Unit 6 - topic 2

Question 1

DNA replicates during

Answer 1

the S phase of the cell cycle

Question 2

3 alternative models for DNA replication

Answer 2

conservative
semi-conservative
dispersive

Question 3

conservative model

Answer 3

the parental strands direct synthesis of an entirely new double stranded molecule
the parental strands are fully conserved

Question 4

semi-conservative model

Answer 4

the two parental strands each make a copy of itself
after one round of replication, the two daughter cells each have one parental and one new strand

Question 5

dispersive model

Answer 5

material in the two parental strands in randomly dispersed between the two daughter molecules
after one round of replication, daughter molecules contain a random mix of parental and new DNA

Question 6

in 1954 Meselson and Stahl

Answer 6

performed an experiment using bacteria

Question 7

process of Meselson and Stahl’s experiment

Answer 7

1. bacteria was cultured with a heavy isotope, 15N
2. bacteria was transferred to a medium with a light isotope, 14N
3. DNA was centrifuged and analyzed after each replication

Question 8

by analyzing samples of DNA after each generation

Answer 8

it was found that the parental strands were following the semi-conservative model

Question 9

DNA replication begins at sites called

Answer 9

origins of replication

Question 10

various proteins will attach to the origin of replication and open the DNA to form a

Answer 10

replication fork

Question 11

replication fork

Answer 11

prime spot for action in DNA replication

Question 12

helicase

Answer 12

unwinds the DNA strands at each replication fork

Question 13

to keep the DNA from re-bonding with itself

Answer 13

proteins called single stranded binding proteins (SSBPs) bind to the DNA to keep it open

Question 14

topoisomerase

Answer 14

will help prevent strain ahead of the replication fork by relaxing supercoiling

Question 15

primase

Answer 15

an enzyme that initiates replication by adding short segments of RNA called primers to the parental DNA strand

Question 16

the enzymes that synthesize DNA can only attach new DNA nucleotides to

Answer 16

an existing strand of nucleotides

Question 17

primers serve as the

Answer 17

foundation for DNA synthesis

Question 18

DNA Polymerase III

Answer 18

attaches to each primer on the parental strand and moves in the 3’ to 5’ direction

Question 19

as DNAP III moves, it adds

Answer 19

nucleotides to the new strand in the 5’ to 3’ direction

Question 20

the DNAP III that follows helicase is known as the

Answer 20

leading strand and it only requires one primer

Question 21

the DNAP III on the parental strand that moves away from helicase is known as the

Answer 21

lagging strand and requires many primers

Question 22

leading strand

Answer 22

synthesized in one continuous segment

Question 23

since the lagging strand moves away from the replication fork

Answer 23

it is synthesized in chunks

Question 24

okazaki fragments

Answer 24

segments of the lagging strand

Question 25

after DNAP III forms an okazaki fragment

Answer 25

DNAP I replaces RNA nucleotides with DNA nucleotides

Question 26

DNA ligase

Answer 26

joins the okazaki fragments forming a continuous DNA strand

Question 27

since DNAP III can only add nucleotides to a 3' end

Answer 27

there is no way to finish replication on the 5' end of a lagging strand

Question 28

over many replications of DNA

Answer 28

the DNA will become shorter and shorter

Question 29

telomeres

Answer 29

repeating units of short nucleotide sequences that do not code for genes form a cap at the end of DNA to help postpone erosion

Question 30

telomerase

Answer 30

enzyme that adds telomeres to DNA

Question 31

as DNAP adds nucleotides to the new DNA strand

Answer 31

it proofreads the bases added

Question 32

if errors still occur

Answer 32

mismatch repair will take place enzymes remove and replace the incorrectly paired nucleotide

Question 33

if segments of DNA are damaged

Answer 33

nuclease can remove segments of nucleotides and DNAP and ligase can replace the segments