Chapter 34 - DNA Replication

Question 1

Exonucleases

Answer 1

Remove mismatches.

Question 2

Trombone Model

Answer 2

The lagging strand is looped so that it passes through the polymerase active site in the 3’ → 5’ direction, allowing synthesis to occur in the 5’ → 3’ direction. After DNA of ~1000 nucleotides in length is synthesized, the loop is released and a new loop is formed.

Question 3

Holoenzyme

Answer 3

Contains DnaB helicase ring (unwinds DNA) and 2 polymerase cores (synthesizes DNA).

Question 4

DNA Polymerase I

Answer 4

Used in replication and DNA repair. Has exonuclease activity that removes mismatched nucleotides from the 3’ end of the DNA. An incorrectly inserted nucleotide moves from the polymerase active site to the nearby exonuclease active site where it is hydrolytically cleaved.

Question 5

Telomerase

Answer 5

Contains an RNA template that is used to extend the leading strand. High telomerase activity is a characteristic of cancer cells.