lecture 4: DNA replication

Question 1

is DNA replication conservative or semiconservative

Answer 1

semiconservative

Question 2

semiconservative replication

Answer 2

each replicated DNA molecule consists of one “old” and one “new” strand

Question 3

replication starts at

Answer 3

specific sites called replication origins
* requires a short primer to add nucleotides

Question 4

the replication process:

Answer 4

• bidirectional - 2 replication forks
• chemistry of reaction demands addition of nucleotides to the 3’ end of molecules

Question 5

replication ends at

Answer 5

termination site (TER)

Question 6

DNA polymerase I function

Answer 6

directs DNA synthesis:
* requires DNA template and 4 deoxyribonucleoside triphosphates (dNTPs)
* DNA revision
* join together Okazaki fragments

Question 7

topoisomerase

Answer 7

relieves the strain caused by tight twisting ahead of the replication fork by breaking, swiveling, and rejoining DNA strands

Question 8

helicase

Answer 8

enzyme that untwists the double helix at the replication forks

Question 9

primase

Answer 9

synthesizes RNA primer as starting template

Question 10

single-strand binding proteins

Answer 10

bind to and stabilize single-stranded DNA

Question 11

DNA polymerase I, II,III all can

Answer 11

elongate existing DNA strand (primer)

Question 12

DNA polymerase I, II, III cannot

Answer 12

initiate DNA synthesis

Question 13

DNA polymerase I,II,III possess 3’ to 5’ exonuclease acitivty:

Answer 13

proofread newly synthesized DNA, remove/replace incorrect nucleotides

Question 14

only DNA polymerase I has `

Answer 14

5’-3’ exonuclease activity

Question 15

unwinding of DNA helix

Answer 15

• multiple DnaA proteins bind to ORI –> causes conformation change
• DnaB/C helicases bind and further open helix
• single stranded binding proteins (SSBP) bind and stabilize open conformation

Question 16

DNA gyrase

Answer 16

relieves coiled tension from unwinding of helix

Question 17

primase (RNA polymerase)

Answer 17

recruited to replication fork by helicase
* synthesizes a short RNA primer, which provides the free 3’ -OH required by DNA pol III for elongation

Question 18

continuous DNA synthesis:

Answer 18

leading strand

Question 19

discontinuous DNA synthesis

Answer 19

lagging strand

Question 20

DNA polymerase 3’-5’ exonuclease activity allows for

Answer 20

excision of incorrect nucleotides

Question 21

pre-replication complex (pre-RC)

Answer 21

• assembles at replication ORIs
• early G1 phase of cell cycle

Question 22

nucleosome must be __ ___ before polymerase can begin synthesis

Answer 22

stripped away

Question 23

telomeres

Answer 23

• protect intact eukaryotic chromosomes from degradation

Question 24

_’ strand on telomeres is the G-rich strand

Answer 24

3

Question 25

t-loops

Answer 25

at end of telomeres
formed by: G-rich 3’ strand (interact upstream)

Question 26

shelterin complex

Answer 26

forms around t-loops, ends are protected from nuclease digestion

Question 27

telomerase RNA component (TERC)

Answer 27

serves as guide and template for synthesis of DNA complement

Question 28

telomerase reverse transcriptase (TERT)

Answer 28

activity produces new DNA using TERC RNA template