DNA Replication

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

Transformation

A change in genotype and phenotype due to the assimilation of external DNA by a cell

Bacteriophage

A virus that infects bacteria

Double Helix

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

Antiparallel

Referring to the arrangement of the sugar-phosphate backbones in a DNA double helix. They run opposite 5' --> 3'

Chromatin

The complex of DNA and proteins that make up eukaryotic chromosomes. When the cell is no dividing, this exists in a dispersed form

DNA ligase

A linking enzyme that is essential for the DNA replication; catalyzes the covalent bonding of the 3' end of one DNA fragment to the 5' end of another fragment

DNA polymerase

An enzyme that catalyzes the elongation of new DNA by the addition of nucleotides to the 3' end of an existing chain

Euchromatin

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

Histones

A small protein with a high proportion of positively charged amino acids that binds to the negatively charged DNA and plays a key role in chromatin structure

Heterochromatin

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

Helicases

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

Lagging Strand

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

Leading Strand

The new complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory 5' --> 3' direction

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

Nucleosome

The basic, beadlike unit of DNA packing in eukaryotes, consisting of a segment of DNA wound around a protein core composed of two copies of each of the four types of histone

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 fragments

A short segment of DNA synthesized away from the replication fork on a template strand during DNA replication. These segments are joined together to make up the lagging strand of newly synthesized DNA

Origins of Replication

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

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

Primase

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

Replication fork

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

Single Stranded Binding Proteins

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

A 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

Telomeres

The tandemly repetitive DNA at the end of a eukaryotic chromosomes DNA molecule. They protect the organisms genes from being eroded during successive rounds of replication.

Topoisomerase

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

Virus

An infectious particle incapable of replicating outside of a cell, consisting of an RNA or DNA genome surrounded by a protein coat and, for some, a membranous envelope