epigenetics Flashcards
epigentics is the study of ____ that are….
study of heritable changes in gene expression that are NOT due to changes in DNA sequence
comparison b/w genetic & epigenetic phenomena
mendelian genetics:
phenotype = mutant
genotype = mutant
epigenetics:
phenotype = mutant
genotype = wildtype
3 common epigenetic mechanisms
1- DNA methylation (a subset of cytosine residues could be modified by methylation)
2- histone modification/histone variants
3- regulatory non-coding RNAs (ncRNA or RNAi)
gene silencing
during early embryogenesis there is a random inactivation of one X chromosome in females so as to prevent the overexpression of X chromosomal genes
consequence –> one allele is expressed in some areas of the body & the other allele is expressed in other areas
typically, the sites of DNA methylation are on the ___ site of…
5C site of cytosine in CpG dinucleotides
why is epigenetics important? 3 kinds of frequent epigenetic changes have been identified in tumors
1- genome-wide hypomethylation
2-tumor-suppressor genes can be inactivated by dense hypermethylation of their upstream regulatory sequences
3- loss of parental imprinting
2 distinct types/patterns of methylation
1- maintenace - (methyltransferases)
2- De novo - (methyltransferases, highly expressed at embryo implantations when waves of de novo methylation are occurring in the genome)
the knockout of any methyltransferase genes is ___ during early development or shortly thereafter
lethal
imprinting is the epigenetic process where…
one of the parental alleles is silenced (maternal or paternal)
methylation can block ___ of a gene, similar to a mutation in that gene
transcription (expression)
detection of methylated cytosine in DNA - once DNA has been treated (bisulfite conversion occurs), then it can be distinguished by ___, ___, or ___
PCR
sequencing
methylation specific enzymes
while DNA methylation is widespread in plants, fungi, and animals, it has been curiously lost/low in some of the most well studied genetic organisms including ___ and ____
yeast & C. elegans
some of the most methylated sequences found within genomes are ____
transposable elements
histone modifications change ___ structure affecting ___ of DNA
chromatin
accessibility
2 mechanisms of histone modification
acetylation
methylation
euchromatin are ___ compact and ___ transcribed
less
actively
heterochromatin are ___ compact and ___
more
transcriptionally inactive
heterochromatic DNA is often ____, while histones are ____ and ___ on residues associated with transcriptional repression
methylated
hypoacetylated & methylatd
non-coding RNAs are proposed to control ___ via sequence-specific interactions with ___ regions
___RNAs and ___RNAs bind and & inactivate transcription
gene expression
regulatory
microRNAs & short interfering RNAs
small RNA(sRNA) appear to cause/direct ___ of specific genes
methylation
how many different microRNA genes are there?
LOTS, it is hard to find accurate numbers, but likely thousands
single miRNAs can potentially target >100 diff mRNAs so each can have huge influence on transcription
can multiple epigenetic mechanisms interact?
yes they all interact together
- histones are methylated
- heterochromatin is activated by RNAi
