DNA replication

Question 1

semi-conservative

Answer 1

after replication each double helix contains one parent strand and one new daughter strand

Question 2

bidirectional

Answer 2

replication simulataneously moves away from origin in both directions

Question 3

Okazaki fragments

Answer 3

short fragments formed on the lagging strand

Question 4

origin of replication

Answer 4

one site per chromosome in prokaryotes, and 100’s in eukaryotes

Question 5

fork

Answer 5

sites at which DNA synthesis is occuring

Question 6

origin binding protiens

Answer 6

recognize and bind to origins or replication (AT rich sequences)

Question 7

helicases

Answer 7

unwinds the helix ahead of the replication fork

Question 8

ssbp

Answer 8

after the helicase unwinds the strands, ssbp bind to each single strand to keep them separated

Question 9

primase

Answer 9

catalyzes the rxn forming the RNA to serve as a primer for the polymerases

Question 10

DNA polymerase I

in prokaryotes

Answer 10

less processivity than III. has a clean-up fxn. mediates replacement of primer with 5-3 exonuclease and 5-3 polymerase activity. proofreads 3-5

Question 11

DNA polymerase III

in prokaryotes

Answer 11

the major replicative enzyme. Higher processivity b/c it has a sliding clamp which keeps it attached to DNA over long distances

Question 12

DNA Ligase

Answer 12

binds the Okazaki Fragments/segments of lagging strand.

Question 13

Topoisomerase/gyrase

Answer 13

act to prevent extreme supercoiling of parental helix, by breaking and rejoining DNA. Gyrase- mostly foudn in prokaryotes and inhibited by quinolones.

Question 14

Telomerase/reverse transcriptase

Answer 14

Retroviruses- synthesize DNA from RNA.
Telomerase- has reverse transcriptase activity. it carries it’s own RNA template to restore telomeres in human cancer cells and stem cells. Telomoerase is supressed in normal cells.

Question 15

how polymerase creates phosphodiester bonds during addition of dNTP

Answer 15

adds dexyribonucleotides to the 3’ hydroxyls of the RNA primer, and then to the growing strand.

Question 16

DNA polymerase requires ? to start and only synthesizes in a ? direction, and it corrects replication errors by ? activity.

Answer 16

RNA primer, 5-3, 3-5 exonuclease proofreading

Question 17

Order of events

Answer 17

origin binding protiens bind, helicase unwinds, ssbp and topoisomerases maintain openness, primer binds, polymerase synthesized. okazaki fragments binded by ligase. RNA primers removed and replaced by DNA polymerase I.

Question 18

Leading strand

Answer 18

continuous copying in 3-5 direction towards replication fork

Question 19

lagging strand

Answer 19

discontinuous copying in 3-5 direction away from replication fork.

Question 20

End Replication Problem

Answer 20

Lagging stand cannot be synthesized to very end, b/c you need an RNA primer to bind upstream from each synthesized region. There is nowhere to bind to synthesize the end. So the end gets shorter and shorter until it signals cell death.

Question 21

Eukaryotes have 3 polymerases

Answer 21

Pol-a, a holoenzyme has primase and polymerase activity. It starts synthesis for about 20dNTP and then is swapped for Pol-g on lagging strand, and Pol-e on leading strand.

Question 22

Fidelity of replication is high b/c

Answer 22

polymerases discriminate based on H-bonds between base pairs, and geometry of bonds. Errors during replication are corrected by 3-5 proofreading.