Biology topic 8 Epigenetics flash cards (1)

What is epigenetics?

Changes in gene function that occur without any changes to the DNA base sequence

What is the epigenome?

The complete set of chemical modification to all histone proteins and the DNA in an organism excluding changes to the base sequence

How is DNA organised in eukaryotic cells?

DNA is wrapped around a histone protein to form structures called nucleosomes

What is a nucleosome and what does it do?

Its a structed formed when DNA wraps around a histone protein

Nucleosomes coil tightly together to form a the structure of a chromosome

What chemical modification can occur on histone proteins?

Acetylation which is the addition of acetyl groups (COCH3) to lysine amino acids on histone proteins

What is a chemical modification in epigenetics?

A small chemical change added to or removed from DNA or histone protein that alters gene expression without changing the DNA base sequence

What chemical modification can occur on DNA?

Methylation which is the addition of methyl groups to cytosine bases, particularly in regions contain multiple cytosine and guanine bases

Why do identical twins become more different with age?

Identical twins have the same DNA but their epigenomes change independently over time leading to differences in gene expression (because they experience different environments e.g diet and stress)

What environmental factors can cause epigenetic changes?

Smoking

Stress

Exercise

Diet

What internal factors can cause epigenetic changes?

Internal signalling (chemical signals sent between cells) from the body’s cells can trigger epigenetic modifications

How do chemical modifications affect DNA winding around histones?

Chemical modification alter the intermolecular bonding between DNA and histones

This changes how tightly DNA is wound around histone proteins

What is intermolecular bonding and how is it effected by chemical modification?

Its the attraction between negatively charged DNA and positively charged histone proteins

Acylation removes the positive charge from lysine

This weakens the bonds causing DNA to becomes less tightly wound and transcription can occur

What is lysine?

An amino acid in histones

What happens when DNA is wound tightly around histones?

Genes in the region are switched off

The gene and promoter regions become less accessible to transcription factors and RNA polymers

Why is histone modification reversible ?

Chemical groups can be added or removed , meaning histone modification can vary between cell types and change with age

What is the effect of histone acetylation?

DNA becomes less tightly wrapped around histones

RNA polymerase and transcription factors can bind more easily

Gene expression is switched on

What is histone acetylation?

The addition of acetyl groups to lysine

Why does acetylation loosen DNA histone binding?

Lysine normally has positively charged R group, which forms ionic bonds with the negatively charged backbone

Adding acetyle groups removes the positive charge, reducing the ionic bonding

This results in DNA being held less tightly