Gene expression Flashcards
what are transcription factors?
proteins that bind to DNA and affect how the RNA polymerase binds
role: stimulate transcription of a gene
define epigenetics
the process by where environmental factors can cause heritable changes in gene function without changing the DNA base sequence
organisation of DNA in eukaryotic cells
DNA is wrapped around proteins called histones->
nucleosomes coiled into a chromatin fibre ->
further condensation of chromatin ->
duplicated chromosome
what is epigenome
the epigenome is a second layer formed by chemical tags that cover both DNA and histones. It determines the shape of the DNA-histone complex- it keeps genes that are inactive in a tightly packed arrangement
why is the epigenome flexible?
the chemical tags respond to environmental changes.
what is the epigenome of a cell
the accumulation of the signals it has received during its life time and therefore acts like a cellular memory
what is acetylation of histones
activation/inhibition of a gene
what is methylation of DNA
add/remove methyl groups on the NDA by attracting enzymes
if there is a weak association of histones with DNA, what happens?
weak association
DNA histone complex (chromatin) is less condensed
DNA is accessible by transcription factors
mRNA is produced
gene on
if there is a strong association of histones with DNA, what happens?
strong association
DNA histone complex (chromatin) is more condensed
DNA not accessible by transcription factors
mRNA not produced
gene off
how do you inhibit transcription
by condensing the DNA histone complex by:
decreased acetylation of histones
increased methylation of DNA
how does decreased acetylation of histones inhibit transcription
the +charges on the histones increases.
increases their attraction to the phosphate groups of DNA
therefore association is stronger
how does increased methylation of histones inhibit transcription
prevents the binding of TFs to DNA
or
attracts proteins that condense the DNA histone complex (by inducing deacetylation of histones)
therefore making DNA inaccessible to TFs
how do you promote transcription
increased acetylation
decreased methylation
