Epigenetics

Question 1

euchromatin vs. heterochromatin

Answer 1

euchromatin - electron poor, active

heterochromatin - electron dense, compacted, inactive

Question 2

five currently known mechanisms of epigenetics

Answer 2

trithorax-group and polycomb-group proteins

DNA methylation

histone modifications

nuclear comparmentalization

non-coding RNA

Question 3

histone H1

Answer 3

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

Question 4

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

Answer 4

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

Question 5

DNA methylation

Answer 5

the addition of a methyl group to the DNA base cytosine

tends to occur on CpG regions

Question 6

Dnmt3a and 3b

Answer 6

carry out denovo methylation

3b is mostly near centromeres

3a is mostly for areas further from the centromeres

Question 7

Dnmt 1

Answer 7

maintenance methyltransferase

Question 8

CpG Islands

Answer 8

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

Question 9

genomic imprinting

Answer 9

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

Question 10

imprinting and cancer

Answer 10

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

Question 11

five modifications of the histone tail

Answer 11

acetylation, methylation, ubiquination, sumoylation, and phosphorylation

Question 12

describe the process of chromatin immunoprecipitation

Answer 12

Question 13

H3K4me3

Answer 13

leads to gene activation, associated with euchromatin

Question 14

H3K9me3

Answer 14

leads to gene silencing and associated with heterochromatin

Question 15

HP1

Answer 15

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

Question 16

stem cell histone code

Answer 16

often bivalent, with some active markers and some repressive markers

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

Question 17

FISH

Answer 17

fluorescence in situ hybridization

Question 18

karyotype

Answer 18

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

Question 19

nuclear localization of chromosome 18 and 19

Answer 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

Question 20

Barr Bidy

Answer 20

the silenced X chromosome in females

Question 21

Xist

Answer 21

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

Question 22

Tsix

Answer 22

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

balance between Xist and Tsix