Chapter 16 Vocabulary

antiparallel

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

Chromatin

The complex of DNA and proteins that makes up eukaryotic chromosomes.

DNA ligase

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).

DNA polymerase

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.

DNA replication

The process by which a DNA molecule is copied

Euchromatin

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

Heterochromatin

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

Helicase

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

leading strand

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

lagging strand

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

mismatch repair

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

nuclease

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.

nucleotide excision repair

A repair system that removes and then correctly replaces a damaged segment of DNA using the undamaged strand as a guide.

Okazaki fragment

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.

origin of replication

Site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides.

primase

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

Primer

A short stretch of RNA with a free 3′ end, bound by complementary base pairing to the template strand and elongated with DNA nucleotides during DNA replication

replication fork

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

semiconservative model

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.

single-strand binding protein

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.

Telomere

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

topoisomerase

A protein that breaks, swivels, and rejoins DNA strands. It helps to relieve strain in the double helix ahead of the replication fork

Transformation

A change in genotype and phenotype due to the assimilation of external DNA by a cell, can result in horizontal gene transfer if from another species.

virus

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, a membranous envelope.