Dna Replication

Front 1

Replication fork

Back 1

Y-shaped region where the parental strands of DNA are being unwound

Front 2

Helicase

Back 2

An enzyme that unwinds and separates the parental DNA strands at the replication fork

Front 3

Single-strand binding protein

Back 3

Binds to unpaired DNA strands after they have been separated by helicase, in order to keep them from rejoining

Front 4

Topoisomerase

Back 4

Breaks, swivels and rejoins DNA parental strands ahead of the replication fork to relieve the strain caused by the untwisting of the double helix

Front 5

RNA primer

Back 5

The initial (RNA) nucleotide chain produced during DNA synthesis; grows in 5' to 3' direction, along the DNA template from 3' to 5'; new DNA strand starts on the 3' end of the primer

Front 6

Primase

Back 6

Synthesises RNA primer using parental DNA strand as a template

Front 7

DNA polymerases

Back 7

Enzymes that catalyse the synthesis of new DNA by adding nucleotides to a preexisting chain

Front 8

DNA polymerase I

Back 8

Replaces RNA primers with DNA

Front 9

DNA polymerase III

Back 9

In E. coli, DNA pol III adds a DNA nucleotide to the RNA primer, then continues to add complementary DNA nucleotides to the DNA template strand

Front 10

Leading strand

Back 10

The strand of parental DNA which is synthesised continuously, requiring only one primer to initiate the process

Front 11

Lagging strand

Back 11

The strand of parental DNA that is synthesised discontinuously, in a series of Okazaki fragments (which each require a primer)

Front 12

DNA ligase

Back 12

Forms a bond between Okazaki fragments

Front 13

Telomeres

Back 13

Nucleotide sequences at the end of eukaryotic chromosomal DNA molecules that do not contain genes

- prevent the mechanisms that activate when DNA damage is detected, leading to cell cycle arrest or cell death

- act as buffer zone that protects against the effects of gene shortening