35. HISTONE MODIFICATIONS

Question 1

1. What are 2 types of Histone Modification?

Answer 1

1. Histone Acetylation
2. Histone Deacetylation

Question 2

2. What implements Histone Acetylation?

Answer 2

• the Histone Acetylation Enzymes

Question 3

3. What do the Histone Acetylation Enzymes promote?

Answer 3

• they promote the initiation of transcription
• they do this by remodelling the chromatin structure
• they also recruit the transcription machinery

Question 4

4. What can be said about the N-terminal of each histone molecule?

Answer 4

• these molecules are found in a nucleosome
• this N-terminal protrudes outward

Question 5

5. What do Acetyl groups (-COCH₃) attach to?

Answer 5

• they attach to lysines
• these are positively charged
• they are found in the histone tails

Question 6

6. What happens when the Lysines are Acetylated?

Answer 6

• the lysine is attached to the Acetyl group
• the lysine positive charges are neutralised
• the histone tails do not bind to the neighbouring
  nucleosomes

Question 7

7. What does Histone Acetylation result in?

Answer 7

• the Chromatin structure is looser
• this activates transcription

Question 8

8. What implements Histone Deacetylation?

Answer 8

• Histone Deacetylases
• HDACs

Question 9

9. What is removed during Histone Deacetylation?

Answer 9

• the Acetyl groups are removed from the lysine tail
• this restores the positive histone charge
• the histones will bind to their neighbouring
  nucleosomes

Question 10

10. What does Histone Deacetylation result in?

Answer 10

• the chromatin structure becomes more packed
• it is now inactive
• Transcription is inactivated

Question 11

11. What is added during Histone Methylation?

Answer 11

• 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

Question 12

12. What does Histone Methylation result?

Answer 12

• the Chromatin is condensed
• gene expression is inactivated

Question 13

13. What does the methylation of some lysine and arginine residues of Histones result in?

Answer 13

• Transcriptional Activation

Question 14

14. What is Phosphorylation?

Answer 14

• a phosphate group is added to an amino acid
• this amino acid is found to the methylated amino acid

Question 15

15. What does Phosphorylation result in?

Answer 15

• it results in the chromatin decondensing
• this activates transcription

Question 16

16. What is DNA Methylation?

Answer 16

• this is the addition of Methyl groups (CH₃) to specific
  bases
• the base is usually Cytosine
• this leads to reduced transcription

Question 17

17. What does DNA Methylation result in?

Answer 17

• it results in the long term inactivation of genes
• these genes are used in cellular Differentiation

Question 18

18. Where do genes experience more Methylation?

Answer 18

• cells that do not express methylation

Question 19

19. When does Genomic imprinting occur?

Answer 19

• it occurs during the formation of gametes

Question 20

20. What does Genomic Imprinting result in?

Answer 20

• it results in the silencing of one of the parental alleles
• this allele is not expressed in the phenotype

Question 21

21. How do we silence an allele?

Answer 21

• we use Methylation
• we add a Methyl group to it
• we usually add the Methyl to the Cytosine nucleotides

Question 22

22. How many alleles of an imprinted gene does a zygote express?

Answer 22

• one allele
• either the maternal or the paternal
• this one allele is expressed in every cell of the
  organism

Question 23

23. What percentage of mammalian DNA is affected by DNA methylation?

Answer 23

• 1% of mammalian genes