AP BIO CH 16

Bacteriophage

A virus that infects bacteria; also called a phage.

DNA ligase

A linking enzyme essential for DNA replication; catalyzes the covalent bonding of the 3' end of a new DNA fragment to the 5' end of a growing chain.

DNA Polymerase

An enzyme that catalyzes the elongation of new DNA at a replication fork by the addition of nucleotides to the existing chain

double helix

The form of native DNA, referring to its two adjacent polynucleotide strands wound into a spiral shape.

helicase

An enzyme that untwists the double helix of DNA at the replication forks

lagging strand

A discontinuously synthesized DNA strand that elongates in a direction away from the replication fork.

leading strand

The new continuous complementary DNA strand synthesized along the template strand in the mandatory 5' ( 3' direction.

mismatch repair

The cellular process that uses special enzymes to fix incorrectly paired nucleotides.

nuclease

An enzyme that hydrolyzes DNA and RNA into their component nucleotides.

nucleotide excision repair

The process of removing and then correctly replacing a damaged segment of DNA using the undamaged strand as a guide.

Okazaki fragment

A short segment of DNA synthesized on a template strand during DNA replication. Many Okazaki fragments make up the lagging strand of newly synthesized DNA.

origin of replication

Site where the replication of a DNA molecule begins.

phage

A virus that infects bacteria; also called a bacteriophage.

primase

An enzyme that joins RNA nucleotides to make the primer.

primer

A polynucleotide with a free 3´ end, bound by complementary base pairing to the template strand, that is elongated during DNA replication.

replication fork

A Y-shaped region on a replicating DNA molecule where new strands are growing.

semiconservative model

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

single-strand binding protein

During DNA replication, molecules that line up along the unpaired DNA strands, holding them apart while the DNA strands serve as templates for the synthesis of complementary strands of DNA.

telomerase

An enzyme that catalyzes the lengthening of telomeres. The enzyme includes a molecule of RNA that serves as a template for new telomere segments.

telomere

The protective structure at each end of a eukaryotic chromosome. Specifically, the tandemly repetitive DNA at the end of the chromosome's DNA molecule. See also repetitive DNA.

topoisomerase

A protein that functions in DNA replication, helping to relieve strain in the double helix ahead of the replication fork.

transformation

(1) The conversion of a normal animal cell to a cancerous cell. (2) A change in genotype and phenotype due to the assimilation of external DNA by a cell.