DNA Replication Lec. 3

Question 1

Initiation

Answer 1

replication bubble at ORI
ori- origin of replication and usually high amounts of A and T

Question 2

ORC

Answer 2

Original recognition complex
attaches to ori and separates strands

Question 3

Semiconservative

Answer 3

One old piece of ssDNA.
* One new piece of ssDNA

Question 4

Helicase

Answer 4

breaks H-bonds to unzip dsDNA

Question 5

Topoisomerase

Answer 5

Relaxes supercoiling of dsDNA because it often gets +supercoiled ahead of rep. fork

Question 6

Primase

Answer 6

makes short RNA primer needed to initiate DNA synthesis

Question 7

Ligase

Answer 7

joins ribose-phosphate backbones where two new strands meet

Question 8

SSB

Answer 8

stabilizes ssDNA and prevents reannealing

Question 9

DNA Poly

Answer 9

prokaryotes have dozens eukaryotes have about 12
replicates by extension but cannot start its own new strand
also proofreads

Question 10

dsDNA antiparallel

Answer 10

polym travels 3 to 5 and synthesizes from 5 to 3

Question 11

Okazaki fragments

Answer 11

Bound by ligase to form strand dna poly can’t bind
lagging strand

Question 12

Terminus Problem

Answer 12

with every replication a 3 prime overhang forms where primer is degraded because poly cant fill in gaps in lagging strand
(more is removed every rep)

Question 13

Telomeres

Answer 13

1000s of nucleotides capping chromosome ends.
* Non-coding: not part of any genes required to “do” something.
- can act as a primer for DNA synthesis
-caps prevent massive chrom. forming together

Question 14

processivity

Answer 14

number of nucleotides that can be synthesized

Question 15

FIdelity

Answer 15

how few mistakes are made during synthesis

Question 16

Replisome

Answer 16

DNA polymerases on leading and lagging strands form pol dimer at fork.
* Joined by catalytic cores.
* Increase speed.
* Less likely to disassociate.
Accessory protein: β-clamp.
* Ring of proteins helps DNA pol slide along ssDNA

Question 17

Redundant repair mechanisms

Answer 17

-Base-excision repair (BER).
- Post-replication mismatch repair (MMR).
- Nucleotide-excision repair (NER)

BER chemically altered bases.
* MMR for mismatches.
* NER for bulky lesions.

Question 18

exonuclease

Answer 18

Mismatched bases “felt” by DNA pol.
* Lesion in backbone causes pol shape
change.
* Pushes exonuclease subunit of pol
into contact with nucleotide
leads to removal

Question 19

Base excision Repair

Answer 19

-Most important after proofreading
DNS glyco-sylases cleave base-sugar bond
AP endonuclease makes cutout
dRpase removes stretch of DNA
polymerase snyth. new DNA
Ligase seals nicks

Question 20

Mismatch Repair

Answer 20

Recognizes mismatched nucleotides
after replication.
* MutS protein “feels” and binds to
distortions in normal double helix.
* Triggers replacement of mismatched
nucleotide

Question 21

Methylated DNA

Answer 21

Methyl group added to specific carbon in purine/pyrimidine ring.

Regulates transcription of genes,turning them on/off.

Heritable: passed on through semiconservative replication.

Question 22

Nucleotide excision repair

Answer 22

damaged lesions recognized
special helicase separates on either side of lesion
strand removed and new DNA snythesized, ligase seals