1C

Question 1

Models of DNA replication

Answer 1

1. Semi conservative (daughter + complimentary parental)
2. Conservative (daughter+daughter)
3. Dispersion (mix daughter and parent)

Question 2

Meselson and Stahl goal

Answer 2

1. Track parental and newly synthesize DNA over many generation with nitrogen isotope incorporated into DNA molecules through nitrogenous base (15N)

(Line test thing)

Question 3

Where are nucleotides added for DNA synthesis

Answer 3

At 3’-OH so DNA synthesis occurs in 5’->3’ direction…

Question 4

During DNA synthesis what provides E for the formation of new phosphodiester bonds

Answer 4

Hydrolysis of pyrophosphate

Question 5

Properties of DNA poly

Answer 5

-synthesize new DNA in 5->3
-read template DNA strand in 3->5
-CANNOT synthesize from scratch needs RNA primer + 3’-OH for synthesis
-single active site catalyze 4 diff rxns (dATP, dCTP, dGTP,dTTP)

Question 6

Replisome

Answer 6

Molecular machine of enzymes that replicates DNA

Question 7

Helicase

Answer 7

Unwinds double helix by breaking h-bons

Question 8

Primase

Answer 8

Synthesize RNA primer for DNA poly

Question 9

Single strand binding protein

Answer 9

Stabilise ssDNA before replication… how? Prevent reannealing so strand can serve as template

Question 10

DNA topoisomerase/gyrase

Answer 10

Remove super coil that form ahead of replication fork… relieve torque of mainly circular DNA

Question 11

DNA poly III

Answer 11

Synthesize DNA by adding nucleotides to new DNA strand

Question 12

DNA poly I

Answer 12

Remove RNA primer and fill gaps with DNA

Question 13

Sliding clamp

Answer 13

Attaches DNA Pol III to DNA template…replication more efficient

Question 14

DNA ligase

Answer 14

Join ends of DNA segments by forming phosphodiester bonds

Question 15

Replication forks??

Answer 15

Site of DNA synthesis

Question 16

Which strand is synthesized continuously and which is synthesized discontinuously during DNA replication

Answer 16

1. lagging is discontinuous
2. Leading is continuous (Okazaki fragments)

Question 17

DNA replication enzymes in order

Answer 17

1. DNA helicase-unwind double helix
2. RNA primase-put RNA primer
3. Topoisomerase/gyrase- prevent twisting ahead of replication fork during unwinding
   4.DNA pol. III-extend RNA primer
4. DNA helicase keepsunwinding leading and lagging strand by DNA Pol III
5. DNA Pol I-removes RNA primer of Okazaki fragments and fill gap with dNTPs (deoxynucleotide triphosphate)
6. DNA ligase-seal gap with phosphodiester bond

Question 18

DNA replication of bacterial chromosomes

Answer 18

1. Initiation: unwind and separate 2 template DNA strands at oriC (origin of replication site)
   2.elongation: synthesis of 2 new DNA strands from template strands by DNA poly (simultaneous)
2. Termination: DNA replication stop at termination site (circular) or at end of chromosome (linear)

Question 19

DNA replication of eukaryotic chromosome

Answer 19

-linear chromosome
-Multiple origin
-replication in opp. Direction (away from origin)
-end of linear chromosome has problem replicating

Question 20

PCR

Answer 20

Polymerase chain rxn (DNA replication and amplification in test tube)

Question 21

Issue replicating ends of linear chromosomes (end of replication probem)

Answer 21

-need RNA primer, why? Intimate new DNA synthesis so 3’end of linear chromosome replication is complicated
-no DNA poly can fill gap at chromosomal end=> additive loss at end
-gene at end of chromosome can be deleted….=> death of organism

Question 22

How do telomeres fix the end replication problem

Answer 22

-add noncoding ssDNA to 3’ end by telomerase
-telomeres worn away after each DNA replication/division
-if telomere region is gone=?cell stop dividing

Question 23

Telomerase?

Answer 23

Enzyme=>restore shortened teloemres

Question 24

Is telomerase in eukaryotic cells?

Answer 24

NOOO…=> short telomeres in old peep

Telomerase in gametes and stem cells (as get older, shorter telomeres cause less telomerase)

Question 25

HTERT

Answer 25

Gene mutation (human telomerase)=>biomarker in cancer

Question 26

DNA high fidelity…

Answer 26

-replicated fully -no errors … if not, -> defective genome (and maybe death) So, DNA repair mechanism by enzyme complex lower replication error rate

Question 27

Telomere role in replication

Answer 27

Ensure ends of linear chromosomes are fully replicated

Question 28

Which way does DNA Pol III synthesize new strand

Answer 28

5->3

Question 29

DNA poly proofreading

Answer 29

-optimum conformation -DNA pol III see mistake and uses 3->5 exonuclease to remove mismatched nucleotides and replace correct to contîntes synthesis in 5->3

Question 30

MMR

Answer 30

DNA mismatch repair

Question 31

Use of MMR

Answer 31

Cover replication errors not corrected by proofreading

Question 32

How does MMR work… process?

Answer 32

1. recognize mismatch damage by DNA binding protein (MutS and MutL)… 2. MutH endonuclease daughter strand away from mismatch 3. Exo1 5’-3’ exonuclease excise region of daughter strand around mismatch 4. DNA Pol III fills gap and repais mismatch 5. Gap waged by DNA ligase