DNA Replication Flashcards

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1
Q

What are the 3 potential models for DNA replication?

A

Conservative, semi-conservative, and dispersive

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2
Q

What would Messelson and Stahl have seen if DNA replication proceeded like the conservative model?

A

After the first round of replication, one band for the heavy isotope at the bottom and one band for the light isotope at the top. After the second round, same thing

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3
Q

What would Messelson and Stahl have seen if DNA replication proceeded like the semi-conservative model?

A

After the first round of replication, one band in the middle that is a hybrid of light and heavy isotopes. After the second round, would have the hybrid band in the middle and a band of the light isotope higher up

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4
Q

What would Messelson and Stahl have seen if DNA replication proceeded like the dispersive model?

A

After the first round of replication, one band in the middle that is a hybrid of light and heavy isotopes. After the second round, would still have one band of the hybrid, but would be higher up as more light isotope got incorporated in

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5
Q

What is the origin of replication? How many are there?

A

Is an AT rich region where the strands separate and replication begins. One in bacteria, many in eukaryotes

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6
Q

Which direction does replication proceed in?

A

Bidirectional from Ori

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7
Q

What is the difference between the leading and lagging strands?

A

Leading strand has 3’ end exposed, and the new strand runs 5’ to 3’. Lagging strand has the 5’ end exposed and the new strand is made of discontinuous Okazaki fragments

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8
Q

Why is there a leading strand and lagging strand?

A

DNA polymerase can only add nucleotides in the 5’ to 3’ direction, and the lagging strand runs opposite to that

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9
Q

What are the 7 key proteins in E. coli DNA replication?

A

DNA polymerase 3, DNA polymerase 1, primase, helicase, topoisomerase, SSBs, DNA ligase

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10
Q

What is the function of DNA polymerase 3?

A

Does most of the DNA synthesis and also does some proofreading

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11
Q

What is the function of DNA polymerase 1?

A

Removes primers and fills in those gaps with DNA and proofreading

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12
Q

What is the function of primase?

A

Make RNA primers needed to start synthesis

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13
Q

What is the function of DNA helicase?

A

Break the hydrogen bonds via ATP hydrolysis, that keep the strands together and unwind the strands

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14
Q

What is the function of topoisomerase?

A

Relieve the tension ahead of the replication bubble, unwind supercoiled DNA

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15
Q

What is the function of SSBs?

A

Single strand binding proteins. They bind to single strand DNA and stop it from reannealing

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16
Q

What is the function of DNA ligase?

A

Connects the Okazaki fragments

17
Q

What are the steps of DNA synthesis?

A
  1. Helicase unwinds the strands, topoisomerase stays ahead of it
  2. Primase adds a short RNA primer
  3. DNA polymerase 3 synthesizes nucleotides
  4. DNA polymerase 1 removes the primers and synthesizes DNA in their place
  5. DNA ligase connects adjacent fragments
18
Q

How is replication different in eukaryotes?

A

Chromatin: histones and chromatin proteins have to be disassembled for replication then reassembled
Larger and more complex chromosomes: more proteins involved, many origins of replication
Linear chromosomes: telomeres at the ends of chromosomes

19
Q

What are telomeres? What is the enzyme involved?

A

Telomeres are specialized sequences of DNA at the ends of eukaryotic chromosomes. The gap created when DNA polymerase 1 removes the primer isn’t filled like the internal gaps. Telomerase comes in and makes more of that sequence, until there’s another Okazaki fragment