u4: dna replication

Question 1

histone

Answer 1

• wrap around chromatin
• form nucleosome
• do gene regulation

Question 2

what part of the cell cycle is dna replication?

Answer 2

S-phase

Question 3

who came up with an approach to dna replication? waht was this approach

Answer 3

• meselson and stahl
• semi-conservative approach

Question 4

3 models for dna replication

Answer 4

• semiconservative
• conservative
• dispersive

Question 5

what did meselson and stahl propose?

Answer 5

the proposed models for dna replication could be tested if original parental strand and new daughter strand were differentiated when dna is copied

Question 6

how did meselson and stahl conduct their experiment?

Answer 6

• gen 0: grew bacteria with isotope 15N until bacterial cells had 15N in their dna
• gen 1: transferred pop’n with 15N into culture medium with 15N = dna replication
• gen 2: dna replicatoin round, same as gen 1

Question 7

why did meselson and stahl use nitrogen isotopes

Answer 7

• nitrogen is an essential component of dna
• it would be incorporated into daughter strands

Question 8

which nitrogen isotope is heavy? light?

Answer 8

• 14N is light
• 15N is heavy

Question 9

results of meselson and stahl experiment?

Answer 9

• semi-conservative
• 1/2 low density dna
• 1/2 intermediate density dna

Question 10

semiconservative replication model

Answer 10

• both dna strands separate
• each strand acts as template for new strand synthesis

Question 11

conservative replication model

Answer 11

• whole dna acts as model for daughter synthesis

Question 12

dispersive replication model

Answer 12

• dna backbone breaks every 10 nucleotides
• new dna is synthesized in short pieces of alternating strands

Question 13

helicase

Answer 13

replication enzyme: separates and unwinds dna strands

Question 14

topoisomerase

Answer 14

class of enzymes: allow dna strands to untwist and relieve tension caused by unwinding of parent dna

Question 15

polymerase I

Answer 15

prokaryotic replication enzyme: fills in gaps in lagging strands in okazaki fragments + proofreads final strands

Question 16

polymerase II

Answer 16

prokaryotic replication enzyme: repairs dna damage + damage caused during replication

Question 17

ligase

Answer 17

enzyme: catalyzes phosphodiester bond rxn btwn two DNA strands and btwn Okazaki fragments

Question 18

RNA primase

Answer 18

replication enzyme: makes RNA primers

Question 19

steps of dna replication

Answer 19

1. replication bubbles open at origin of replication
2. double helix unwound by dna helicase
3. single stranded binding proteins (ssbp) keeps helices apart
4. dna topoisomerase releases tension forces
   - then lagging/leading strand

Question 20

leading strand steps

Answer 20

1. RNA primase adds primer to beginning of strand
2. dna polymerase III adds nucleotides continuously in 5’ to 3’ direction

Question 21

lagging strand steps

Answer 21

1. RNA primase adds RNA primers
2. nucelotides added in short okazaki fragments by dna polymerase III
3. dna polymerase I replaces RNA primers w/ dna
4. dna ligase glues okazaki fragments together w/ phosphodiester bonds
5. replication in lagging strand is non-continuous

Question 22

how does DNA polymerase III look like during replication

Answer 22

• only one
• two donut shaped rings replicate both strands simultaneously

Question 23

which enzymes can proofread? which only repairs damage?

Answer 23

proofreaders: dna polymerase I, dna polymerase III
damage-fizer: dna polymerase II

Question 24

what do the polymerases do if there is a mistake?

Answer 24

act as an exonuclease

Question 25

exonuclease

Answer 25

can cut out and replace mistakes

Question 26

what are telomeres? what do they do?

Answer 26

- repeating sequences of dna at the ends of chromosomes (where rna primer used to be) - w/o telomeres, chromosomes would shorten during every dna division = lost dna

Question 27

telomerase

Answer 27

- enzyme - adds in repeat TTAGGG to dna telomere