Lecture 3 - DNA Structure and Replication 2

Question 1

What experiment did Meselson and Stahl develop?

Answer 1

They labeled cells in N15, then allowed them to grow in N14. They found that after DNA replicated, some had N14 and N15 while others had just N15.

Question 2

What are the three models for DNA replication?

Answer 2

1. Semiconservative model
2. Conservative model
3. Dispersive model

Question 3

What is the semiconservative model?

Answer 3

Two strands of the parental double helix unwinds, and each specifies a new daughter strand by base-pairing rules

Question 4

What would the semiconservative model look like in the experiment after one replication? 2?

Answer 4

0. Start with only a 15N/15N band
1. Have 14N/15N band
2. Have 14N/15N + 14N/14N band

Question 5

What is the origin of replication in E. coli?

Answer 5

oriC

Question 6

What is the replication fork?

Answer 6

Point at which DNA unwinds to allow replication

Question 7

How can DNA unwind so quickly without it becoming tangled?

Answer 7

1. Helicase disrupts hydrogen bonds holding strands together
2. Single-strand DNA-binding (SSB) proteins bind to ssDNA and stabilize
3. Topoisomerase relax supercoiled DNA by breaking either a single DNA or both strands
4. DNA rotates to remove supercoils
5. Topoisomerase rejoins the DNA strand

Question 8

What is the name of the topoisomerase involved in DNA replication?

Answer 8

DNA gyrase

Question 9

What is the DNA replication helicase made up of?

Answer 9

6 copies of DnaB

Question 10

What are the two components of the origin of replication?

Answer 10

1. DnaA boxes (13 bp sequence that is highly conserved)
2. AT-rich region (unwinds in response to DnaA binding)

Question 11

What is the replication fork?

Answer 11

A point at which DNA unwinds to allow replication

Question 12

What direction does DNA synthesis/replication occur?

Answer 12

5’ to 3’ direction

Question 13

Why is DNA replication described as semidiscontinuous?

Answer 13

because one DNA template is synthesized continuously and the other strand is synthesized as a series of discontinuous fragments

Question 14

What is the leading strand?

Answer 14

strand where you see continuous synthesis

Question 15

What is the lagging strand?

Answer 15

strand where you see discontinuous synthesis

Question 16

What are Okazaki fragments?

Answer 16

They are the short discontinuous segments of newly synthesized DNA which make up the lagging strand.

Question 17

Describe DNA replication

Answer 17

1. Primase synthesizes RNA primers
2. DNA polymerase III synthesizes DNA
3. DNA polymerase I removes the RNA primers and fills it in with DNA
4. DNA ligase catalyzes phosphodiester bond between adjacent fragments

Question 18

How is DNA replication so accurate?

Answer 18

DNA pol I and DNA pol III possess a 3’-to-5’ exonuclease activity, which serves a “proofreading” function

Question 19

How many origins of replication does bacteria have?

Answer 19

1

Question 20

How DNA replication initiated in eukaryotes?

Answer 20

1. ORC binds to binds to consensus sequence
2. ORC recruits Cdc6
3. They recruit helicase/Cdt1 complex
4. They recruit a second helicase/Cdt1 complex
5. Helicase is recruited, slides in a 5’ to 3’ direction to unzip the helix

Question 21

What are telomeres?

Answer 21

tip, or end, of a chromosome

Question 22

How do you lengthen the telomere?

Answer 22

1. Telomerase, an RNA-protein complex, extends the 3’-end DNA overhang.
2. Primase and DNA polymerases then use this overhang to fill in the end of the other DNA strand.
3. TRF1, TRF2 proteins bind to the telomeric repeats forming the telomeric cap

Question 23

Prokaryotic and eukaryotic replication is ________

Answer 23

conserved

Question 24

Know how to label 7-23 and 7-16 diagram

Answer 24

goodnotes

Question 25

What is the polymerase III holoenzyme?

Answer 25

a complex which consists of:
a) 2 pol III units
b) 2 B clamps (attachment)
c) accessory proteins