Bio 111 lecture 18
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28 Terms
what are epigenetic modifications?
modifications that change the expression of genes without changing the DNA sequence of the gene
what structure do epigenetic changes often change?
chromatin structure
epigenetic modifications can change how tightly ____ and _____ bind to each other
DNA, histones
how many states of chromatin are there?
2
what are the states of chromatin?
euchromatin
heterochromatin
in which state of chromatin are DNA and histones tightly associated?
heterochromatin
in which state of chromatin is DNA very accessible to transcription factors/RNA polymerase binding?
euchromatin
what is chromatin remodeling?
changes to the state of chromatin due to epigenetic modifications
what part of histone proteins extend out from the nucleosome core?
the amino acid terminals
what is histone acetylation?
acetyl groups are covalently bound to lysines in the amino-terminal tails of histones
what does the added acetyl group do to acetylated histones?
negates the positive charge of the lysine
what do Histone Acetyl Transferases do?
acetylate histoneswh
what do Histone Deacetylases do?
deacetylate histones
what is hyperacetylation?
high levels of acetylation
what does hyperacetylation lead to?
histones less positively charged
are relaxed chromatin genes more or less likely to be expressed?
more
what is DNA methylation?
a methyl group is added to cytosines in DNA to form 5-methylcytosine
what does the methyl group in DNA methylation do?
serves as a physical barrier to the binding of transcription factors, which inhibits gene transcription
what enzyme methylates cytosines?
DNA methyl transferases(DNMTs)
what are cytosines demethylated by?
DNA demethylases
are all cytosines methylated?
no
which cytosines are methylated?
cytosines followed by a guanine
5’ CG 3’
what are CpG islands?
CG-rich regions of DNA
where are CpG islands most often located?
promoter regions
changes in the levels of histone acetylation and DNA methylation combine to __________________________
remodel chromatin and affect gene transcription
changes in the levels of _____________ and _________ combine to remodel chromatin and affect gene transcription
histone acetylation
DNA methylation
does euchromatin promote or inhibit gene transcription?
promoted
oes heterochromatin promote or inhibit gene transcription?
inhibit