epigenetic control of gene expression

What is epigenetics

• environmental factors can cause heritable changes in genes function without changing base sequences of dna

environmental influences such as …

diet, toxins, stress, smoke, drinking

what are dna and histones covered in? what do they form?

chemical tags that form a second layer to the epigenome

what does the epigenome determine

the shape of the dna-histone complex

describe the main difference between dna code and epigenome and explain why this is the case

dna code is fixed, whilst epigenome is flexible, because chemical tags respond to environmental changes

what can the environmental factors do when attached to the protein

• acetylation of histones (activate or inhibit gene)

• methylation of dna by attracting enzymes that can add or remove methyl groups

What happens when the association of dna with histones is stronger and what can you conclude from this?

• the dna-histone complex is more condensed, do dna is not accessible by transcriptional factors so cannot initiate production of mrna, so genes are switched off.

• condensation of dna-histone complex inhibits transcription, due to decreased acetylation of histones and methylation of dna

what is acetylation

when an acetyl group is transferred to a molecule (by acetylcoenzyme A)

What does decreasing acetylation of histones do?

increase positive charges on histones and increasing their attraction to phosphate groups on dna. (More condensed + attracted)

what is methylation

addition of a methyl group to a molecule, where a methyl group is added to the cytosine bases of dna

how can methylation inhibit transcription

• prevent binding of transcriptional factors to dna

• attracting proteins that condense dna -histone complex so cannot bind to transcriptional factors

If epigenetics do not alter sequence of bases on dna , what do they do instead

increase incidence of mutations

how can drugs be used in epigenetics to activate or silence certain genesu

• drugs can inhibit enzymes involved in histone acetylation or dna methylation

• specifically target cancer cells

how can the development of diagnostic tests help treat diseases

• early stage detection

• identify level of dna methylation or histone acetylation

• this allows seeking of early treatment and better chance of cure

what molecule is involved in breaking down mrna

small interfering RNA (siRNA)

describe how a small interfering RNA operates in breaking down mRNA to stop transcription

• an enzyme cuts a double stranded RNA molecule into smaller sections called siRNA

• one of the two siRNA strands combines with an enzyme

• this guides the enzyme to an mRNA by pairing up bases with complementary ones on section of mrna molecule

• the enzyme cuts the mRNA into smaller sections, so no translation into polypeptide occurs, gene is not expressed and is therefore blocked