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double helix
The form of native DNA, referring to its two adjacent antiparallel polynucleotide strands wound around an imaginary axis into a spiral shape.
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origins of replication
Site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides.
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topoisomerase
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.
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antiparallel
Referring to the arrangement of the sugar-phosphate backbones in a DNA double helix (they run in opposite 5′ → 3′ directions).
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DNA polymerase
an enzyme that catalyzes the elongation of new DNA at a replication fork by the addition of nucleotides to the existing chain
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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).
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chromatin
The complex of DNA and proteins that makes up a eukaryotic chromosome. 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.
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replication fork
A Y-shaped region on a replicating DNA molecule where the parental strands are being unwound and new strands are growing.
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RNA primer
A short stretch of RNA with a free 3' end, bound by complementary base pairing to the template strand, that is elongated with DNA nucleotides during DNA replication.
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RNA primase
An enzyme that joins RNA nucleotides to make the primer using the parental DNA strand as a template.
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Leading strand
The new complementary DNA strand synthesized continuously along the template strand toward the replication fork in the mandatory 5'?3' direction.
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telomere
The tandemly repetitive DNA at the end of a eukaryotic chromosome's DNA molecule that protects the organism's genes from being eroded during successive rounds of replication. See also repetitive DNA.
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template strand
The DNA strand that provides the pattern, or template, for ordering the sequence of nucleotides in an RNA transcript.
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helicase
An enzyme that untwists the double helix of DNA at the replication forks, separating the two strands and making them available as template strands.
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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.
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Okazaki fragment
A short segment of DNA synthesized away from the replication fork on a template strand during DNA replication, many of which are joined together to make up the lagging strand of newly synthesized DNA.
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Single-strand DNA-binding protein (SSBPs)
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.
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telomerase
An enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells.
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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.
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nucleoid
A dense region of DNA in a prokaryotic cell.
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DNA polymerase I
5' to 3' exonuclease activity, removal of RNA primers.
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DNA polymerase III
5' to 3' polymerase activity, 3' to 5' exonuclease activity (delete key)
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Sliding clamp protein
oads DNA polymerase on the DNA and keeps DNA polymerase from falling. Increase processivity.
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