Topoisomerases

Question 1

DNA supercoiling

Answer 1

occurs in all chromosomes in all cells (pro & euk); relaxed B-DNA (right handed) has 1 complete turn every 10.5 bases; structural strain by DNA underwinding is accomodated by supercoiling or strand separation

Question 2

DNA underwinding

Answer 2

can remove 1 turn (1 turn for every 12 bases - not stable/strained); molecule has fewer turns that expected of B-DNA; promotes compaction and facilitates strand separation

Question 3

Topoisomerases

Answer 3

Regulate DNA supercoiling in pro & euk cells by increasing or decreasing DNA underwinding by breaking one or both strand, changing # turns and religating strands

Question 4

Topoisomerase I

Answer 4

break 1 DNA strand, change turns by 1, religate; relaxes negative supercoils

Question 5

Topoisomerase II

Answer 5

break both DNA strands, change turns by 2, religate; introduces negative supercoils