6.4: DNA Replication

Question 1

semiconservative replication

Answer 1

mechanism of DNA replication in which each of the 2 strands of parent DNA is incorporated into a new double stranded DNA molecule

Question 2

Meselson and Stahl experiment

Answer 2

• used isotopes of nitrogen (heavy nitrogen and light nitrogen) to label parent DNA strands before replication
• after first replication single band of DNA had equal parts heavy and light nitrogen
• after 2 rounds 2 bands detected, one had density of hybrid, another had density of light nitrogen

Question 3

Replication Process

Answer 3

step 1: strand separation
step 2: complementary strands
step 3: Dealing with errors during DNA replication

Question 4

replication origin

Answer 4

specific sequence of DNA that acts as starting point for replication

Question 5

helicase

Answer 5

replication enzyme that separates and unwinds DNA strands by breaking hydrogen bonds

Question 6

replication fork

Answer 6

point of separation of 2 parent strands by breaking hydrogen bonds, forming y shaped structure

Question 7

topoisomerase

Answer 7

enzyme that relieves tension by unwinding of parent DNA by cutting 1 or 2 strands
- allow strands to untwist and rejoin the strand
- have tendency to anneal bc strands are complementary

Question 8

single strand binding protein

Answer 8

enzyme that prevents annealing of strands once separated by helicase

Question 9

replication bubble

Answer 9

space between forks, filled w newly replicated DNA

Question 10

DNA polymerases

Answer 10

enzymes that join nucleotides
- can only add nucleotides to 3’ end of existing DNA so new strand is always assembled in 5’ to 3’ direction

Question 11

nucleoside triphosphate

Answer 11

building block + energy source for replicating DNA

Question 12

RNA primase

Answer 12

replication enzyme that produces RNA primers

Question 13

RNA primer

Answer 13

replication molecule that acts as starting point for replication

Question 14

DNA polymerase III

Answer 14

prokaryotic enzyme that builds DNA strands from nucleotides

Question 15

leading strand

Answer 15

DNA strand copied in direction toward replication fork

Question 16

lagging strand

Answer 16

DNA strand copied in direction away from replication fork

Question 17

Okazaki fragments

Answer 17

piece of DNA on lagging strand

Question 18

DNA polymerase I

Answer 18

enzyme that fills in gaps in lagging strand between Okazaki fragments; proofreads final strands

Question 19

DNA ligase

Answer 19

enzyme that catalyzes formation of phosphodiester bond between 2 DNA strands and Okazaki fragments

Question 20

DNA polymerase II

Answer 20

enzyme that repairs damage to DNA, including damage that occurs between replication events