Lecture 3: DNA repair and homologous recombination Flashcards
Which of the following best describes the function of the T-loop at the end of a chromosome?
A) It increases the rate of DNA replication.
B) It prevents the ends of chromosomes from being recognized as damaged DNA.
C) It assists in the process of chromosomal crossover during meiosis.
D) It signals for the degradation of old chromosomes.
b)
What is the primary function of telomerase in the cell?
A) To repair DNA damage caused by mutations.
B) To extend the telomeres at the ends of chromosomes.
C) To initiate the process of DNA replication.
D) To degrade damaged telomere sequences.
b)
What happens to cells with low or inactive telomerase activity?
A) They maintain their telomeres and replicate indefinitely.
B) They gradually lose telomeres, leading to aging and cell death.
C) They experience uncontrolled DNA replication.
D) They avoid DNA damage by stabilizing their chromosomes.
b)
Why are stem cells able to replicate indefinitely?
A) They have an unlimited supply of DNA polymerase.
B) They continuously extend their telomeres using telomerase.
C) They do not experience DNA replication errors.
D) They do not lose telomere sequences during DNA replication.
b)
How does the T-loop form at the end of a chromosome?
A) By the single-stranded 3’ end base pairing with a complementary sequence in another chromosome.
B) By a specialized protein inserting the single-stranded 3’ end into the duplex telomere repeats further up the chromosome.
C) By DNA polymerase folding the chromosome end into a loop.
D) By shelterin proteins binding directly to the single-stranded 3’ end.
b)
What role do shelterin proteins play at the ends of chromosomes?
A) They repair DNA strand breaks.
B) They facilitate the formation of the T-loop.
C) They attach to and protect the ends of chromosomes, distinguishing them from double-strand breaks.
D) They initiate telomerase activity for extending telomeres.
c)
Which of the following best describes the formation of thymine dimers in DNA?
A) Thymine dimers form when two thymine bases in separate DNA strands are linked together by hydrogen bonds.
B) Thymine dimers form when two adjacent thymine bases in the same DNA strand are covalently bonded due to ultraviolet (UV) radiation.
C) Thymine dimers form when two cytosine bases in different DNA molecules cross-link due to UV radiation.
D) Thymine dimers occur naturally during DNA replication without the need for UV exposure.
b)
In addition to thymine, which other pyrimidine base can form dimers upon UV exposure?
A) Adenine
B) Guanine
C) Cytosine
D) Uracil
c) Cytosine
Which of the following best describes the function of AP endonuclease and sugar phosphoesterase in base excision repair (BER)?
A) AP endonuclease removes the damaged base, while sugar phosphoesterase inserts the correct nucleotide.
B) AP endonuclease cuts the DNA backbone at an abasic site, and sugar phosphoesterase removes the deoxyribose sugar and phosphate group.
C) AP endonuclease repairs the phosphodiester bond, and sugar phosphoesterase fills in the gap with new nucleotides.
D) AP endonuclease and sugar phosphoesterase both remove the damaged base, allowing DNA polymerase to repair the DNA strand.
b)
What happens if thymine dimers are not repaired in DNA?
A) The cell becomes more resistant to UV damage
B) The cell’s genetic code becomes more accurate
C) Mutations may occur, potentially leading to cancer
D) DNA replication continues without any issues
c)
What type of damage is primarily repaired by base excision repair (BER)?
A) Large, helix-distorting lesions
B) Single-base lesions caused by oxidation, deamination, or alkylation
C) UV-induced thymine dimers
D) Double-strand breaks in the DNA
b)
Nucleotide excision repair (NER) is the primary mechanism used to repair which of the following?
A) Oxidized bases
B) Thymine dimers caused by UV radiation
C) Deaminated cytosine (uracil in DNA)
D) Single-strand breaks in DNA
b)
Which repair pathway is most responsible for fixing chemically modified individual bases, such as those damaged by oxidation or alkylation?
A) Mismatch repair (MMR)
B) Base excision repair (BER)
C) Homologous recombination (HR)
D) Nucleotide excision repair (NER)
B) BER
Which of the following statements is true about nucleotide excision repair (NER)?
A) NER repairs single-base lesions caused by chemical modifications.
B) NER removes large, bulky lesions that distort the DNA helix, such as UV-induced dimers.
C) NER is only responsible for repairing oxidative base damage.
D) NER repairs double-strand breaks in DNA.
b)
Which component of telomerase acts as a template for synthesizing new DNA telomere repeats?
A) DNA polymerase
B) RNA
C) Protein
D) Primer
b) RNA
