Th2L01 Modification of histones

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Modification of histones

Tails are vulnerable to

covalent modifications esp. addition or removal of acetyl,

phosphate or methyl groups by enzymes in the nucleus

Little affect on individual

nucleosomes but can affect the stability of the chromatin fibre or higher

order structures

Attract specific enzymes

which can either condense or decondense the chromatin

These proteins

signal things e.g. new replications has occurred; these genes need to be

expressed

Histone enzymes

Tightly regulated

Brought to a particular

region with specific cues esp. interactions with proteins that bind to

specific sequences of DNA; work with chromatin-remodelling complexes

Histones enzymes

RNA polymerase

An enzyme that links

together the growing chain of RNA nucleotides during transcription, using

a DNA strand as a template.

Histone acetyltransferase

(HAT)

recruit transcriptional

co-activators, act in large complexes, recruit RNA polymerase, turn on

gene expression

Lead to the uncoiling of

chromatin

Histone deacetylase (HDAC) -

proteins that function to

remove acetyl groups from histones, which closes chromatin conformation

and decreases gene expression

Heterochromatin

DNA that is densely packed

around histones

The genes in heterochromatin

are generally inaccessible to enzymes and are turned off.

Euchromatin

DNA that is loosely packed

around histones

This DNA is more accessible

to enzymes and the genes in euchromatin can be activated if needed.

Methylation

A chemical modification of

DNA that does not affect the nucleotide sequence of a gene but makes that

gene less likely to be expressed