, GGU
17. You heard several examples of gene regulatory mechanisms in which a protein bound near the
promotor of a gene either facilitates or prevents transcription. If a mechanism existed to
control translation, where do you think the controlling protein would be likely to bind.
A. The mRNA-STOP region of DNA
B. The translation stop codons in the mRNA
C. In the coding region of an mRNA
D. It would bind near the initiation codon, preventing interaction with a ribosome
E. It would vary the level of some tRNA or the enzyme that attaches an amino acid to it.
18. It was suggested in lecture that the %GC pairs in any genome is established when the
mutational rates of converting A/T to G/ C (and the reverse rate) come to steady state.
If this is true, what do you think would happen when a piece of DNA from an 80% GC
organism is horizontally transferred into the chromosome of a host cell with a 20% GC
content?
A. The transferred fragment would have a higher mutation rate than other portions
of host chromosome (bp substitutions/replication)
B. The transferred fragment would have a lower mutation rate in the new host than
it had in the old host (bp substitutions/replication)
C. The transferred fragment would be treated just like all other portions of the host
chromosome and would show the same mutation rate.
D. The transferred fragment would not be replicated due to unusual base composition.
E. The mutation rate will be high if scored as base changes per replication, but low if
scored by amino acid substitution mutations per replication.
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19. Define the difference between DNA damage and mutation by choosing THE TWO INCORRECT
STATEMENTS from the list below.
A. Damage and mutation are not distinguishable
B. DNA with a mutation has no structural abnormality (obeys the Watson-Crick model).
C. DNA that is damaged disobeys Watson-Crick structure (has breaks, mispaired bases, etc)
D. One is a chemical description; the other is a biological description of the same thing.
E. Cellular mechanisms (repair enzymes) can identify abnormalities in DNA structure – they
can’t detect mutations.
20. Natural selection is one of the forces that causes allele frequencies to change from
one generation to the next. Which is its biggest affect of selection on allele frequency?
A. To increase the frequency of beneficial mutations
B. To cause the differences between amino acid sequences in orthologous genes.
C. To reduce the frequency (or remove from the population), mutations that impair
reproductive success.
D. To prevent overpopulation of the planet
E. To help life adapt to new changes in its environment.
21. New mutations arising in genome can be classified as Beneficial (good), Deleterious (bad)
or Neutral (no effect on reproductive ability). Rank these three (B, D, N) in order of the
frequency at which you expect them to appear as new mutations (most common to least common).
A. B, D, N
B. D, N, B
C. B, N, D
D. N, D, B
E. N, B, D
22. The earth-shattering impact of the Watson-Crick structure for DNA was due to —
A. Suggesting how the DNA molecule could be replicated.
B. Suggesting how base sequence could encode protein structure.
C. Demonstrating that a molecule could carry information.
D. Explaining how natural selection could work.
E. Explaining why the frequency of G and C are equal in DNA.
23. A population consisting of 10,000 individual diploid organisms is surveyed for the frequency of
its alleles of GeneA. The a1 allele is present only in individuals that have a different allele as
their second copy. Two hundred individuals had a1 as one of their alleles of GeneA. All of the
other alleles of GeneA in the population are a2, a3, a4 and a5, present in various combinations.
What is the allele frequency of a1 in this population?
A. You can’t tell without knowing about the various genotype frequencies.
B. It’s 200/10,000 or 0.02
C. It’s 200/20,000 or 0.01
D. It’s 20%, since there are four other alleles in the population; a total of 5.
E. It’s 50% — the fraction of the a1 allele among all GeneA alleles in the
genotypes that include a1.
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24. Prior to the Watson-Crick structure, which of the following was NOT used an argument in favor
of protein (rather than DNA) as genetic material?
A. Proteins had been shown to do a wide variety of amazing things.
B. DNA had never been shown to do anything biological.
C. There were more symbols (gew-gaws) in proteins than in DNA.
D. Proteins were found in the nucleus with DNA.
E. Proteins are more nutritious.
25. Which of the following possibilities best describes recombination? (Pick the most fundamental,
not necessarily the only true answer)
A. Broken ends of a piece of DNA are joined.
B. It’s how sexually reproducing organisms make offspring.
C. Two genomes interact to make new combinations of their informational differences.
D. Mutations are generated in DNA.
E. Mutations are removed from DNA.
26. In what sense does DNA have “redundant information content”?
A. Many organisms are diploid and have two copies of each gene.
B. There are two strands each of which has two doses of information.
C. There are two strands, each of which is sufficient to determine the base sequence of the
other.
D. Mutations in one copy have no effect on the other.
E. Damage to one strand leads to damage of the other.
27. Although the information content of DNA is redundant, only one of the two strands carries
information that can be expressed. Which of the following is the best explanation?
A. Transcription starting at one end of the gene can only copy one strand.
B. mRNA molecules made from opposite strands have the same sequence, but one has it
running backwards (3’-5’) which can’t be translated.
C. mRNA molecules made from opposite strands have different sequences (reading 5’-3’) and
only one of them can make sense when translated into amino acid sequence (5’-3’).
D. Only one end of the message can be used to start protein synthesis.
E. The second strand can only be copied during replication.
28. The “RNA world” was suggested as a possible precursor to modern life, which relies on the
central dogma (DNA RNA protein) — a very complex process. What aspect of the
“RNA world theory” is most attractive to those looking for a primitive life form?
A. It avoids proteins and thus doesn’t require synthesis of amino acids.
B. It avoids DNA which is extremely expensive to synthesize.
C. It allows one molecule (RNA) to serve both as the hereditary material and as a catalyst.
D. By avoiding DNA and Proteins, this form of life might better fit into small primitive
cells.
E. With RNA as a genetic material mutation rates would be higher and help evolution
move faster.
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29. Which TWO of the following are arguments against the RNA world as the initial form of life?
A. Primitive earth experiments didn’t yield much ribose or many nucleic acid bases.
B. RNA is energetically difficult to polymerize (2 high-energy phosphates per base) making
it hard to imagine that huge pools of potential polymers could have accumulated.
C. Modern RNA replication has a very high mutation rate.
D. If an RNA world were first, there should still be some of these RNA-organisms left.
E. An RNA world would not require cell membranes.
30. What’s a “gene pool”?
A. The solution of nucleoside triphosphates that get polymerized during replication.
B. A collection of free genes thought to have existed before they were collected into
chromosomes.
C. The total number of alleles of all genes that make up the genomes of the members of a
population.
D. The list of genotypes of all the individuals in a population.
E. A device to help cleanse or purify the population by removing unfavorable mutations.
31. Beyond encoding amino acid sequences, DNA includes several signals that punctuate the process
of protein production. These signals are essential to the expression of all genes. Which TWO of
the following are examples of these code punctuation marks?
A. Promoters, message terminators
B. Comma bases between codons, spaces between genes, exclamation codons to
increase gene expression.
C. Sites at which regulatory proteins bind to enhance or restrict promoter function.
D. Sites at which chromosome replication is initiated and terminated
E. Start codons, nonsense codons
32. When orthologous proteins from distantly related species are compared, amino acids at some positions
appear constant and are present in all species while amino acids at other positions differ
between species. Why are some positions invariant (unchanging)?
A. These are positions in the gene at which polymerase seldom makes a mistake.
B. These are amino acids that are unimportant and thus are seldom changed in response to the
selective pressures that favor alteration of amino acids.
C. Amino acids at these positions are essential to function of the protein.
D. These are positions at which the amino acid has many codons and the mutations occur but
result in no change in the amino acid.
E. The processes that repair mismatches act better on these sites and reduce the mutation rate.
33. To determine the biological and biochemical role of a particular gene most securely requires
forging a link (making a correlation) between the gene and what TWO things? (CHOOSE TWO!)
A. The phenotype caused by loss or alternation of the gene
B. The chromosomal region near the gene.
C. The ancestral gene from which this one is derived
D. The biochemical function of the protein encoded by the gene.
E. The frequency of mutations in the gene.
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34. Some wise person once said, “Natural selection ensures (guarantees) that a new beneficial alleles
will eventually take over (sweep = become fixed) in the population and a new deleterious (bad)
mutation will be removed” Chose the best comment, based on recent lectures.
A. This is true.
B. This is true for drift but not for natural selection
C. This is more nearly true for large populations than for small ones
D. This is only true for haploid populations.
E. This is true, but new mutations are always occurring and take some time to
be either fixed or eliminated.
35. A mutation arises that is perfectly neutral – neither beneficial nor deleterious.
What will happen to the frequency of this allele if the population is grown with a population size
maintained at 100 cells? …….at 10,000 cells? Pick the best answer.
A. It will never sweep either population
B. It will sweep both populations if the experiment is continued long enough.
C. For both populations, it will either sweep or be completely eliminated given enough time.
D. Answer “c” is right but the final outcome will take longer for the larger population.
E. It will be eliminated from the smaller population and will sweep the larger population.
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