A4 epigenetic regulation of gene expression Flashcards
are all genes switched on at the same time
no, the genes that are expressed are different in different cell types
eg neuron vs heart cell
what is epigenetics
an additional level of gene expression regulation
plays a major role in determining which genes are expressed in different cells
what is CpG
a rare dinucleotide
based on guanine/cytosine (G/C) content of genome (42%)
CpG cytosine and guanine are on the same strand of DNA
what is the frequency of CpG
should occur with ~4.4% freq
reality just 1% is observed
why is CpG notation used
used to distinguish this linear5’-C-phosphate-G-3’ from the CG base pairing of cytosine and guanine in double-stranded DNA
what are areas of the genome with a high density of CpGs called
CpG islands
where are CpG islands often found
promoter region of genes
how do CpG dinucleotides have some role in gene expression regulation
because CpG dinucleotides can be chemically modifed and this alters transcription factor binding to DNA
how can CpG be chemically modified
and what is the product, enzymatic regulation
methylation
5-methyl cytosine
DNMT
DNA methyltransferase
result of promoter (=CpG island) methylation often do
alter gene expression
by what mechanism do CpG islands able to prevent gene expression
methylation
methyl binding proteins bind to methylated DNA preventing binding of transcription factors
what enzymes methylate DNA
methyltransferase
what are the two types of DNA methylation
maintenance methylation
de novo methylation
maintenance methylation
ensures methylation patterns are preserved as cells divide
de novo
allows different methylation patterns during development
