Chapter 6.4: DNA Replication

Question 1

What is the function of DNA helicase in DNA replication?

Answer 1

• DNA helicase unwinds the double helix

Question 2

What is the function of DNA ligase in DNA replication?

Answer 2

 During elongation, the DNA ligase enzyme welds together Okazaki fragments

Question 3

What is the function of single-stranded DNA binding proteins in DNA replication?

Answer 3

• A special group of single-stranded DNA binding proteins keep the DNA helix open

Question 4

What are replication forks?

Answer 4

o The antiparallel strands of DNA unwind gradually at the two Y-shaped areas called the replication forks

Question 5

What does DNA polymerase do?

Answer 5

o With energy released from severing the triphosphate arm of a dNTP substrate molecule, the DNA polymerase enzyme catalyzes the formation of a new phosphodiester bond

Question 6

What is a template in DNA replication?

Answer 6

o Each of the two separated DNA strands acts as template, a molecular mold, for the synthesis of a new second strand

Question 7

What is the function of primase in DNA replication?

Answer 7

• An enzyme called primase generates RNA primers to initiate DNA synthesis

Question 8

What causes supercoiling?

Answer 8

 Movement of replication fork causes more and more supercoiling

Question 9

Define supercoiling

Answer 9

o The additional twisting of the DNA molecule

Question 10

What are the 3 requirements for DNA polymerase action?

Answer 10

 The 4 dNTPs  A single stranded template. Double-stranded DNA must be unwound, and DNA polymerases moves along the template in the 3’-to-5’ direction  A primer with a free 3’ hydroxyl group

Question 11

What happens during initiation of DNA replication?

Answer 11

which proteins open up the double helix and prepare it for complementary base pairing

Question 12

What is the function of DNA topoisomerases?

Answer 12

 DNA topoisomerases help relax the supercoils by cleaving the sugar-phosphate backbone between two adjoining nucleotides

Question 13

What is the function of telomeres?

Answer 13

o Telomeres ensure the maintenance and accurate replication of the two ends of each linear chromosome

Question 14

What is complementary base pairing?

Answer 14

o The newly replicated strands form as complementary bases align opposite the exposed bases on the two parental strands (A-T, G-C) in a process known as complementary base pairing

Question 15

What is the function of DNA polymerase III in DNA replication?

Answer 15

 DNA Polymerase III plays a major role in producing the new strands of complementary DNA

Question 16

In what direction does DNA synthesis happen?

Answer 16

5’ to 3’

Question 17

What is the function of DNA polymerase I in DNA replication?

Answer 17

 DNA Polymerase I fills in the gaps between newly synthesized Okazaki segments

Question 18

Describe the “Heavy” Nitrogen Experiments to Demonstrate Semiconservative Replication

Answer 18

Question 19

What is the difference between the leading and lagging strand?

Answer 19

 One newly synthesized strand (the leading strand) can grow continuously into each of the opening forks  The other new strand (the lagging strand), made at the same fork but synthesized from the other template strand, is generated in pieces called Okazaki fragments as more and more template is unwound at the fork

Question 20

What is semiconservative replication?

Answer 20

o Double helix duplication is called semiconservative replication: a copying in which one strand of each new double helix is conserved from the parent molecule and the other is newly synthesized

Question 21

In what direction does replication happen?

Answer 21

 Replication is generally bidirectional, with the replication forks moving in opposite directions as unwinding proceeds

Question 22

What happens during elongation of DNA replication?

Answer 22

proteins connect the correct sequence of nucleotides on both newly formed DNA double helixes