chapter 16

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

A virus that infects bacteria; also called a phage.

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.

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).

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 different DNA polymerases; DNA polymerase III and DNA polymerase I play major roles in DNA replication in E. coli.

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

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

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

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

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

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.

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

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

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.

The basic, bead-like unit of DNA packing in eukaryotes, consisting of a segment of DNA wound around a protein core composed of two copies of each of four types of histone.

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.

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

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.

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

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.

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.

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 replication. See also repetitive DNA.

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.

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 viruses, a membranous envelope.