ch 6

Question 1

who discovered that DNA was replicated semi conservatively

Answer 1

Meselson and Stahl

Question 2

label

Answer 2

red: replication forks
green: replication origin
purple: template DNA
blue: newly synthesized DNA

Question 3

what opens the DNA double helix for the start of DNA replication

Answer 3

initiator proteins

Question 4

describe image

Answer 4

multiple origins of replication are opening and meeting as they replicate

Question 5

DNA polymerase can only add nucleotides to the

Answer 5

3’ end of the strand of DNA

Question 6

how fast do DNA replication forks go in bacteria vs humans

Answer 6

bacteria: 1000 nucleotide pairs per sec
humans: 100 nucleotide pairs per sec

Question 7

what does DNA polymerase do

Answer 7

this enzyme catalyzes the addition of nucleotides to 3’ end of DNA

Question 8

what is the leading strand of DNA

Answer 8

the strand of DNA that is replicated continuously

Question 9

what is the lagging strand of DNA

Answer 9

the strand of DNA that is made discontinuously

Question 10

what are okasaki fragments

Answer 10

small DNA pieces added to the lagging strand

Question 11

what supplies the energy for a nucleotide to be added to the DNA strand

Answer 11

the incoming nucleoside triphosphate

Question 12

how many phosphates must break off the incoming nucleoside triphosphate to attach to the DNA strand

Answer 12

2

Question 13

the template strand will always be

Answer 13

3’ - 5’

Question 14

what is primase and what does it do

Answer 14

• produces an RNA “primer” that is complementary to the template DNA strand
• DNA polymerase builds onto the primer
• RNA primer is later removed and replaced with DNA

Question 15

understand

Answer 15

okay

Question 16

about how often does DNA polymerase make a mistake

Answer 16

every 10^7 nucleotide pairs it copies

Question 17

understand

Answer 17

okay

Question 18

what does DNA polymerase do to proofread

Answer 18

it checks to make sure if the right base was added before it moves on, if the wrong one was added it clips it off and tries again

Question 19

what replaces the RNA primers with DNA

Answer 19

repair polymerase

Question 20

what does DNA ligase do

Answer 20

joins the 5’ phosphate end of one DNA fragment to the adjacent 3’ hydroxyl end of the next (closes any gaps)

Question 21

why do primers made of RNA frequently contain mistakes

Answer 21

because they are made of RNA they cant proofread

Question 22

what does helicase do? what problems does it cause

Answer 22

it prys open the double helix of DNA, but the DNA ahead of the split gets wound very tightly

Question 23

what does DNA topoisomerase do

Answer 23

relieves the pressure caused by helicase by creating a transient single strand nick in the DNA backbone which temporarily releases tension. the enzyme then reseals the nick before falling off the DNA

Question 24

what does the sliding clamp protein do

Answer 24

keep DNA polymerase firmly attached to the template while it synthesizes new DNA

Question 25

understand

Answer 25

okay

Question 26

what does clamp loader protein do

Answer 26

uses energy from ATP hydrolysis to lock the sliding clamp onto DNA

Question 27

what are telomeres

Answer 27

long repetitive nucleotide sequences to the ends of every chromosome

Question 28

what do telomeres attract

Answer 28

telomerase

Question 29

what is telomerase

Answer 29

an enzyme that carries its own RNA template which it uses to add multiple copies of the same repetitive DNA sequence to the lagging strand template

Question 30

what does single strand DNA binding protein do

Answer 30

binds to single stranded DNA exposed by DNA helicase, preventing base pairs from re-forming before the lagging strand can be replicated