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Flashcards in Epigenetics Deck (22):
1

euchromatin vs. heterochromatin

euchromatin - electron poor, active

heterochromatin - electron dense, compacted, inactive

2

five currently known mechanisms of epigenetics

trithorax-group and polycomb-group proteins

DNA methylation

histone modifications

nuclear comparmentalization

non-coding RNA

3

histone H1

reduces negative charge of the DNA, so further condensation can occur

4

trithorax-group (trxG) and polycomb-group (PcG) proteins

trxG leads to gene expression

PcG leads to gene repression

PRC1 methylates histones

PRC2 binds because of methylation, leading to gene silencing

will stay there through mitosis and progeny

5

DNA methylation

the addition of a methyl group to the DNA base cytosine

tends to occur on CpG regions

6

Dnmt3a and 3b

carry out denovo methylation

3b is mostly near centromeres

3a is mostly for areas further from the centromeres

7

Dnmt 1

maintenance methyltransferase

8

CpG Islands

70-80% of CpG in the human genome are methylated, but CpG islands are mostly hypomethylated

50-60% of all human genes have CpG islands near their promoter regions

9

genomic imprinting

different genes are epigentically silenced in eggs and sperm

in sperm, all maternal imprints are erased and rewritten

in eggs, all paternal imprints are erased and rewritten

10

imprinting and cancer

if both alleles are methylated, then IGF2 promotes cell growth and cancer

11

five modifications of the histone tail

acetylation, methylation, ubiquination, sumoylation, and phosphorylation

12

describe the process of chromatin immunoprecipitation

13

H3K4me3

leads to gene activation, associated with euchromatin

14

H3K9me3

leads to gene silencing and associated with heterochromatin

15

HP1

chromodomain of this protein binds H3K9me3 and spreads the methylation and thus silences the genes

16

stem cell histone code

often bivalent, with some active markers and some repressive markers

allows cells to be poised for expression or silencing so they can differentiate

17

FISH

fluorescence in situ hybridization

18

karyotype

the number and appearance of chromosomes in the nucleus of a eukaryotic cell

19

nuclear localization of chromosome 18 and 19

chromosome 19 - gene rich, high density of CpG islands, DNA is mostly early replicating, high levels of hyperacetylated histone H4

chromosome 18 - relatively gene poor, low CpG island density, high  proportion of late replicating DNA, low levels of hyperacetylated H4

if the two chromosomes are translocated, the gene poor region of 18 will still go to the periphery regardless

20

Barr Bidy

the silenced X chromosome in females

21

Xist

non-coding RNA involved in X chromosome silencing, made at the X inactivation center, coats the chromosomes and brings in modifying enzymes that condense the chromosomes

22

Tsix

antisense RNA to Xist, prvents both X chromosomes from being silenced

balance between Xist and Tsix