Semidiscontinuous DNA replication

Question 1

single strand DNA binding proteins (SSBs) purpose

Answer 1

after the helicase unwinds the DNA, the ssDNA is prevented from reannealing by binding to SSBs (200/fork)

Question 2

DNA pol III dimer fn

Answer 2

initiatioes polymerization by add dNTP to the RNA primer on each of the strands

Question 3

why are the two strands synthesised differently

Answer 3

stands are in anitparallel configuration and DNA pol adds dNTPs in 5 to 3 direction

Question 4

leading strand features

Answer 4

synthesized continuously; only one primer required; DNA pol III moves in same direction as replication fork

Question 5

lagging strand synthesis

Answer 5

synthesized discontinuously as Okazaki fragments, which are later ligated by DNA ligase. each OF requires a primer. DNA pol moves in opposite direction to fork

Question 6

has are lagging strands synthesis

Answer 6

DNA pol III ends polymerization when it encounters dsDNA ahead (from previous OF) dissociates from DNA, leaving a gap in one strand. this gap is recognized as damaged DNA and repaired by DNA pol I

Question 7

DNA pol I fn

Answer 7

removes primers and fills in gaps (has 5 to 3 exonuclease activity

Question 8

DNA ligase

Answer 8

joins 3’ end of one OF to 5’ end of downstream OF. as helicase unwinds DNA ahead of fork, positive supercoils form elsewhere in the molecule.

Question 9

topoisomerases

Answer 9

for fork to move, helix must rotat. introduces -ive supercoil to counteract supercoils by helicases