DNA Replication

Question 1

Explain why DNA replication is semiconservative

Answer 1

when the double helix unwinds it exposes bases on each strand, each of these strands can act as a template for synthesis of new strands, the new strands form by insertion of complementary base pairing, single double helix becomes two identical daughter double helixes

Question 2

what 3 phases does DNA replication happen in?

Answer 2

Initiation, elongation, and termination

Question 3

Describe initiation

Answer 3

Initiator Protein binds to Ori. Single stranded binding proteins open up the double helix to prepare it for complementary base pairing, helicase unwinds the helix, primase adds (synthesizes) RNA primer. Two replication forks are formed

Question 4

What proteins open up the double helix and prepare it for complementary base pairing in initiation?

Answer 4

single stranded binding proteins

Question 5

where does initiation occur?

Answer 5

At the origins (ORI) of replication. In plasmids this is just one location, in chromosomes it’s many locations

Question 6

Why do we need RNA primer?

Answer 6

So that DNA polymerase can add nucleotide sequences on

Question 7

Primers are _____ and ______ to each template strand

Answer 7

complementary and antiparallel

Question 8

What is the purpose of initiation?

Answer 8

preparation of double helix for complementary base pairing

Question 9

What are the 4 main steps in elongation?

Answer 9

• DNA polymerase III catalyzes phosphodiester bond formation between adjacent nucleotides, this is called polymerization
• DNA polymerase I replaces RNA primer with DNA sequence
• DNA ligase covalently joins successive Okazaki fragments together (that have nicks in the backbone)
• DNA topoisomerase may need to reduce supercoiling by cutting DNA phosphate backbone to let unwind ahead of replication fork

Question 10

What is the phosphodiester bond?

Answer 10

The link in DNA between a 5’ and 3’

Question 11

Catalyze

Answer 11

to cause an action or process to begin

Question 12

Synthesize

Answer 12

to form _____ by combining parts or elements

Question 13

DNA polymerase

Answer 13

Catalyzes new phosphodiester bonds

Question 14

what do I mean when I say ‘catalyzes new phosphodiester bonds’?

Answer 14

Nucleotides are matched based on base pairing then attached to form new DNA strand

Question 15

what are DNA polymerase reactants?

Answer 15

high-energy dNTPs (nucleotide triphosphates)

Question 16

what is elongation doing in one sentence?

Answer 16

Makes sure the correct nucleotide sequence is copied from template strand to newly synthesized strand of DNA

Question 17

DNA synthesis new strand goes from?

Answer 17

5’ to 3’

Question 18

The template and newly synthesized strands are…

Answer 18

antiparallel

Question 19

why is it important to use nucleotide triphosphates instead of nucleotide monophosphates when catalyzing new phosphodiester bonds?

Answer 19

because these high energy dNTP provide the energy for the formation for the phosphodiester bonds. Monophosphates don’t have enough energy

Question 20

What does DNA topoisomerase do?

Answer 20

Relaxes supercoils by cutting the sugar phosphate backbone bonds strands of DNA. Once it does this it can rotate the cut site and rejoin ends, the unwound broken strands are then sealed by ligase

Question 21

What is termination?

Answer 21

A releasing of the DNA and the component enzymes. No proteins involved

Question 22

How many replication forks depart from an origin of replication?

Answer 22

Two

Question 23

The step in DNA replication in which the replication proteins open up the double helix and prepare for complementary base pairing is called

Answer 23

initiation

Question 24

a group of enzymes that seals nicks in the phosphodiester backbone and is very important in the lagging strand replication

Answer 24

ligases

Question 25

the group of enzymes able to relax supercoils in DNA is called

Answer 25

topoisomerases