DNA Replication

Question 1

What are the 3 potential models for DNA replication?

Answer 1

Conservative, semi-conservative, and dispersive

Question 2

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

Answer 2

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

Question 3

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

Answer 3

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

Question 4

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

Answer 4

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

Question 5

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

Answer 5

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

Question 6

Which direction does replication proceed in?

Answer 6

Bidirectional from Ori

Question 7

What is the difference between the leading and lagging strands?

Answer 7

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

Question 8

Why is there a leading strand and lagging strand?

Answer 8

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

Question 9

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

Answer 9

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

Question 10

What is the function of DNA polymerase 3?

Answer 10

Does most of the DNA synthesis and also does some proofreading

Question 11

What is the function of DNA polymerase 1?

Answer 11

Removes primers and fills in those gaps with DNA and proofreading

Question 12

What is the function of primase?

Answer 12

Make RNA primers needed to start synthesis

Question 13

What is the function of DNA helicase?

Answer 13

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

Question 14

What is the function of topoisomerase?

Answer 14

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

Question 15

What is the function of SSBs?

Answer 15

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

Question 16

What is the function of DNA ligase?

Answer 16

Connects the Okazaki fragments

Question 17

What are the steps of DNA synthesis?

Answer 17

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

Question 18

How is replication different in eukaryotes?

Answer 18

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

Question 19

What are telomeres? What is the enzyme involved?

Answer 19

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