Exam 3 Weekly Quizzes And Questions Flashcards
The process of DNA replication requires that each of the parental DNA strands be used as a ___________________ to produce a duplicate of the opposing strand.
Template
DNA replication is considered semiconservative because ____________________________.
after many rounds of DNA replication, the original DNA double helix is still intact
each daughter DNA molecule consists of two new strands copied from the parent DNA molecule
each daughter DNA molecule consists of one strand from the parent DNA molecule and one new strand
C
If the genome of the bacterium E. coli requires about 20 minutes to replicate itself, how can the genome of the fruit fly Drosophila be replicated in only 3 minutes?
A. The Drosophila genome is smaller than the E. coli genome.
B. Eucaryotic DNA polymerase synthesizes DNA at a much faster rate than procaryotic DNA polymerase.
C. The nuclear membrane keeps the Drosophila DNA concentrated in one place in the cell, which increases the rate of polymerization.
D. Drosophila DNA contains more origins of replication than E. coli DNA.
D
Which of the following statements about the newly synthesized strand of a human chromosome is true?
A. It was synthesized from a single origin solely by continuous DNA synthesis.
B. It was synthesized from a single origin by a mixture of continuous and discontinuous DNA synthesis.
C. It was synthesized from multiple origins solely by discontinuous DNA synthesis.
D. It was synthesized from multiple origins by a mixture of continuous and discontinuous DNA synthesis.
D
You have discovered an “Exo–” mutant form of DNA polymerase in which the 3′-to-5′ exonuclease function has been destroyed but the ability to join nucleotides together is unchanged. Which of the following properties do you expect the mutant polymerase to have?
A. It will polymerize in both the 5′-to-3′ direction and the 3′-to-5′ direction.
B. It will polymerize more slowly than the normal Exo+ polymerase.
C. It will fall off the template more frequently than the normal Exo+
polymerase.
D. It will be more likely to generate mismatched base pairs.
D
DNA polymerases are processive, which means that they remain tightly associated with the template strand while moving rapidly and adding nucleotides to the growing daughter strand. Which piece of the replication machinery accounts for this characteristic?
Sliding clamp
Telomeres serve as caps at the ends of linear chromosomes. Which of the following is not true regarding the replication of telomeric sequences?
The lagging strand telomeres are not completely replicated by DNA polymerase.
Telomeres are made of repeating sequences.
Additional repeated sequences are added to the template strand.
The leading strand doubles back on itself to form a primer for the lagging strand.
D
Even though DNA polymerase has a proofreading function, it still introduces errors in the newly synthesized strand at a rate of 1 per 107 nucleotides. To what degree does the mismatch repair system decrease the error rate arising from DNA replication?
100 fold
Beside the distortion in the DNA backbone caused by a mismatched base pair, what additional mark is there on eukaryotic DNA to indicate which strand needs to be repaired?
a nick in the template strand
a chemical modification of the new strand
a nick in the new strand
a sequence gap in the new strand
A nick in new strand
The repair of mismatched base pairs or damaged nucleotides in a DNA strand requires a multistep process. Which choice below describes the known sequence of events in this process?
DNA damage is recognized, the newly synthesized strand is identified by an existing nick in the backbone, a segment of the new strand is removed by repair proteins, the gap is filled by DNA polymerase, and the strand is sealed by DNA ligase.
DNA repair polymerase simultaneously removes bases ahead of it and polymerizes the correct sequence behind it as it moves along the template. DNA ligase seals the nicks in the repaired strand.
DNA damage is recognized, the newly synthesized strand is identified by an existing nick in the backbone, a segment of the new strand is removed by an exonuclease, and the gap is repaired by DNA ligase.
A nick in the DNA is recognized, DNA repair proteins switch out the wrong base and insert the correct base, and DNA ligase seals the nick.
A
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 TCAT 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?
TTAT
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 TCAT 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?
TCT
Which of the following statements is not an accurate statement about thymidine dimers?
Thymidine dimers can cause the DNA replication machinery to stall.
Thymidine dimers are covalent links between thymidines on opposite DNA strands.
Prolonged exposure to sunlight causes thymidine dimers to form.
Repair proteins recognize thymidine dimers as a distortion in the DNA backbone.
B
Which of the following statements regarding DNA damage is true?
Ionizing radiation and oxidative damage can cause DNA double-strand breaks.
After damaged DNA has been repaired, nicks in the phosphate backbone are maintained as a way to identify the strand that was repaired.
Depurination of DNA is a rare event that is caused by ultraviolet irradiation.
Nonhomologous end joining is a mechanism that ensures that DNA double-strand breaks are repaired with a high degree of fidelity to the original DNA sequence.
A
Homologous recombination is an important mechanism in which organisms use a “back-up” copy of the DNA as a template to fix double-strand breaks without loss of genetic information. Which of the following is not necessary for homologous recombination to occur?
3′ DNA strand overhangs
5′ DNA strand overhangs
a long stretch of sequence similarity
nucleases
5′ DNA strand overhangs
