Genetics Exam 3 - practice questions and repair mechanism chart

pyrimidine dimers; other specific types of alterations

direct

double-strand breaks (2 terms)

homology directed repair and non homologous end joining (NHEJ)

replication errors, including mispaired bases and strand slippage

mismatch

DNA damage that distorts the double helix, including abnormal bases, modified bases, and pyrimidine dimers

nucleotide excision

Sometimes, chemical damage to DNA can occur just before DNA replication begins, not giving the repair system enough time to correct the error before the DNA is duplicated. This gives rise to mutation. If the cytosine in the sequence 5' TCAT 3' is deaminated and not repaired, which of the following is the point mutation you would observe after this segment has undergone two rounds of DNA replication? A. 5' TTAT 3' B. 5' TUAT 3' C. 5' TGAT 3' D. 5' TAAT 3'

A

The epsilon (ε) subunit of DNA polymerase III of E. coli has exonuclease activity. How does it function in the proofreading process? The epsilon subunit ________. A) removes a mismatched nucleotide B) excises a segment of DNA around the mismatched base C) can recognize which strand is the template or parent strand and which is the new strand of DNA. D) adds nucleotide triphosphates to the 3' end of the growing DNA strand

A

The spontaneous loss of amino groups from adenine in DNA results in hypoxanthine, an uncommon base, opposite thymine. What combination of proteins could repair such damage? A. nuclease, DNA polymerase, DNA ligase B. telomerase, primase, DNA polymerase C. telomerase, helicase, single-strand binding protein D. DNA ligase, replication fork proteins, nuclease

A

which of these proteins' primary function is to stabilize single stranded DNA A) single-stranded binding protein B) Helicase C) DNA polymerase III D) RNA primase E) DNA ligase

A

A researcher wants to treat C. elegans with a mutagen that will result in base damage (thereby interrupting and "blocking" DNA synthesis). Which of these mutagens should he use to achieve this goal? A. an intercalating agent B. ultraviolet light C. ethylmethanesulfonate (EMS) D. a base analog E. 2-aminopurine (2-AP)

B

A student is studying different types of point mutations within rabbits. Normally, a specific stretch of rabbit DNA has the sequence 5'-TGAGTCTGAAGTCC-3'. However, the student has identified the following point mutation in the same stretch of DNA: 5'-TGAGTCC*GAAGTCC-3'. This is an example of a(n) a - transversion. b - transition. c - insertion. d - deletion. e - frameshift mutation

B

Mismatch mistakes can result in all of the following except for A. Nonsense mutation B. Insertion C. Missense mutation D. Silence mutation

B

Which of the following statements is not an accurate statement about thymine dimers? A. Thymine dimers can cause the DNA replication machinery to stall. B. Thymine dimers are covalent links between thymines on opposite DNA strands. C. Prolonged exposure to sunlight causes thymine dimers to form. D. Repair proteins recognize thymine dimers as a distortion (mistakes) in the DNA.

B

Which of these proteins' primary function is unwinding the double-stranded DNA at the replication fork? A) single-stranded binding protein B) Helicase C) DNA polymerase III D) RNA primase E) DNA ligase

B

Which pattern in the figure would you expect if the DNA was replicated in a conservative manner? A) A B) B C) C D) D

B

Which spontaneous mutation mechanism leads to trinucleotide-repeat diseases in humans such as fragile X syndrome? A. nitrous acids B. replication slippage C. ionizing radiation D. wobble base pairing E. deamination

B

A point mutation in a gene of interest has resulted in the following codon change in the mRNA product of this gene: UGU ® UGA (where UGA is a stop codon, and UGU encodes the amino acid cysteine). This is an example of a a - conservative substitution b - missense mutation c - synonymous mutation d - nonsense mutation e - frameshift mutation.

D

A space probe returns with a culture of a microorganism found on a distant planet. Analysis shows that there is a carbon-based life-form that has DNA. Further analysis shows the organism's DNA only contains "heavy" nitrogen (15N). The scientist transfer the microorganism to 14N medium. After 1 generation of DNA replication, which pattern in the figure would you expect if the DNA was replicated in a semi-conservative manner? A) A B) B C) C D) D

D

In humans, xeroderma pigmentosum (XP) is a disorder of the nucleotide excision repair mechanism. These individuals are unable to repair DNA damage caused by ultraviolet light. Which of the following are the most prominent types of DNA alternation in individuals suffering from xeroderma pigmentosum? A. mismatch errors B. telomere shortening C. methylation of purines D. thymine dimers

D

which of the statements is shared feature of DNA replication in both prokaryotic (ex: bacteria) and higher eukaryotes (ex: humans) A) DNA replication is semiconservative B) multiple replication origins will be found on each replicating chromosome C) replication will proceed "bidirectionally" from an origin of replication D) the same proteins are used in both E) A and B F) A and C G) A and D H) B and C

F

True or False and correct if false: The exonuclease activity of DNA polymerase III cleaves DNA in the 5′-to-3′ direction.

False - 3'-to-5' exonuclease activity

True or False: Defect in DNA polymerase III would cause the accumulation of Okazaki fragments in the lagging strand

False - DNA polymerase I

True or False: Nonhomologous end joining is a mechanism that ensures that DNA double-strand breaks are repaired with a high degree of fidelity (accurately) to the original DNA sequence.

False - NHEJ is error prone

True or False and correct if false: Nonsense mutation tends to cause gain-of-function at the protein level.

False - cause loss-of-function; rarely gain-of-function

True or False and correct if false: In bacterial cells, mismatch repair proteins recognize the replication mistakes on the newly synthesized strand because it is methylated.

False - newly synthesized strand is unmethylated

True or False and correct if false: telomere and telomerase can be found in both animal and bacterial cells.

False - only found in animals

Which of the following changes in the open reading frame is most likely to result in a loss of function? A. a base-pair deletion B. an addition of three nucleotides C. an addition of two nucleotides D. a codon deletion E. A and B F. B and D G. A and C

G

abnormal bases, modified bases, and pyrimidine dimers

base excision

A pregnant mouse is exposed to high levels of a mutagen. Many of the mice in her litter are deformed, but when they are interbred with each other, all their offspring are normal. Which of the following statements could explain these results? A. In the deformed mice, somatic cells but not germ cells were mutated. B. The original mouse's germ cells were mutated. C. In the deformed mice, germ cells but not somatic cells were mutated. D. The mutation in the new born are repaired.

A

A student is studying different types of point mutations within rabbits. Normally, a specific stretch of rabbit DNA has the sequence 5'-TGAGTCTGAAGTCC-3'. However, the student has identified the following point mutation in the same stretch of DNA: 5'-TGAGTCG*GAAGTCC-3'. This is an example of a(n) a - transversion. b - transition. c - insertion. d - deletion. e - frameshift mutation.

A

Lysine and arginine are two amino acids with similar R groups and similar biochemical behavior. A point mutation results in the substitution of lysine for arginine and has no detectable effect on the function of that protein. This is an example of a A. synonymous mutation. B. frameshift mutation. C. conservative substitution. D. nonconservative substitution. E. Nonsynonymous mutation

C

Replication slippage on the DNA template strand during DNA synthesis can lead to which of the following mutation if it is not being fixed by DNA repair system A. Mismatch B. Insertion C. Deletion D. Base substitution E. Synonymous mutation

C

Researchers found a strain of bacteria that had mutation rates one hundred times higher than normal. Which of the following statements correctly describes the most likely cause of these results? A. The single-strand binding proteins were malfunctioning during DNA replication. B. There were one or more base pair mismatches in the RNA primer. C. The proofreading mechanism of DNA polymerase was not working properly. D. The DNA polymerase was unable to add bases to the growing nucleic acid chain.

C

Several members of the same family were diagnosed with the same kind of cancer when they were unusually young. Which one of the following is the most likely explanation for this phenomenon? It is possible that the individuals with the cancer have _______________________. A. inherited a cancer-causing gene that suffered a mutation in an ancestor's somatic cells. B. inherited a mutation in a gene required for DNA synthesis. C. inherited a mutation in a gene required for mismatch repair. D. inherited a mutation in a gene required for the synthesis of purine nucleotides.

C

Sometimes, chemical damage to DNA can occur just before DNA replication begins, not giving the repair system enough time to correct the error before the DNA is duplicated. This gives rise to mutation. If the adenosine in the sequence 5'TCAT 3' is depurinated and not repaired, which of the following is the point mutation you would observe after this segment has undergone two rounds of DNA replication? A. TCGT B. TAT C. TCT D. TGTT

C

Which of the following is most likely to result from reduced or very little active telomerase activity? A. Cells may become cancerous. B. Telomere lengthens in germ cells. C. Cells age and begin to lose function. D. Cells maintain normal functioning.

C

Which of the following statements describes the effect of a nonsense mutation on a gene? A. It changes only one amino acid in the encoded protein. B. It has no effect on the amino acid sequence of the encoded protein. C. It introduces a premature stop codon into the mRNA. D. It alters the reading frame of the mRNA.

C

True or False and correct if false: The severity of the disease caused by the expanding nucleotide mutation depends on the number of trinucleotide repeats.

True

True or False: Gyrase (Topoisomerase) can break phosphodiester bond

True

True or False: In cells, primers are synthesized by a type of RNA polymerase

True