DNA replication in eukaryotes

Question 1

what is origin firing?

Answer 1

the transition from dsDNA to ssDNA using 3’-5’ unwinding from helicase

Question 2

eukaryote helicase

Answer 2

heterohexameric that travels 3’-5’–> composed of 6 subunits (2-7 mini chromosome maintenance factors); helicase is assembled into a “twelve-mer” which encircles dsDNA; one of the hexamers doesn’t line up exactly with the other, so when dsDNA is being fed through, it’s twisted and kinked which may initially form the replication bubble; forces dsDNA to undergo LH rotation which will break one of the based

Question 3

eukaryotic pols

Answer 3

contain pol alpha, delta, and epsilon

Question 4

role of alpha pol

Answer 4

takes the role of primase–synths a 6-10 nt segment; transitions to a 20 nt DNA extension; no proofreading activity

Question 5

role of epsilon pol

Answer 5

synthesizes on the leading strand; has 5’3–> pol activity; 3’-5’ exo activity

Question 6

role of the delta pol

Answer 6

synthesizes on the lagging strand; has 5’3–> pol activity; 3’-5’ exo activity; okazaki fragments are 200 nt rather than 2000 nt

Question 7

sliding clamp in euks

Answer 7

proliferating cell nuclear antigen; is a trimer; can encircle ssDNA but NOT dsDNA

Question 8

lagging strand clean up

Answer 8

pol delta and epsilon have strand displacement activity; flap endonuclease 1 (FEN1) will cleave the displaced ssDNA; DNA ligase I will seal the nicked DNA