A 71-year-old man with colorectal cancer comes to the physician for follow-up examination after undergoing a sigmoid colectomy. The physician recommends adjuvant chemotherapy with an agent that results in single-stranded DNA breaks. This chemotherapeutic agent most likely has an effect on which of the following enzymes?
ADNA polymerase III
BTopoisomerase I
CHelicase
DTelomerase
ETopoisomerase II
An investigator isolates bacteria from a patient who presented with dysuria and urinary frequency. These bacteria grow rapidly in pink colonies on MacConkey agar. During replication of these bacteria, the DNA strands are unwound at the origin of replication, forming two Y-shaped replication forks that open in opposite directions. At each replication fork, daughter strands are synthesized from the template strands in a 5′ to 3′ direction. On one strand, the DNA is synthesized continuously; on the other strand, the DNA is synthesized in short segments. The investigator finds that three enzymes are directly involved in elongating the DNA of the lagging strand in these bacteria. One of these enzymes has an additional function that the others do not possess. Which of the following steps in DNA replication is unique to this enzyme?
AElongation of lagging strand in 5'→3' direction
BExcision of nucleotides with 5'→3' exonuclease activity
CPrevention of reannealing of the leading strand and the lagging strand
DCreation of ribonucleotide primers
EProofreading for mismatched nucleotides
An investigator is studying the biology of human sperm cells. She isolates spermatogonia obtained on a testicular biopsy from a group of healthy male volunteers. She finds that the DNA of spermatogonia obtained from these men show a large number of TTAGGG sequence repeats. This finding can best be explained by increased activity of an enzyme with which of the following functions?
ALigation of Okazaki fragments
BProofreading of synthesized daughter strands
CRNA-dependent synthesis of DNA
DProduction of short RNA sequences
EHemimethylation of DNA strand
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