Chapter 16

Question 1

DNA replication

Answer 1

the process by which a DNA molecule is copied; also called DNA synthesis.

Question 2

Transformation

Answer 2

A change in genotype and phenotype due to the assimilation of external DNA by a cell. When the external DNA is from a member of a different species, transformation results in horizontal gene transfer.

Question 3

Bacteriophage

Answer 3

A virus that infects bacteria; also called a phage.

Question 4

Virus

Answer 4

An infectious particle incapable of replicating outside of a cell, consisting of an RNA or DNA genome surrounded by a protein coat (capsid) and, for some viruses, a membranous envelope.

Question 5

Semiconservative model

Answer 5

type of DNA replication in which the replicated double helix consists of one old strand, derived from the parental molecule, and one newly made strand.

Question 6

Origin of replication

Answer 6

Site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides.

Question 7

Replication fork

Answer 7

A Y-shaped region on a replication DNA molecule where the parental strands are being unwound and new strands are being synthesized.

Question 8

Helicase

Answer 8

An enzyme that untwists the double helix of DNA at replication forks, separating the two strands and making them available as template strands.

Question 9

Single-strand binding protein

Answer 9

A protein that binds to the unpaired DNA strands during DNA replication, stabilizing them and holding them apart while they serve as templates for the synthesis of complementary strands of DNA.

Question 10

Topoisomerase

Answer 10

A protein that breaks, swivels, and rejoins DNA strands. During DNA replication, topoisomerase helps to relieve strain in the double helix ahead of the replication fork.

Question 11

Primer

Answer 11

A short stretch of RNA with a free 3’ end, bound by complementary base pairing to the template strand and elongated with DNA nucleotides during DNA replication.

Question 12

Primase

Answer 12

An enzyme that joins RNA nucleotides to make a primer during DNA replication, using the parental DNA strand as a template.

Question 13

DNA polymerase

Answer 13

An enzyme that catalyzes the elongation of new DNA by the addition of nucleotides to the 3’ end of an existing chain.

Question 14

Leading strand

Answer 14

The new complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory 5’ S 3’ direction.

Question 15

Lagging strand

Answer 15

A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5’ S 3’ direction away from the replication fork.

Question 16

Okazaki fragment

Answer 16

A short segment of DNA synthesized away from the replication fork on a template strand during DNA replication. Many such segments are joined together to make up the lagging strand of newly synthesized DNA.

Question 17

DNA ligase

Answer 17

A linking enzyme essential for DNA replication; catalyzes the covalent bonding of the 3’ end of one DNA fragment to the 5’ end of another DNA fragment.

Question 18

Mismatch repair

Answer 18

The cellular process that uses specific enzymes to remove and replace incorrectly paired nucleotides.

Question 19

Nuclease

Answer 19

An enzyme that cuts DNA or RNA, either removing one of a few bases or hydrolyzing the DNA or RNA completely into its component nucleotides.

Question 20

Nucleotide excision repair

Answer 20

A repair system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide.

Question 21

Telomere

Answer 21

The tandemly repetitive DNA at the end of a eukaryotic chromosome’s DNA molecule. They protect the organism’s genes from being eroded during successive rounds of replication.

Question 22

Histone

Answer 22

A small protein with a high proportion of positively charged amino acids that binds to the negatively charged DNA and plays a key role in chromatin structure.

Question 23

Nucleosome

Answer 23

The basic, bead-like unit of DNA packing in eukaryotes, consisting of a segment of DNA wound around a protein core composed of two copies of each of four types of histone.

Question 24

Chromatic

Answer 24

The complex of DNA and proteins that makes up eukaryotic chromosomes. When the cell is not dividing, chromatin exists in its dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope.

Question 25

Heterochromatin

Answer 25

Eukaryotic chromatin that remains highly compacted during interphase and is generally not transcribed.

Question 26

Euchromatin

Answer 26

The less condensed form of eukaryotic chromatin that is available for transcription.