Chapter 16

Question 1

transformation

Answer 1

a change in genotype and phenotype due to assimilation of foreign DNA

Question 2

replication fork

Answer 2

a Y-shaped region wherenew DNA strands are elongating

Question 3

helicases

Answer 3

are enzymes that untwist the double helix at the replication forks

Question 4

single-strand binding proteins

Answer 4

bind to and stabilize single-stranded DNA

Question 5

topoisomerase

Answer 5

Topoisomerase corrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA strands

Question 6

primase

Answer 6

an enzyme that can start an RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template
-primer is short (5-10 nucleotides long) and the 3’ end is the starting point for DNA strand

Question 7

DNA polymerases

Answer 7

catalyze the elongation of new DNA at a replication fork

-usually requires a primer and DNA template strand

Question 8

Antiparallel Elongation

Answer 8

The antiparallel structure of the double helix affects replication
DNA polymerases add nucleotides only to the free 3′ end of a growing strand; therefore, a new DNA strand can elongate only in the 5′ to 3′ direction

Question 9

leading strand

Answer 9

Along one template strand of DNA, the DNA polymerase synthesizes a leading strand continuously, moving toward the replication fork

Question 10

lagging strand

Answer 10

To elongate the other new strand, called the lagging strand, DNA polymerase must work in the direction away from the replication fork

Question 11

okazaki fragments

Answer 11

The lagging strand is synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase

Question 12

nucleotide excision repair

Answer 12

a nuclease cuts out and replaces damaged stretches of DNA

Question 13

evolutionary significance of altered DNA nucleotides

Answer 13

Error rate after proofreading repair is low 
Sequence changes can be passed on to the next generation
These changes (mutations) are the source of the genetic variation

Question 14

telomeres

Answer 14

Eukaryotic chromosomal DNA molecules have special nucleotide sequences at their ends called telomeres
Telomeres do not prevent the shortening of DNA molecules, but they do postpone the erosion of genes near the ends of DNA molecules
shortening of telomeres is connected to aging

Question 15

telomerase

Answer 15

An enzyme called telomerase catalyzes the lengthening of telomeres in germ cells

Question 16

chromatin

Answer 16

In the eukaryotic cell, DNA is precisely combined with proteins in a complex called

Question 17

bacterial chromosome

Answer 17

is a double-stranded, circular DNA molecule associated with a small amount of protein