BIOL 4610: Chromatin

Chromatin

Combination of our DNA and associated proteins

Histone complex is composed of two copies of __

Core histones

A key feature of histone complex:

Many positively charged amino acids facing the outside

The positively charged amino acids of histone complexes are crucial for __

Binding to DNA

Nucleosome

Combination of DNA wrapped around a histone complex

Core histone proteins:

H2A, H2B, H3, H4

__ a non-core histone protein that helps stabilize DNA on the nucleosome

H1

Linker DNA

The regions of DNA between nucleosomes

Euchromatin

Long linker DNA and increased spacing between nucleosomes

Heterochromatin

Shorter linker DNA between nucleosomes in more condensed form

__ can prevent loosening of DNA or loosen the grip of histone complex on DNA

Chemical groups

Heterochromatin structure:

Blocks RNA polymerase from gaining access to DNA, preventing transcription

Euchromatin structure:

Allows RNA polymerase and transcription factors to access and transcribe the genes

Histone code

A unique set of histone PTMs at various regions of chromosomes regulate gene expression

All histone modifications are __

Reversible

Histone Acetylation

• Carried out by HATs

• Addition of acetyl groups to lysine on histone tails

• Positive charge is neutralized

• Grip on the negative DNA loosens, promotes formation of less-dense euchromatin

Histone Methylation:

• Carried out by HMTs

• Addition of methyl groups to lysine on histone tails

• Blocks acetylation and prevents loosening of DNA

• Marks regions of repetitive DNA

Regions high in __ are heterochromatin and contain repressed genes

Heterochromatin

Chromatin can alter between euchromatin and heterochromatin by adding and removing __

Histone modifications