Kapitel 5 Flashcards
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.
allele
DNA repair pathway in which single faulty bases are removed from the DNA helix and replaced. Compare nucleotide excision repair. (Figure 5–41)
base excision repair
Protein complex that utilizes ATP hydrolysis to load the sliding clamp on to a primer–template junction in the process of DNA replication.
clamp loader
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.
conservative site-specifc recombination
Enzyme that is involved in opening the DNA helix into its single strands for DNA replication.
DNA helicase
Enzyme that joins the ends of two strands of DNA together with a covalent bond to make a continuous DNA strand.
DNA ligase
Enzyme that synthesizes DNA by joining nucleotides together using a DNA template as a guide.
DNA polymerase
Enzyme that synthesizes a short strand of RNA on a DNA template - producing a primer for DNA synthesis. (Figure 5–10)
DNA primase
A set of processes for repairing the many accidental lesions that occur continually in DNA.
DNA repair
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)
DNA topoisomerase (topoisomerase)
Transposable element that exists as DNA throughout its life cycle. Many move by cut-and-paste transposition.
DNA-only transposon
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)
gene conversion
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.
germ cell
Protein that binds free histones - releasing them once they have been incorporated into newly replicated chromatin. (Figure 4–27)
histone chaperone (chromatin assembly factor)
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)
Holliday junction (cross-strand exchange)
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)
homologous recombination (general recombination)
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)
hybridization
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)
lagging strand
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)
leading strand
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.
loss of heterozygosity
Heritable change in the nucleotide sequence of a chromosome. (Panel 8–1 - pp. 478–481)
mutation
The rate at which changes (mutations) occur in DNA sequences.
mutation rate
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.
nonhomologous end joining
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)
nonretroviral retrotransposons
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)
nucleotide excision repair
Large protein complex that is bound to the DNA at origins of replication in eukaryotic chromosomes throughout the cell cycle. (Figure 5–31)
origin recognition complex (ORC)
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.
phase variation
Eukaryotic protein that catalyzes synapsis of DNA strands during genetic recombination. Called RecA in E. coli.
Rad51
Prototype for a class of DNA-binding proteins that catalyze synapsis of DNA strands during genetic recombination. (Figure 5–49)
RecA (RecA protein)
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)
replication fork
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)
retroviral-like retrotransposons
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)
retrovirus
Enzyme first discovered in retroviruses that makes a double-strand DNA copy from a single-strand RNA template molecule.
reverse transcriptase
Short stretch of RNA synthesized on a DNA template. It is required by DNA polymerases to start their DNA synthesis.
RNA primer
Period of a eukaryotic cell cycle in which DNA is synthesized. (Figure 17–4)
S phase
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)
single-strand DNA-binding (SSB) protein
Protein complex that holds the DNA polymerase on DNA during DNA replication. (Figure 5–17)
sliding clamp
Any cell of a plant or animal other than cells of the germ line. From Greek soma - body.
somatic cell
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.
strand exchange
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.
strand-directed mismatch repair
Enzyme that elongates telomere sequences in DNA - which occur at the ends of eukaryotic chromosomes.
telomerase
Segment of DNA that can move from one genome position to another by transposition. (Table 5–4 - p. 288)
transposable element (transposon)
Movement of a DNA sequence from one genome site to another. (Table 5–4 - p. 288)
transposition (transpositional recombination)
