BIO 103: Ch. 16 - DNA, The Genetic Material

Nucleotide

The building blocks (monomers) of a nucleic acid, consisting of a five-carbon sugar (deoxyribose or ribose) covalently bonded to a nitrogenous base (adenine, cytosine, guanine, thymine, or uracil) and one to three phosphate groups.

Double Helix

The form of native DNA, referring to its 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 in opposite 5' - 3' directions).

DNA Replication

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

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.

Origin of Replication

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

Replication Fork

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

Helicase

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

Primer

A short polynucleotide 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 the 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 the replication fork) by the addition of nucleotides to the 3' end of an existing chain. There are several different DNA polymerases; DNA polymerase III and DNA polymerase I play major roles in DNA replication in E. coli.

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.

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.

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).

Telomere

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

Chromatin

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

Histone

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.

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.