Kapitel 5

Question 1

One of several alternative forms of a gene. In a diploid cell - each gene will typically have two alleles - occupying the corresponding position (locus) on homologous chromosomes.

Answer 1

allele

Question 2

DNA repair pathway in which single faulty bases are removed from the DNA helix and replaced. Compare nucleotide excision repair. (Figure 5–41)

Answer 2

base excision repair

Question 3

Protein complex that utilizes ATP hydrolysis to load the sliding clamp on to a primer–template junction in the process of DNA replication.

Answer 3

clamp loader

Question 4

A type of DNA recombination that takes place between short - specific sequences of DNA and occurs without the gain or loss of nucleotides. It does not require extensive homology between the recombining DNA molecules.

Answer 4

conservative site-specifc recombination

Question 5

Enzyme that is involved in opening the DNA helix into its single strands for DNA replication.

Answer 5

DNA helicase

Question 6

Enzyme that joins the ends of two strands of DNA together with a covalent bond to make a continuous DNA strand.

Answer 6

DNA ligase

Question 7

Enzyme that synthesizes DNA by joining nucleotides together using a DNA template as a guide.

Answer 7

DNA polymerase

Question 8

Enzyme that synthesizes a short strand of RNA on a DNA template - producing a primer for DNA synthesis. (Figure 5–10)

Answer 8

DNA primase

Question 9

A set of processes for repairing the many accidental lesions that occur continually in DNA.

Answer 9

DNA repair

Question 10

Enzyme that binds to DNA and reversibly breaks a phosphodiester bond in one or both strands. Topoisomerase I creates transient single-strand breaks - allowing the double helix to swivel and relieving superhelical tension. Topoisomerase II creates transient double-strand breaks - allowing one double helix to pass through another and thus resolving tangles. (Figures 5–21 and 5–22)

Answer 10

DNA topoisomerase (topoisomerase)

Question 11

Transposable element that exists as DNA throughout its life cycle. Many move by cut-and-paste transposition.

Answer 11

DNA-only transposon

Question 12

Process by which DNA sequence information can be transferred from one DNA helix (which remains unchanged) to another DNA helix whose sequence is altered. It often accompanies general recombination events. (Figure 5–59)

Answer 12

gene conversion

Question 13

A cell in the germ line of an organism - which includes the haploid gametes and their specified diploid precursor cells. Germ cells contribute to the formation of a new generation of organisms and are distinct from somatic cells - which form the body and leave no descendants.

Answer 13

germ cell

Question 14

Protein that binds free histones - releasing them once they have been incorporated into newly replicated chromatin. (Figure 4–27)

Answer 14

histone chaperone (chromatin assembly factor)

Question 15

X-shaped structure observed in DNA undergoing recombination - in which the two DNA molecules are held together at the site of crossing-over - also called a cross-strand exchange. (Figure 5–55)

Answer 15

Holliday junction (cross-strand exchange)

Question 16

Genetic exchange between a pair of identical or very similar DNA sequences - typically those located on two copies of the same chromosome. Also a DNA repair mechanism for double-strand breaks. (Figures 5–48 - 5–50 - and 5–54)

Answer 16

homologous recombination (general recombination)

Question 17

In molecular biology - the process whereby two complementary nucleic acid strands form a base-paired duplex DNA-DNA - DNA-RNA - or RNA-RNA molecule. Forms the basis of a powerful technique for detecting specific nucleotide sequences. (Figures 5–47 and 8–33)

Answer 17

hybridization

Question 18

One of the two newly synthesized strands of DNA found at a replication fork. The lagging strand is made in discontinuous lengths that are later joined covalently. (Figure 5–7)

Answer 18

lagging strand

Question 19

One of the two newly synthesized strands of DNA found at a replication fork. The leading strand is made by continuous synthesis in the 5′-to-3′ direction. (Figure 5–7)

Answer 19

leading strand

Question 20

The result of errant homologous recombination that uses the homolog from the other parent instead of the sister chromatid as the template - converting the sequence of the repaired DNA to that of the other homolog.

Answer 20

loss of heterozygosity

Question 21

Heritable change in the nucleotide sequence of a chromosome. (Panel 8–1 - pp. 478–481)

Answer 21

mutation

Question 22

The rate at which changes (mutations) occur in DNA sequences.

Answer 22

mutation rate

Question 23

A DNA repair mechanism for double-strand breaks in which the broken ends of DNA are brought together and rejoined by DNA ligation - generally with the loss of one or more nucleotides at the site of joining.

Answer 23

nonhomologous end joining

Question 24

Type of transposable element that moves by being first transcribed into an RNA copy that is converted to DNA by reverse transcriptase then inserted elsewhere in the genome. The mechanism of insertion differs from that of the retroviral-like transposons. (Table 5–4 - p. 288)

Answer 24

nonretroviral retrotransposons

Question 25

Type of DNA repair that corrects damage of the DNA double helix - such as that caused by chemicals or UV light - by cutting out the damaged region on one strand and resynthesizing it using the undamaged strand as template. Compare base excision repair. (Figure 5–41)

Answer 25

nucleotide excision repair

Question 26

Large protein complex that is bound to the DNA at origins of replication in eukaryotic chromosomes throughout the cell cycle. (Figure 5–31)

Answer 26

origin recognition complex (ORC)

Question 27

The use of conservative site-specific recombination to control the expression of particular genes. The ability of S. typhimurium bacterium - for example - to alternate between two types of flagella using consecutive site-specific recombination.

Answer 27

phase variation

Question 28

Eukaryotic protein that catalyzes synapsis of DNA strands during genetic recombination. Called RecA in E. coli.

Answer 28

Rad51

Question 29

Prototype for a class of DNA-binding proteins that catalyze synapsis of DNA strands during genetic recombination. (Figure 5–49)

Answer 29

RecA (RecA protein)

Question 30

Y-shaped region of a replicating DNA molecule at which the two strands of the DNA are being separated and the daughter strands are being formed. (Figures 5–7 and 5–18)

Answer 30

replication fork

Question 31

A large family of transposons that move themselves in and out of chromosomes by a mechanism similar to that used by retroviruses - being first transcribed into an RNA copy that is converted to DNA by reverse transcriptase then inserted elsewhere in the genome. (Table 5–4 - p. 288)

Answer 31

retroviral-like retrotransposons

Question 32

RNA-containing virus that replicates in a cell by first making an RNA–DNA intermediate and then a double-strand DNA molecule that becomes integrated into the cell’s DNA. (Figure 5–62)

Answer 32

retrovirus

Question 33

Enzyme first discovered in retroviruses that makes a double-strand DNA copy from a single-strand RNA template molecule.

Answer 33

reverse transcriptase

Question 34

Short stretch of RNA synthesized on a DNA template. It is required by DNA polymerases to start their DNA synthesis.

Answer 34

RNA primer

Question 35

Period of a eukaryotic cell cycle in which DNA is synthesized. (Figure 17–4)

Answer 35

S phase

Question 36

Protein that binds to the single strands of the opened-up DNA double helix - preventing helical structures from reforming while the DNA is being replicated. (Figure 5–15)

Answer 36

single-strand DNA-binding (SSB) protein

Question 37

Protein complex that holds the DNA polymerase on DNA during DNA replication. (Figure 5–17)

Answer 37

sliding clamp

Question 38

Any cell of a plant or animal other than cells of the germ line. From Greek soma - body.

Answer 38

somatic cell

Question 39

Reaction in which one of the single-strand 3′ ends from one duplex DNA molecule penetrates another duplex and searches it for homologous sequences through base-pairing. Also called strand invasion.

Answer 39

strand exchange

Question 40

A proofreading system that removes DNA replication errors missed by the DNA polymerase proofreading exonuclease. Detects the potential for DNA helix distortion from noncomplementary base pairs then recognizes and excises the mismatch in the newly synthesized strand and resynthesizes the excised segment using the old strand as a template.

Answer 40

strand-directed mismatch repair

Question 41

Enzyme that elongates telomere sequences in DNA - which occur at the ends of eukaryotic chromosomes.

Answer 41

telomerase

Question 42

Segment of DNA that can move from one genome position to another by transposition. (Table 5–4 - p. 288)

Answer 42

transposable element (transposon)

Question 43

Movement of a DNA sequence from one genome site to another. (Table 5–4 - p. 288)

Answer 43

transposition (transpositional recombination)