AP Bio Unit 6: DNA Replication & Enzymes

Helicase

An enzyme that untwists the double helix of DNA at the replication forks.

Topoisomerase

Enzyme that functions in DNA replication, helping to relieve strain in the double helix ahead of the replication fork.

Primase

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

DNA Polymerase 3 (DNAP 3)

Attaches to each primer on the parental strand and moves in the 3' - 5' direction adding nucleotides to the new strand.

DNA Polymerase 1 (DNAP 1)

Converts the RNA primers to DNA nucleotides

Single Stranded Binding Proteins (SSBPs)

Proteins that bind to DNA to keep it open and from reconnecting during replication.

Leading Strand

The new continuous complementary DNA strand synthesized along the template strand 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.

DNA Ligase

An enzyme that joins Okazaki Fragments together forming a continuous DNA strand.

Okazaki Fragments

Small fragments of DNA produced on the lagging strand during DNA replication, joined later by DNA ligase to form a complete strand.

Replication Fork

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

Semi-conservative Replication

Method of DNA replication in which parental strands separate, act as templates, and produce molecules of DNA with one parental DNA strand and one new DNA strand