3-1

Question 1

DNA replication needs to be

Answer 1

Accurate and fast

Question 2

Complementary bases suggest that each strand of a double helix could serve as

Answer 2

A template

Question 3

Three proposed models of DNA replication

Answer 3

Conservative replication

Dispersive replication

Semiconservative replication

Question 4

Conservative replication

Answer 4

Two original strands stay together in one molecule (double helix)

Question 5

Dispersive replication

Answer 5

Each strand gets broken down, copied, and then reassembled

Question 6

Semi-conservative

Answer 6

Each strand serves as a template, is copied, and each strand stays intact but two strands do not come back together

Question 7

All DNA takes places in a

Answer 7

Semiconservative manner

Question 8

Meselson and Stahl’s experiment

Answer 8

Creates an intermediate band of DNA between N14 and N15 after one round of replication to rule out conservative replication

Creates a intermediate band and a light band after a second round of replication to rule out dispersive replication

Agrees with semi-conservative replication

Question 9

Major steps in DNA replication

Answer 9

Initiation

Unwinding

Elongation

Termination

Question 10

Initiation

Answer 10

Prokaryotes have circular DNA with an OriC

OriC is recognized by initiator proteins, slightly unwinding DNA at the Ori

Question 11

Unwinding

Answer 11

Stretch of DNA unwinds

Helicase and other single stranded binding proteins attach to single stranded DNA

Question 12

Unwinding

Dna replication requires

Answer 12

Single stranded DNA

Question 13

Unwinding

DNA Helicase needs

Answer 13

Single stranded DNA to do its job

Question 14

Unwinding

DNA helicase

Answer 14

Breaks hydrogen bonds

Question 15

Unwinding

Single stranded binding proteins

Answer 15

Protect single stranded DNA

Prevents secondary DNA structures

Sequence independent

Form tetramers

Question 16

Unwinding

DNA gyrase

Answer 16

Topoisomerase (type II)

Relieves torsion by cutting DNA (dsDNA break)

Removes a twist via ATP

Reseals broken DNA ends

Question 17

Elongation

DNA polymerase

Answer 17

Synthesizes DNA strands

Question 18

Elongation

DNA polymerase can only attach nucleotides to a pre-existing

Answer 18

3’ OH group

Question 19

Elongation

Synthesized using

Answer 19

dNTP

Question 20

Elongation

DNA and RNA synthesis occurs in the

Answer 20

5’–>3’ direction

Question 21

Elongation

DNA polymerase 1,3 used in

Answer 21

Replication

Question 22

Elongation

Primers synthesis

Answer 22

Primase (a RNA polymerase) makes RNA primers

Joins with helicase at replication fork

Question 23

Elongation

DNA polymerase III

Answer 23

Synthesizes DNA from 5’ to3’ direction

Attaches new nucleotides to 3’ OH sugar phosphate backbone

Has 3’ to 5’ exonuclease activity (corrects errors)

Question 24

Elongation

Leading strand

Answer 24

Being synthesized towards the fork

One continuous DNA strand

5’ to 3’

Question 25

Elongation Lagging strand

Answer 25

DNA synthesized away from fork Discontinuous DNA strands called Okazaki fragment 5' to 3'

Question 26

Elongation DNA polymerase 1

Answer 26

Synthesizes DNA strand in 5' to 3' direction Also has 3' to 5' and 5' to 3' exonuclease activity Removes RNA primers and replaces them with DNA Only on lagging strand

Question 27

Elongation DNA ligase

Answer 27

After replacement by DNA poly 1, a gap still remains which is filled by DNA ligase Joins Okazaki Fragments together

Question 28

Termination

Answer 28

DNA replication ends when two replication forks meet Additionally, some organisms contain specific termination sequence (Ter) that stops DNA replication

Question 29

How is DNA replication accuracy achieved

Answer 29

Low error in base pair selection by DNA polymerase Proofreading by DNA polymerase Mismatch repair occurs soon after DNA replication

Question 30

Mismatch repair system

Answer 30

Abnormalities in DNA secondary structures recognized by mismatch repair system Gets rid of nucleotides on new DNA strand