Chapter 27 Epigenetics

Question 1

Epigenetics

Answer 1

Any potentially stable and heritable change in gene expression that occurs without a change in DNA sequence
OR
phenomena in which genetically identical cells or organisms express their genomes differently, causing phenotypic differences.

Question 2

prion

Answer 2

proteinaceous infectious agent that behaves as an inheritable trait, although it contains no nucleic acid

Examples: PrPSc in sheep, PSI in yeast

Question 3

DNA Methylation function

Answer 3

Generally a repressive mark:
Reduces DNA-binding of many proteins
Condenses chromatin structure
Binding site for methyl binding proteins

Question 4

Transposons

Answer 4

• Fragments of DNA that can insert into new chromosomal locations
• Some copy themselves and increase in number within the genome
• Responsible for large scale chromosome rearrangements and single-gene mutagenic events

Question 5

Vernalization

Answer 5

quantitative
perceived by dividing cells (SAM)
not graft transmissible
mitotically stable
reversible --> reset at meiosis
epigenetic basis

Question 6

Transposons

Answer 6

• Fragments of DNA that can insert into new chromosomal locations
• Some copy themselves and increase in number within the genome
• Responsible for large scale chromosome rearrangements and single-gene mutagenic events
–> inactive or unstable alleles

Question 7

Transposon controlle

Answer 7

DNA methylation
histone modification
siRNA production

Question 8

Amphipathic Helix-loop-Helix (HLH) motif

Answer 8

Amphipathic alpha helix with one hydrophobic and one charged surface
Connecting loop: 12 – 28 aa
HLH motif enables dimerization
Basic regions makes contact to DNA (bHLH protein)

Question 9

Helix-turn-helix

Answer 9

Two α-helices that form a site that binds to DNA, one fitting into the major groove of DNA and the other lying across it.
C-terminal alpha helix contacts major groove, middle helix lies across, N-terminal arm in minor groove
Closely related: Homeodomain TFs

Question 10

Histone acetylation

Answer 10

Newly synthesized histones are acetylated at specific sites
Deacetylation occurs after incorporation into nucleosomes
is associated with activation of gene expression
can occur locally or globally (e.g. on sex chromosomes)
HATs: Histon acetyltransferases
HDACs: Histon deacetylases
Group A: acts on chromatin
Group B: acts on newly synthesized histones (cytosolic)

Question 11

Histone and DNA methylatio

Answer 11

Acetylation of histones activates chromatin; methylation of DNA and specific sites on histones inactivates chromatin.
Methylation of histones and DNA are connected in a reinforcing cycle
H3K9 methylation recruits protein HP1 which in turn targets DNA methyltransferase (DNMT)
Methylated CpG islands in turn recruit Histone methylation transferase and HDAC complexes

Question 12

Histone Phosphorylation

Answer 12

All histones can be phosphorylated
Histone phosphorylation associated with:
transcription
repair
chromosome condensation
cell-cycle progression