Chapter 13: The Molecular Basis of Inheritance

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

bacteriophages (phages)

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

double helix

Answer 5

the form of native DNA, referring to its two adjacent antiparallel polynucleotide strands wound around an imaginary axis into a spiral shape

Question 6

antiparallel

Answer 6

referring to the arrangement of the sugar-phosphate backbones in a DNA double helix (they run in opposite 5’ to 3’ directions).

Question 7

semiconservative model

Answer 7

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 8

replication fork

Answer 8

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

Question 9

helicases

Answer 9

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

Question 10

single-strand binding proteins

Answer 10

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 11

topoisomerase

Answer 11

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 12

primer

Answer 12

a short polynucleotide with a free 3’ end, bound by complementary base pairing to the template strand and elongated with DNA molecules during DNA replication

Question 13

primase

Answer 13

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

Question 14

DNA polymerases

Answer 14

an enzyme that catalyzes the elongation of new DNA (for example, at a replication fork) by the addition of nucleotides to the 3’ end of an existing chain. there are several different DNA polymerases; DNA polymerase III and DNA polymerase I play major roles in DNA replication in E. coli.

Question 15

leading strand

Answer 15

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

Question 16

lagging strand

Answer 16

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

Question 17

Okazaki fragments

Answer 17

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 18

DNA ligase

Answer 18

a linking enzyme essential for DNA replication; catalyzes the covalent bonding of the 3’ end of one DNA fragment (such as an Okazaki fragment) to the 5’ end of another DNA fragment (such as a growing DNA chain)

Question 19

mismatch repair

Answer 19

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

Question 20

nuclease

Answer 20

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

Question 21

telomeres

Answer 21

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

Question 22

nucleoid

Answer 22

a non-membrane-enclosed region in a prokaryotic cell where its chromosome is located

Question 23

chromatin

Answer 23

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 24

histones

Answer 24

proteins that are responsible for the first level of DNA packing in chromatin.

Question 25

nucleosome

Answer 25

the basic unit of DNA packing

Question 26

heterochromatin

Answer 26

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

Question 27

euchromatin

Answer 27

the less condensed form of eukaryotic chromatin that is available for transcription