Topic 3-1

Question 1

all DNA replication needs to be:

Answer 1

accurate and fast!

Question 2

what were the three proposed models of DNA replication?

Answer 2

• conservative replication
• dispersive replication
• semiconservative replication

Question 3

Meselson and Stahl’s experiment found that the true model for DNA replication is:

Answer 3

semi-conservative

Question 4

what was Meselson and Stahl’s experiment?

Answer 4

• E.coli were grown in an 15N media first, and then were transferred to a 14N media and were allowed to replicate
• DNA from the 15N media appeared as a single, blue band; DNA from the first 14N generation were a single, purple band; DNA from the second 14N generation had a purple band and a red band

Question 5

what are the four major steps of DNA replication (in prokaryotes)?

Answer 5

1) initiation
2) unwinding
3) elongation
4) termination

Question 6

do prokaryotes have circular or linear DNA?

Answer 6

mostly circular

Question 7

describe the initiation step of DNA replication (prok)

Answer 7

the origin of replication (OriC) is recognized by the initiator complex, which causes a slight unwinding of the DNA

Question 8

what is the OriC?

Answer 8

a specific sequence of DNA that is recognized by the initiatior complex in DNA replication

Question 9

needs single stranded DNA to do its job (needs the initiator complex to open a bubble)

Answer 9

DNA helicase

Question 10

• prevents damage to ssDNA
• prevents secondary DNA structures
• sequence independent
  these are characteristics of:

Answer 10

single stranded binding proteins (SSBs)

Question 11

relieves torsion by cutting dsDNA during the unwinding phase of replication

Answer 11

DNA gyrase

Question 12

DNA polymerase can only attach nucleotides to:

Answer 12

a pre-existing 3’OH group

Question 13

DNA synthesis occurs in what direction?

Answer 13

5’ –> 3’

Question 14

How does DNA polymerase start DNA synthesis?

Answer 14

it can’t, a primase is needed

Question 15

what is the function of a primase?

Answer 15

it adds RNA primers (10-12 nucleotides long) to the ssDNA and leaves a 3’OH open for DNA polymerase to attach to

Question 16

• large muliportein complex
• synthesizes DNA strand in 5’ to 3’ direction
• has 3’ to 5’ exonuclease activity to correct errors
• high processivity
  these are all traits of:

Answer 16

DNA polymerase III

Question 17

• large multiprotein complex
• synthesizes DNA in 5’ to 3’ direction
• removes RNA primers and replaces them with nucleotides
• low processivity
  these are all traits of:

Answer 17

DNA polymerase I

Question 18

what is the function of DNA ligase?

Answer 18

joins the okazaki fragments together to make a continuous strand of DNA

Question 19

in prokaryotes, DNA replication ends when:

Answer 19

the two replication forks meet

Question 20

some organisms contain a specific _________ that stops DNA replication

Answer 20

termination sequence

Question 21

what is the alleged function of topoisomerase in theta replication?

Answer 21

they temporarily cleave the DNA

Question 22

what are the two main types of circular DNA replication?

Answer 22

theta replication and rolling-circle replication

Question 23

the base pair error rate is _______ mistakes/ 1 billion base paris

Answer 23

<1

Question 24

how is the accuracy of DNA replication acheived?

Answer 24

1) errors in base pair selection by DNA polymerase = 1/100,000
2) proofreading by DNA polymerase
3) mismatch repai occurs soon after DNA replication