DNA replication/recombination ch 7

Semiconservative replication

The mechanism of DNA replication in which each daughter double helix retains one intact parental strand and acquires one newly synthesized complementary strand.

Meselson-Stahl experiment

The 1958 experiment using density gradient centrifugation with heavy (15N15N) and light (14N14N) nitrogen isotopes that confirmed the semiconservative model of DNA replication.The experiment utilized bacteria to demonstrate that after one round of replication, the DNA consisted of hybrid strands, supporting the semiconservative replication theory.

Direction of DNA synthesis

The obligatory 5′→3′ direction in which DNA polymerases assemble nucleotides by adding incoming dNTPs to the free 3′-OH3′-OH group of the nascent strand.

Helicase

The enzyme that unwinds the double helix at the replication fork by breaking hydrogen bonds between base pairs.

Single-strand binding proteins (SSBs)

Proteins that stabilize separated single template strands to prevent reannealing during replication.

Primase

An RNA polymerase that synthesizes short complementary RNA primers to supply the initial 3′-OH3′-OH end required for DNA polymerases to begin elongation.

DNA Polymerase III

The primary prokaryotic replication enzyme that catalyzes phosphodiester bond formation to elongate both leading and lagging strands.

Leading strand

The daughter DNA strand synthesized continuously toward the progressing replication fork in the 5′→3′ direction.

Lagging strand

The daughter DNA strand synthesized discontinuously away from the replication fork as a series of short segments.

Okazaki fragments

Short stretches of newly synthesized DNA formed discontinuously on the lagging strand template.

Topoisomerase

The enzyme that relaxes torsional strain and supercoils ahead of the advancing replication fork by cleaving and resealing the sugar-phosphate backbone

DNA Polymerase I

The prokaryotic enzyme that excises RNA primers and replaces them with complementary DNA nucleotides during the polishing phase.

DNA Ligase

The enzyme that forms covalent phosphodiester bonds between adjacent Okazaki fragments, sealing nicks in the sugar-phosphate backbone.