DNA Replication and Enzyme Functions

This set of flashcards covers the essential enzymes and processes involved in DNA replication, including the synthesis of leading and lagging strands.

Helicase

An enzyme that unwinds the parental double helix at the replication fork by breaking the hydrogen bonds, separating the parental strands and making them available as template strands.

Single-strand binding protein

A protein that binds to the unpaired DNA strands to prevent them from repairing during replication.

Topoisomerase

An enzyme that helps relieve strain by breaking, swiveling, and rejoining DNA strands.

Primase

An enzyme that synthesizes an RNA primer from the $5'$ to $3'$ direction.

DNA polymerase III

An enzyme that catalyzes the synthesis of a new DNA strand by adding nucleotides to the $3'$ end of the RNA primer.

DNA polymerase I

An enzyme that removes RNA nucleotides of the primer from the $5'$ end and replaces them with DNA nucleotides added to the $3'$ end of the adjacent fragment.

DNA ligase

An enzyme that joins Okazaki fragments into a continuous DNA strand by forming phosphodiester bonds.

Leading strand

A complementary DNA strand synthesized continuously by DNA polymerase III in the $5'$ to $3'$ direction towards the replication fork, requiring only one RNA primer.

Lagging strand

A DNA strand synthesized discontinuously away from the replication fork as a series of segments called Okazaki fragments, requiring more than one RNA primer.

Okazaki fragments

Series of short DNA segments that are synthesized discontinuously to form the lagging strand.

Direction of Elongation

The process where a new DNA strand can elongate only in the $5'$ to $3'$ direction because DNA polymerase III adds nucleotides only to the free $3'$ end.