Chapter 6: DNA Replication and Repair

Question 1

Each strand of DNA can serve as a _________, for the synthesis of a new complementary strand.

Answer 1

template, or mold

Question 2

Because each parental strand serves as the tem- plate for one new strand, each of the daughter DNA double helices ends up with one of the original (old) strands plus one strand that is completely new; this style of replication is said to be ___________.

Answer 2

semiconservative

Question 3

the two DNA strands are locked together firmly by the large numbers of __________ between the bases on both strands

Answer 3

hydrogen bonds

Question 4

The process of DNA synthesis is begun by initiator proteins that bind to specific DNA sequences called __________.

Answer 4

replication origins

Question 5

DNA molecules in the process of being replicated contain Y-shaped junctions called ______.

Answer 5

replication forks

Question 6

The two forks move away from the origin in opposite directions, unzipping the DNA double helix and copying the DNA as they go. DNA replication—in both bacterial and eukaryotic chromosomes—is therefore termed __________.

Answer 6

bidirectional

Question 7

The movement of a replication fork is driven by the action of the replication machine, at the heart of which is an enzyme called ________.

Answer 7

DNA polymerase

Question 8

This enzyme catalyzes the addition of nucleotides to the 3ʹ end of a grow- ing DNA strand, using one of the original, parental DNA strands as a template

Answer 8

DNA polymerase

Question 9

The polymerization reaction involves the formation of a phosphodiester bond between the 3ʹ end of the growing DNA chain and the 5ʹ-phosphate group of the incoming nucleotide, which enters the reaction as a __________.

Answer 9

deoxyribonucleoside triphosphate

Question 10

small DNA pieces

Answer 10

Okazaki fragments

Question 11

The DNA strand that is made discontinuously in this way is called the ________.

Answer 11

lagging strand

Question 12

the other strand, which is synthesized continuously, is called the __________.

Answer 12

leading strand

Question 13

when DNA polymerase does make a rare mistake and adds the wrong nucleotide, it can correct the error through an activity called _____.

Answer 13

proofreading

Question 14

takes place at the same time as DNA synthesis.

Answer 14

proofreading

Question 15

This proofreading mechanism is possible only for DNA polymerases that synthesize DNA exclusively in the _______ direction.

Answer 15

5ʹ-to-3ʹ

Question 16

RNA fragment serves as a _____ for DNA synthesis, and the enzyme that synthesizes the RNA primer is known as ________.

Answer 16

primer; primase

Question 17

an enzyme that synthesizes RNA using DNA as a template.

Answer 17

primase

Question 18

A nuclease degrades the RNA primer, a DNA polymerase called a _______ replaces the RNA primers with DNA and the enzyme ____ joins the 5ʹ-phosphate end of one DNA fragment to the adjacent 3ʹ-hydroxyl end of the next

Answer 18

repair polymerase

DNA ligase

Question 19

For DNA replication to occur, the double helix must be continuously pried apart so that the incoming nucleoside triphosphates can form base pairs with each template strand. Two types of replication proteins—________________—cooperate to carry out this task.

Answer 19

DNA helicases and single-strand DNA-binding proteins

Question 20

produces a transient, single-strand nick in the DNA backbone, which temporarily releases the built-up tension; the enzyme then reseals the nick before falling off the DNA

Answer 20

DNA topoisomerase

Question 21

Back at the replication fork, an additional protein, called a ________, keeps DNA polymerase firmly attached to the template while it is synthesizing new strands of DNA.

Answer 21

sliding clamp

Question 22

hydrolyzes ATP each time it locks a sliding clamp around a newly formed DNA double helix

Answer 22

clamp loader

Question 23

Most DNA damage is only temporary, because it is immediately corrected by processes collectively called_______.

Answer 23

DNA repair

Question 24

loss of purine bases

Answer 24

depurination

Question 25

spontaneous loss of an amino group from a cytosine in DNA to produce the base uracil

Answer 25

deamination