chromatin

Question 1

histone acetyltransferase

Answer 1

adds acetyl groups to lysine residues

Question 2

histone deacetylase

Answer 2

removes acetyl groups

Question 3

histone methyltransferase

Answer 3

adds methyl groups to lysine and arginine residues

Question 4

histone demethylase

Answer 4

removes methyl groups

Question 5

code writer

Answer 5

makes modifications which regulate gene transcription

e.g. histone methyltransferase, histone acetyltransferase etc.

Question 6

code reader

Answer 6

recognises modifications which regulate gene transcription

e.g. activators, repressors

Question 7

methylation of core histones at H3K27, H3K9 creates binding sites for _________ containing a ___________

Answer 7

repressors

chromodomain

Question 8

methylation of core histones at H3K4 creates binding sites for _________ containing a _____________

Answer 8

activators

PHD zinc finger domain

Question 9

acetylation of core histones creates binding sites for ________ containing a _____________

Answer 9

activators

bromodomain

Question 10

how do activators work?

Answer 10

• selective nucleosome remodelling by relaxing chromatin
• selective histone removal to reveal DNA sequences
• selective histone replacement (allows greater access to nucleosomal DNA)
• selective histone modification
  PROMOTES rna polymerase II recruitment

Question 11

how do repressors work?

Answer 11

• compete with activators for binding to same regulatory dna sequence
• mask activation surface
• blocks assembly of general transcription factors
• recruits histone deacetylases and histone methyltransferases
• recruits chromatin remodelling complexes - tightens chromatin

Question 12

MeCP2

Answer 12

proteins which bind to CpG dinucleotides + interact with histone deacetylases & histone methyltransferases to transform acetylated nucleosomes into methylated nucleosomes

Question 13

what is a Barr Body?

Answer 13

transcriptionally silent, highly condensed X chromosome at the periphery of the nucleus of female somatic cells

Question 14

Agouti mouse

Answer 14

dominant mutant of agouti gene resulting in constitutively high expression of agouti protein
phenotype = yellow fur + obesity
contains insertion of IAP element which is sensitive to methylation. high levels of methyl donors in maternal diet causes transcriptional silencing of IAP element + represses agouti mutant gene in progeny.

Question 15

how is the X chromosome randomly silenced in female somatic cells?

Answer 15

Xist (non-coding RNA) is synthesised from X inactivation centre
Xist binds to X chromosome + promotes chromatin condensation
by recruiting polycomb group, histone methyltransferases, histone deacetylases + DNA methyltransferases