Chapter 13 vocab

DNA replication

DNA replication

The process by which a DNA molecule is copied; also called DNA synthesis

Origins of replications

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

Helicase

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

Replication fork

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

Double helix

The form of native DNA, referring to its two adjacent antiparallel polynucleotide strands wound around an imaginary axis into a spiral shape.

Single-stranded 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.

Semiconservative model

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

Toposiomerase

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

Primer

A short stretch of RNA with a free 3’ end, bound by complementary base pairing to the template strands and elongated with DNA nucleotides during DNA replicaiton.

Primase

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

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.

There are several of these; “thing'“ 3 and “thing” 1 play major roles in DNA replication in E. coli.

Leading strand

THe new complementary DNA strands synthesized continuously along the template strand toward the replication fork in the mandatory 5’ —> 3’ direction.

Lagging strand

A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5’ —> 3’ direction away from the replication fork.

Okazaki gragments

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.

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)

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 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 un-damaged strand as a guide.

Telomerase

An enzyme in cells that helps keep them alive by adding DNA to telomeres (the ends of chromosomes). Each time a cell divides, the telomeres lose a small amount of DNA and become shorter.

Nucleoid

A non-membrane-enclosed region in a prokaryotic cell where its chromosome is located.

Chromatin

THe complex of DNA and proteins that makes up eukaryotic chromosomes. When the cell is not dividing, chromatin exists in its dispersed form. as a mass of very long, thin fibers that are not visible with a light microscope.

Heterochromatin

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

Euchromatin

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