3. DNA Replication

Question 0

why does our body limit the amount of proteins we make?

Answer 0

limit amount of mutations

Question 1

DNA replication error rate

Answer 1

1 in a million

Question 2

Meselson-Stahl Experiment

Answer 2

proved DNA is semiconservative
DNA replication in heavy nitrogen, centrifuge, 1 band
DNA replication light nitrogen, centrifuge, 1 band (15N, 14N)
DNA replication light nitrogen, centrifuge, 2 bands (14N both and 14/15)

Question 3

DNA replication begins at an _____ and occurs __________

Answer 3

origin; bidirectionally

Question 4

direction of synthesis

Answer 4

DNA ALWAYS synthesized 5’ to 3’

DNA template is read 3’ to 5’

Question 5

leading v. lagging strand

Answer 5

synthesis occurs continuously for leading strand

discontinuously for lagging strand (via Okazaki fragments), spliced together by DNA ligase

Question 6

DNA pol

Answer 6

catalyzes nucleophilic attack (elongation of DNA strand)

Question 7

purpose of Mg2+ ions?

Answer 7

stabilizes Asp residues on DNA pol

Question 8

DNA pol requires?

Answer 8

template & primer

responsible for elongating DNA chain and fixing errors while replicating
RNA pol does not require a primer

Question 9

2 ways to correct mistakes in DNA replication:

Answer 9

1. during replication

2. after replication

Question 10

3’ to 5’ exonuclease activity of DNA pol

Answer 10

slides back and excise the mismatch at the exonuclease site, then continues with DNA synthesis

Question 11

DNA replication mistake (tautomer)

Answer 11

tautomer form cytosine (looks like thymine)

binds active site of adenine instead of thymine, then converted back to normal cytosine

Question 12

all 3 DNA polymerases & _________ has ___________

Answer 12

have 3’ to 5’ exonuclease activity

DNA pol I has 5’ to 3’ exonuclease activity as well

Question 13

DNA replication rate

Answer 13

can’t make DNA pol move faster, can try to initiate more DNA polymerases to act

Question 14

3 steps of DNA replication

Answer 14

initiation, elongation, termination

Question 15

initiation

Answer 15

BTHPT

1. binds: DNAa binds R&I sequence
2. torque: induces torque, springs A-T rich DUE
3. helicase: binds, opens DNA sequence
4. polymerase: binds DNA strands
5. topoisomerase: relives torque from helicase activity

Question 16

elongation

Answer 16

leading strand is read 5’ to 3’
synthesized continuously

lagging strand read 5’ to 3’
synthesized discontinuously via okazaki fragments

Question 17

lagging strand elongation

Answer 17

primase adds RNA primer at replication fork, allows DNA pol to synthesize the strand by extending from the primer

Question 18

single stranded binding proteins

Answer 18

protects the single-strands of DNA

Question 19

elongation steps

Answer 19

1. continuous synthesis of leading strand proceeds as DNA is unwound by the DnaB helicase
2. clamp loader bound to ATP & B clamp
3. B clamp is loaded around the new template primer
4. ATP is hydrolyzed and B clamp closes around the DNA & dissociates from the clamp loader
5. DNA pol adds nucleotides until it hits the pervious primer
6. previous RNA primer is removed by 5’ to 3’ exonuclease activity of DNA pol I
7. fragments joined by ligase

Question 20

termination

Answer 20

Ter sequences bound by Tus enzymes signals DNA pol to terminate

topoisomerase breaks both DNA strands

Question 21

minichromosome maintenance protein (MCM)

Answer 21

helicase that creates the origin recognition complex (ORC), once ORC is formed, cell cycle is approved to divide

Question 22

replication requires what?

Answer 22

synthesis & activity of S-phase cyclin & CDK complexes

Question 23

telomeres

Answer 23

created by telomerase

RNA serves as template