Regulation of Eukaryotic Chromosomes Flashcards
what are the two histone variants of h3
h3.3 and cenpa/ cenh3
what are the four core histones
h3, h2a, h4 and h2b
centromeres are characterised by a centromere specific histone h3 variant called
cenpa or cenh3
centromeres often have heterochromatin that is rich in what
satellite DNA sequences
what is chromatin remodeling
the energy dependent displacement or reorganisation of nucleosomes that occurs in conjunction with activation of genes for transcription
remodeling complexes can do what to nucleosomes
alter, slide or displace nucleosomes
there are numerous ___ dependent chromatin remodeling complexes
ATP
list three histone post translational modifications
lysine methylation, lysine acetylation, lysine ubiquitilation
histone tails are highly
conserved
what is a direct effect of modifying amino acid side chains on histone tails
a change in charge
what is an indirect effect of modifying amino acid side chains on histone tails
recruitment
methylation of lysines is done by
histone methyltransferases
demethylation of lysines is done by
histone demethyltransferases
acetylation of lysines is done by
histone acetyltransferases
deacetylation of lysines is done by
histone deacetylase
acetylation of lysine residues in histone tails results in
a loss of positive charge to neutral charge
when lysine is acetylated, the loss of positive charge results in
a reduction in binding to DNA, opening up of chromatin and access to DNA
histone modification enzymes are targeted to specific genomic regions how?
through transcription activators
lysines being acetylated causes transcriptional
activation
methylation of lysine residues is context dependent, they can recruit
activators or repressors of transcription
methylation of lysine 9 on histone h3 results in
heterochromatin assembly and transcriptional silencing
what recognises methylated lysines
chromodomains
what recognises acetylated lysines?
bromodomains
what is the fifth base?
5-methylcytosine
what catalyses the reaction of the addition of a methyl group to cytosine
DNA methyltransferases
roughly how many CpGs in human somatic cells are methylated
70-80% referred to as global methylated
where do the greatest amount of CpG methylations occur
in satellite DNA, repetitive elemtns,
in some areas CpGs are unmethylated what are these called
CpG islands
about how many CpG islands exist in the human genome
45,000
where are unmethylated CpG islands located
in the promoters, first exons of 50-60% of human genes
CpG islands are present in nearly all
active housekeeping genese
what does DNA methylation do?
it compacts chromatin and is associated with transcriptional repression
