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Flashcards in DNA replication Deck (22)
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1
Q

semi-conservative

A

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

2
Q

bidirectional

A

replication simulataneously moves away from origin in both directions

3
Q

Okazaki fragments

A

short fragments formed on the lagging strand

4
Q

origin of replication

A

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

5
Q

fork

A

sites at which DNA synthesis is occuring

6
Q

origin binding protiens

A

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

7
Q

helicases

A

unwinds the helix ahead of the replication fork

8
Q

ssbp

A

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

9
Q

primase

A

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

10
Q

DNA polymerase I

in prokaryotes

A

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

11
Q

DNA polymerase III

in prokaryotes

A

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

12
Q

DNA Ligase

A

binds the Okazaki Fragments/segments of lagging strand.

13
Q

Topoisomerase/gyrase

A

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

14
Q

Telomerase/reverse transcriptase

A

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.

15
Q

how polymerase creates phosphodiester bonds during addition of dNTP

A

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

16
Q

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

A

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

17
Q

Order of events

A

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.

18
Q

Leading strand

A

continuous copying in 3-5 direction towards replication fork

19
Q

lagging strand

A

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

20
Q

End Replication Problem

A

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.

21
Q

Eukaryotes have 3 polymerases

A

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.

22
Q

Fidelity of replication is high b/c

A

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