Old Quiz 3 Flashcards
Which of the following is a danger of break-induced replication
- Failure to repair damaged replication forks
- Failure to repair damaged regions of direct repeats
- Failure to repair double-strand breaks during the first prophase stage of meiosis
- Failure to repair a cytosine to adenine mutation
- Failure to repair an O6-methylguanine which leads to a guanine to adenine mutation
- Failure to repair damaged replication forks
The holliday junciton is the primary DNA structure involved during homologous recombination between two sets of double-stranded DNA
True or False?
True
What reaction is catalyzed by the AlkB enzyme?
A: AlkB is a light-catalysed photolyase that excites an electron with binds to FADH and repairs pyrimidine dimers.
B: AlkB is an exonuclease that excises nucleotides on the 3’-end of a double stranded break
C: AlkB is a gyrase enzyme that overwinds DNA ahead of a broken replication fork
D: AlkB is an alpha-ketoglutarate dioxygenase that oxidizes the 1-methyl group of 1-methyladenine using O2 and an Fe2+ cofactor.
E: AlkB is a protein that binds 5’-resected ends during single-strand annealing, preventing them from annealing to the wrong strand.
D. AlkB is an alpha-ketogluterate dioxygnease that oxidizes the 1-methyl group of 1-methyladenine using O2 and an Fe2+ cofactor
T or F: Mutations in the MLH1 gene can result in faulty DNA repair in colorectal cancer
True
T or F: Homologous recombination is an appropriate genetic repair mechanism when only 1-2 nucleotides are mutated
False
Which of the following characterizes single strand annealing? (SSA)
A: Double-strand break in a direct repeat, 5’-resection, binding and resolution by replication protein A and Rad52.
B: Double-strand break in a direct repeat, 5’-resection, binding by Spo11 and second end capture, ligation, and resolution.
C: Double-strand break anywhere in chromosome, 5’-resection, binding by MSH2/MSH3/MSH6/MLH1 and resolution.
D: Double-strand break in replication fork, 5’-resection, invasion of a similar sequence on homologous chromosome, resolution.
E: Single-strand annealing is carried out by DNA polymerase during DNA replication.
A: Double-strand break in a direct repeat, 5’-resection, binding and resolution by replication protein A and Rad52.
Which of the following homologous recombination mechanisms has the greatest degree of fidelity with respect to the repaired region?
A: Synthesis-dependent strand annealing
B: Double-strand break repair during meiosis
C: Break induced replication
D: Single-strand annealing
E: Strand invasion from a chromosome with 50% sequence homology to the damaged region
A: Synthesis-dependent strand annealing
Which of the following examples describes site-specific recombination?
A: During the first meiotic prophase, sister chromatids form Holliday junctions in which material is swapped to enhance genetic fitness.
B: A plasmid contains the conserved attB site which recombines with a similar site in the chromosome of a bacterium via an integrase enzyme.
C: A region of chromosome 3 undergoes a double stranded break. Spo11 generates 3’-resected ends, which undergo strand invasion, and are repaired via DNA polymerase.
D: A region of chromosome 18 undergoes a double-stranded break and is duplicated during the next round of DNA replication.
E: MSH2/MSH3/MSH6 recognize a mutation and recruit MLH1. Together, these loop the DNA, excise the mutated material, and DNA polymerase
B: A plasmid contains the conserved attB site which recombines with a similar site in the chromosome of a bacterium via an integrase enzyme
Which of the following mechanisms is used to repair DNA alkylation damage?
A: Double stranded break repair B: Base excision repair C: Nucleotide excision repair D: Direct repair E: Mismatch repair
D: Direct repair
What is the purpose of direct repair?
A: It is used primarily to fix cytosine deamination to uracil
B: It is used primarily to fix mismatched basepairs (i.e. when thymine is incorporated instead of adenine)
C: It is used primarily to fix replication slippage errors
D: It involves excision of small regions of DNA (26-29mer fragments) with pyrimidine dimers and subsequent filling in of DNA by DNA polymerase epsilon.
E: It is used to repair UV-induced pyrimidine dimers via DNA photolyases that use a free radical mechanism to reverse the damage without excising the nucleotides.
E: It is used to repair UV-induced pyrimidine dimers via DNA photolyases that use a free radical mechanism to reverse the damage without excising the nucleotides.
Which of the following is NOT a step in long patch base excision repair?
A: A glycosylase recognizes a specific base mismatch and hydrolyzes the N-glycosidic bond of the base pair ✗ B: AP endonuclease nicks the strand 5’ to the mismatch
C: DNA polymerase delta and epsilon catalyze DNA fill in the missing base pairs
D: Lyase catalyzes intramolecular attack of the sugar ring, forcing it to open
E: Ligase-1 seals the nick in the phosphodiester backbone
D: Lyase catalyzes intramolecular attack of the sugar ring, forcing it to open
DNA polymerase sometimes undergoes replication slippage. This is a phenomenon in which DNA polymerase accidentally incorporates extra nucleotides, creating an erroneous dinucleotide or trinucleotide expansion and mismatched basepairs. Which of the following is the MAJOR route for repairing mismatched base pairs?
A: MSH2/MSH3/MSH6 hydrolyze ATP to nick one strand of DNA, MLH1 is recruited, the DNA is looped. Exonucleases and DNA polymerase ε degrade old genetic material and fill in new base pairs.
B: Glycosylases hydrolyze an N-glycosidic bond, resulting in an abasic site. AP endonuclease I nicks the 5’-end and DNA polymerase delta and epsilon replace the nucleic acid material.
C: An excinuclease hydrolyzes the sixth bond on the 3’-end of the mutation and the twenty-second bond 5’ to the mutation. The 27 -29mer fragment is removed and DNA polymerase epsilon fills in the gap and DNA ligase seals the nick.
D: MTHFpolyGlu is activated in 400 nm light, which excites an electron to bind to FADH, which then donates an electron to fix the mutation directly.
E: Spo11 generates a free 3’-end on the mutated strand of DNA, which invades an unmutated strand on another chromosome. DNA polymerase synthesizes new material and removes old material with a 5’–>3’ exonuclease function.
A: MSH2/MSH3/MSH6 hydrolyze ATP to nick one strand of DNA, MLH1 is recruited, the DNA is looped. Exonucleases and DNA polymerase ε degrade old genetic material and fill in new base pairs.
Cytosine can be spontaneously deaminated to form uracil. Which of the following methods describes base excision repair?
A: MSH2/MSH3/MSH6 hydrolyze ATP to nick one strand of DNA, MLH1 is recruited, the DNA is looped. Exonucleases and DNA polymerase ε degrade old genetic material and fill in new base pairs.
B: Glycosylases hydrolyze an N-glycosidic bond, resulting in an abasic site. AP endonuclease I nicks the 5’-end and DNA polymerase delta and epsilon replace the nucleic acid material.
C: An excinuclease hydrolyzes the sixth bond on the 3’-end of the mutation and the twenty-second bond 5’ to the mutation. The 27-29mer fragment is removed and DNA polymerase epsilon fills in the gap and DNA ligase seals the nick.
D: MTHFpolyGlu is activated in 400 nm light, which excites an electron to bind to FADH, which then donates an electron to fix the mutation directly.
E: Spo11 generates a free 3’-end on the mutated strand of DNA, which invades an unmutated strand on another chromosome.
B: Glycosylases hydrolyze an N-glycosidic bond, resulting in an abasic site. AP endonuclease I nicks the 5’-end and DNA polymerase delta and epsilon replace the nucleic acid material.
John is a 58-year-old male with early stage colorectal adenocarcinoma. He is currently prescribed 5-fluorouracil for treatment, pending the results of pharmacogenetic testing for mutations in the dihydropyrimidine dehydrogenase gene. Which of the following outcomes would describe a frameshift mutation?
A: The gene has a UAA (leucine) mutation to UAG (leucine) mutation.
B: The gene features removal of two codons.
C: The gene features insertion of a single cytosine into the middle of a codon.
D: The gene has undergone 1905+1G>A that causes intron 3 not to be processed correctly.
E: The gene undergoes homologous recombination with an unrelated sequence in chromosome 11, resulting in translocation of the intact gene.
C: The gene features insertion of a single cytosine into the middle of a codon.
Which of the following is the LEAST common mutation?
A: Chromosomal insertion B: Missense mutation C: Frameshift mutation D: Splicing mutation E: Deletion
A: Chromosomal insertion
D: Splicing mutation
