DNA Replication

DNA replication

The process by which DNA is copied to produce two identical DNA molecules

Central dogma of molecular biology

Describes the flow of genetic information from DNA to RNA to protein

Semi-conservative replication

Each new DNA molecule contains one original strand and one newly synthesised strand

Purines

Nitrogenous bases with two rings, adenine and guanine

Pyrimidines

Nitrogenous bases with one ring, cytosine and thymine

Origin of replication (oriC)

Specific DNA sequence where DNA replication begins

Pre-replication complex

Group of proteins that assemble at the origin of replication to initiate DNA replication

DnaA protein

Binds to the origin of replication and causes local unwinding of DNA

A-T rich region

Region of DNA that separates easily due to fewer hydrogen bonds

Helicase (DnaB)

Enzyme that unwinds and separates the DNA double helix at the replication fork

Replication fork

Y-shaped structure formed when DNA is unwound for replication

Topoisomerase

Enzyme that relieves supercoiling tension ahead of the replication fork

Topoisomerase I

Relieves tension by nicking one strand of DNA

Topoisomerase II (DNA gyrase)

Relieves tension by cutting and rejoining both DNA strands

Single-strand binding proteins

Stabilise single-stranded DNA and prevent re-annealing

Primase

Synthesises short RNA primers complementary to the DNA template

RNA primer

Short RNA sequence that provides a free 3’ OH group for DNA synthesis

DNA polymerase III

Main enzyme that synthesises new DNA strands in the 5’ to 3’ direction

DNA template strand

The original DNA strand used to guide synthesis of a complementary strand

5’ to 3’ synthesis

Direction in which DNA polymerases add nucleotides to a growing DNA strand

3’ OH group

Chemical group required by DNA polymerase to add nucleotides

Leading strand

DNA strand synthesised continuously in the same direction as replication fork movement

Lagging strand

DNA strand synthesised discontinuously opposite to replication fork movement

Okazaki fragments

Short DNA fragments synthesised on the lagging strand

Discontinuous DNA synthesis

DNA synthesis that occurs in fragments rather than continuously

DNA polymerase I

Removes RNA primers and replaces them with DNA

Exonuclease activity

Ability of DNA polymerase I to remove nucleotides, including RNA primers

DNA ligase

Enzyme that seals gaps between Okazaki fragments by forming phosphodiester bonds

RNA-DNA hybrid

Intermediate molecule formed when RNA primers are attached to newly synthesised DNA

Replication bubble

Region of DNA opened around the origin where replication occurs

Circular genome

DNA structure typical of bacteria that replicates from a single origin

Linear genome

DNA structure typical of eukaryotes with multiple origins of replication