Chapter 12

Question 1

semiconservative replication

Answer 1

each original nucleotide strand remains intact (conserved) despite being removed from the molecule; the original DNA molecule is half (semi) conserved during replication

one round of replication produces two hybrid molecules, each containing 1/2 of the original DNA and 1/2 new DNA; each round of replication produces more and more new DNA and only a few hybrid molecules

Question 2

replication origin

Answer 2

sequence of nucleotides where replication is initiated

bacterial chromosomes have a single replication origin whereas eukaryotic chromosomes contain many

Question 3

replication bubble

Answer 3

a loop generated by the unwinding of the double helix undergoing replication

Question 4

replication fork

Answer 4

the point of unwinding, where the 2 single nucleotide strands separate from the double-stranded DNA helix

Question 5

bidirectional replication

Answer 5

if there are 2 replication forks, (one at each end of the replication bubble) the forks proceed outward in both directions

Question 6

DNA polymerase

Answer 6

the enzyme that synthesizes DNA; can add nucleotides to the 3’ end of the growing strand

Question 7

continuous replication

Answer 7

replication of the leading strand in the same direction as that of the unwinding; allowing new nucleotides to be added continuously to the 3’ end of the new strand as the template is exposed

Question 8

leading strand

Answer 8

DNA strand that is replicated continuously

Question 9

discontinuous replication

Answer 9

replication of the lagging strand in the direction opposite the direction of unwinding; this means that the DNA must be synthesized in short stretches

Question 10

lagging strand

Answer 10

DNA strand that is replicated discontinuously

Question 11

okazaki fragments

Answer 11

the short lengths of DNA produced by discontinuous replication of the lagging strand; the fragments on the lagging strand are linked together to create a continuous new DNA molecule

Question 12

DNA helicase

Answer 12

breaks the hydrogen bonds that exist between the bases of the two nucleotide strands of a DNA molecule

Question 13

single-strand binding proteins

Answer 13

proteins that tightly attach to the exposed single-strand DNA; they protect the nucleotide chains and prevent the formation of secondary structures that interfere with replication

Question 14

topoisomerase

Answer 14

an enzyme that adds or removes rotations in a DNA helix by temporarily breaking down nucleotide strands; controls supercoiling in DNA

Question 15

DNA gyrase

Answer 15

a topoisomerase that receives the torque that builds up ahead of the replication fork as a result of unwinding

Question 16

primase

Answer 16

an enzyme that synthesizes primers to begin DNA replication

Question 17

primers

Answer 17

short stretches of nucleotides; required at the 5’ end of the leading strand; must be generated at teh beginning of each okazaki fragment

Question 18

DNA ligase

Answer 18

catalyzes the formation of a phosphodiester bond without adding another nucleotide to the strand

Question 19

proofreading

Answer 19

ability of DNA polymerases to remove and replace incorrectly placed nucleotides in teh course of replication

Question 20

mismatch repair

Answer 20

corrects errors after replication is complete

Question 21

replication liscensing factors

Answer 21

proteins that ensure that replication takes place only once at each origin; required at the origin before replication can be initiated and removed after the DNA has been replicated

Question 22

telomerase

Answer 22

an enzyme with both a protein and an RNA component; present in single cell organisms, germ cells, embryonic cells, etc.