Chapter 14: DNA Structure and Function

electrophoresis

technique used to separate DNA fragments according to size

exonuclease

enzymes that cleave nucleotides one at a time from the end of a polynucleotide chain

helicase

during replication, this enzyme helps to open up the DNA helix by breaking the hydrogen bonds

induced mutation

mutation that results from exposure to chemicals or environmental agents

lagging strand

during replication, the strand that is replicated in short fragments and away from the replication fork

leading strand

strand that is synthesized continuously in the 5'-3' direction which is synthesized in the direction of the replication fork

ligase

enzyme that catalyzes the formation of a phosphodiester linkage between the 3' OH and 5' phosphate ends of the DNA

mismatch repair

type of repair mechanism in which mismatched bases are removed after replication

mutation

variation in the nucleotide sequence of a genome

nucleotide excision repair

type of DNA repair mechanism in which the wrong base, along with a few nucleotides upstream or downstream, are removed

Okazaki fragment

DNA fragment that is synthesized in short stretches on the lagging strand

point mutation

mutation that affects a single base

primase

enzyme that synthesizes the RNA primer; the primer is needed for DNA pol to start synthesis of a new DNA strand

primer

short stretch of nucleotides that is required to initiate replication; in the case of replication, the primer has RNA nucleotides

proofreading

function of DNA pol in which it reads the newly added base before adding the next one

replication fork

Y-shaped structure formed during initiation of replication

silent mutation

mutation that is not expressed

single-strand binding protein

during replication, protein that binds to the single-stranded DNA; this helps in keeping the two strands of DNA apart so that they may serve as templates

sliding clamp

ring-shaped protein that holds the DNA pol on the DNA strand

spontaneous mutation

mutation that takes place in the cells as a result of chemical reactions taking place naturally without exposure to any external agent

telomerase

enzyme that contains a catalytic part and an inbuilt RNA template; it functions to maintain telomeres at chromosome ends

telomere

DNA at the end of linear chromosomes

topoisomerase

enzyme that prevents overwinding of DNA when DNA replication is taking place

transformation

process in which external DNA is taken up by a cell

transition substitution

when a purine is replaced with a purine or a pyrimidine is replaced with another pyrimidine

transversion substitution

when a purine is replaced by a pyrimidine or a pyrimidine is replaced by a purine