epigenetics

what does epigenetics involve

changes in gene function, without changes to the base sequence of dna

what is the epigenome

all chemical modifications to all histone proteins + dna in an organism

in eukaryotic cells, where do we find DNA in the nucleus?

wrapped around proteins called histone

how can histone proteins be chemically modified

addition of acetyl groups

how can dna be chemically modified

addition of methyl groups without changing the base sequence

are the epigenome and genome heritable?

yes

what is the difference between what the epigenome and genome can do

epigenome can undergo change

why do identicaly twins become more distinguishable with age?

same dna, epigenomes change independently = differences

what are changes in the epigenome caused by?

changes in the environment like smoking, stress, exercise, diet, internal signalling from the bodys cells

what does the chemical modification of histones control? what does this result in?

how tightly the dna is bound- intermolecular bonding between histones + DNA changes. if DNA wound more tightly in certain area, genes in this section switched off- gene + promotor regions hidden from transcription factors and RNA polymerase

is the modification of histones reversible and irreversible? what does this mean?

reversible therefore can be different in different cell types and can vary with age

what does this image show

dna wrapped around histone proteins which form a nucleosome, which coil tightly around each other to form chromosome structure

explain the process of acetylation of histones

lysine has positively charged R group which forms ionic bonds with negatively charged phosphate backbone of DNA. adding acetyl groups (COCH3) to lysine amino acids on histone proteins removes the positive ion and therefore removes a bond between the histone protein and the DNA. results in dna wrapping less tightly around the histones

when DNA is less tightly wrapped around the histones, what happens to RNA polymerase and transcription factors?

RNA polymerase and transcription factors can bind more easily and gene expression is switched on

what does removal of acetyl groups (deacetylation) cause?

inhibits transcription

explain the methylation of DNA

methyl groups (CH3) added to carbon molecule on cytosine bases. this suppresses transcription of the affected gene. this is because methylated bases attract proteins that bind to the dna and inhibit transcription