Module 5: DNA Replication

Question 1

Semiconservative

Answer 1

1 of 2 strands conserved in each progeny molecule

each double helix has 1 old strand and 1 new

Question 2

Conservative

Answer 2

1 of 2 daughter duplexes is conserved parental duplex, other is completely newly synthesized

Question 3

Dispersive

Answer 3

parental material is scattered through the structures of the daughter duplexes

Question 4

DNA rep

Answer 4

semiconservative

bidirectional -proceeds in both directions from the same starting point

Question 5

Leading Strand

Answer 5

5’–>3’

Question 6

Lagging strand

Answer 6

3’–>5’

Question 7

Helicase

Answer 7

separates the DNA double helix into its 2 antiparallel strands
creates bubble in DNA

Question 8

SSB pr-

Answer 8

bind to the single stranded DNA strands
coat each DNA single strand
prevent reannealing before replication can occur

Question 9

Primase

Answer 9

synthesizes a short RNA primer in the 5’–> 3’ direction

Question 10

DNA polymerase III

Answer 10

bind to the 3’end of the RNA primer and begin replicating the DNA
in a 5’–>3’ direction

Question 11

RNase H

Answer 11

recognizes the RNA nucleotides and hydrolyzes them thereby removing the RNA primer from the newly replicated daughter DNA strand

Question 12

DNA polymerase I

Answer 12

fills in the gap by replicating a DNA primer in its place

Question 13

DNA ligase

Answer 13

binds to and rejoins the covalent phosphodiester bonds between the newly replicated DNA primer and the strand

Question 14

Okazaki fragments

Answer 14

small synthesized fragments on lagging strand

covalently linked together by DNA ligase once the RNA primers have been hydrolyzed and replaced with DNA

Question 15

Active Site Constraints

Answer 15

active site of DNA polymerase I accommodates only the correct W-C base pairs
does not easily allow for incorrect base pairs to fit

Question 16

Exonuclease Activity

Answer 16

catalyses cleavage of nucleotide from end of DNA/RNA polymer
can move backward (3’->5’) to remove incorrectly matched bases

Question 17

Exonuclease repair process

Answer 17

1. Polymerase mispairs dC w dT
2. Polymerase repositions mispaired 3’ terminus into 3’–>5’ exonuclease site
3. Exonuclease hydrolyzes mispaired dC
4. 3’ terminus repositions back to polymerase site
5. Polymerase incorporates correct nucleotide, dA

Question 18

1955

Answer 18

DNA Polymerase I was isolated in E. coli extracts

Question 19

1970s

Answer 19

DNA polymerases II and III were discovered

Question 20

Late 1990s

Answer 20

DNA Pol IV and V were discovered

Question 21

E.coli DNA pol III

Answer 21

holoenzyme made up of 10 subunits

• Sits at each replication fork
• Works as a dimer, performing leading and lagging strand synthesis at the same time
• Uses an RNA primer, which is made by primase
• Has enormous processivity (enzyme’s ability to catalyze)