Chapter 9: DNA Replication and Recombination

Vocabulary flashcards covering prokaryotic and eukaryotic DNA replication mechanisms, essential enzymes, and fidelity systems from Chapter 9.

Conservative replication

A model of DNA replication proposing that the original double-stranded DNA molecule remains entirely intact while serving as a template for a completely new double helix.

Dispersive replication

A model of DNA replication proposing that both strands of both daughter DNA molecules contain scattered, interspersed segments of original and newly synthesized DNA.

Semiconservative replication

A model of DNA replication in which each resulting daughter double helix consists of one original parental strand and one newly synthesized strand.

Replicon

A segment of DNA that undergoes replication from a single origin of replication to its completion point.

Replication bubble

A loop formed when double-stranded DNA unwinds at an origin of replication, enabling simultaneous synthesis on both exposed template strands.

Leading strand

The newly synthesized strand of DNA that undergoes continuous replication in the same direction as the movement of the unwinding replication fork.

Lagging strand

The newly synthesized strand of DNA that undergoes discontinuous replication in short segments in the direction opposite to replication fork unwinding.

Okazaki fragments

Short, discontinuously synthesized DNA segments on the lagging strand, measuring $1000\text{--}2000$ nucleotides long in bacteria and $100\text{--}200$ nucleotides long in eukaryotes.

Initiator proteins (DnaA)

Proteins that bind to the origin of replication ($oriC$) in bacteria, unwinding a short stretch of DNA to allow helicase entry.

DNA Helicase

An enzyme that breaks hydrogen bonds between nitrogenous bases to unwind double-stranded DNA ahead of replication.

Single-strand-binding proteins

Proteins that attach to exposed single-stranded DNA to prevent the strands from reannealing before replication takes place.

DNA Gyrase

A type II topoisomerase that relieves torsional strain and supercoiling ahead of the replication fork by making double-stranded breaks in the DNA.

Primase

An RNA polymerase that synthesizes short RNA primers, supplying the free $3'\text{-OH}$ group required by DNA polymerases to initiate synthesis.

DNA Polymerase III

The main bacterial replication enzyme, responsible for elongation with $5' \rightarrow 3'$ polymerase activity and proofreading via $3' \rightarrow 5'$ exonuclease activity.

DNA Polymerase I

A bacterial DNA polymerase that removes RNA primers using $5' \rightarrow 3'$ exonuclease activity and fills in the resulting gaps using $5' \rightarrow 3'$ polymerase activity.

DNA Ligase

An enzyme that seals nicks in the sugar-phosphate backbone by forming a phosphodiester bond between a $3'\text{-OH}$ group and an adjacent $5'\text{-P}$ group.

Replication licensing factor

A eukaryotic protein that binds to origins of replication early in the cell cycle to ensure that DNA replication is initiated only once per cell cycle.

DNA Polymerase $\alpha$

A eukaryotic DNA polymerase complexed with primase activity that synthesizes a short RNA primer followed by a short string of DNA nucleotides.

DNA Polymerase $\delta$

A eukaryotic DNA polymerase that completes synthesis on the lagging strand.

DNA Polymerase $\epsilon$

A eukaryotic DNA polymerase responsible for replicating the leading strand.

Telomeres

Repetitive, G-rich sequences located at the terminal ends of eukaryotic chromosomes that protect linear chromosomes from shortening during replication.

Telomerase

A enzyme containing an internal RNA component ($15\text{--}22$ nucleotides) that serves as a template to extend the $3'$ overhang of eukaryotic telomeres.