35. HISTONE MODIFICATIONS Flashcards
1
Q
- What are 2 types of Histone Modification?
A
- Histone Acetylation
- Histone Deacetylation
2
Q
- What implements Histone Acetylation?
A
- the Histone Acetylation Enzymes
3
Q
- What do the Histone Acetylation Enzymes promote?
A
- they promote the initiation of transcription
- they do this by remodelling the chromatin structure
- they also recruit the transcription machinery
4
Q
- What can be said about the N-terminal of each histone molecule?
A
- these molecules are found in a nucleosome
- this N-terminal protrudes outward
5
Q
- What do Acetyl groups (-COCH₃) attach to?
A
- they attach to lysines
- these are positively charged
- they are found in the histone tails
6
Q
- What happens when the Lysines are Acetylated?
A
- the lysine is attached to the Acetyl group
- the lysine positive charges are neutralised
- the histone tails do not bind to the neighbouring
nucleosomes
7
Q
- What does Histone Acetylation result in?
A
- the Chromatin structure is looser
- this activates transcription
8
Q
- What implements Histone Deacetylation?
A
- Histone Deacetylases
- HDACs
9
Q
- What is removed during Histone Deacetylation?
A
- the Acetyl groups are removed from the lysine tail
- this restores the positive histone charge
- the histones will bind to their neighbouring
nucleosomes
10
Q
- What does Histone Deacetylation result in?
A
- the chromatin structure becomes more packed
- it is now inactive
- Transcription is inactivated
11
Q
- What is added during Histone Methylation?
A
- Methyl groups are added (-CH₃) in an amino acid to the
histone - these groups ate non-polar
- they are either added to Lysine or Arginine
12
Q
- What does Histone Methylation result?
A
- the Chromatin is condensed
- gene expression is inactivated
13
Q
- What does the methylation of some lysine and arginine residues of Histones result in?
A
- Transcriptional Activation
14
Q
- What is Phosphorylation?
A
- a phosphate group is added to an amino acid
- this amino acid is found to the methylated amino acid
15
Q
- What does Phosphorylation result in?
A
- it results in the chromatin decondensing
- this activates transcription
16
Q
- What is DNA Methylation?
A
- this is the addition of Methyl groups (CH₃) to specific
bases - the base is usually Cytosine
- this leads to reduced transcription
17
Q
- What does DNA Methylation result in?
A
- it results in the long term inactivation of genes
- these genes are used in cellular Differentiation
18
Q
- Where do genes experience more Methylation?
A
- cells that do not express methylation
19
Q
- When does Genomic imprinting occur?
A
- it occurs during the formation of gametes
20
Q
- What does Genomic Imprinting result in?
A
- it results in the silencing of one of the parental alleles
- this allele is not expressed in the phenotype
21
Q
- How do we silence an allele?
A
- we use Methylation
- we add a Methyl group to it
- we usually add the Methyl to the Cytosine nucleotides
22
Q
- How many alleles of an imprinted gene does a zygote express?
A
- one allele
- either the maternal or the paternal
- this one allele is expressed in every cell of the
organism
23
Q
- What percentage of mammalian DNA is affected by DNA methylation?
A
- 1% of mammalian genes
