Epigenetics

Question 1

Epigenetics is:

Answer 1

• Heritable changes in gene function that occur without a change in the DNA sequence

Question 2

Three ways to epigenetically alter gene expression:

Answer 2

1. DNA methylation
2. histone modification
3. noncoding RNA

Question 3

DNA methylation:

Answer 3

• hypermethylation blocks transcription
• occurs before the promoter
  
  • specifically, hypermethylation of CpG islands

Question 4

CpG Islands:

Answer 4

• repeating CG base pairs (1/10bp)
• usually are in the promoter of a gene
• C can be methylated to block gene expression

Question 5

dMTase:

(demethylase)

Answer 5

• eraser enzyme that removes methylated groups from DNA.

Question 6

DNMT 3a/3b:

(DNA methyltransferase 3a/3b)

Answer 6

• writer enzyme that adds methyl groups to DNA (de novo methylation).

Question 7

DNMT 1:

(DNA methyltransferase 1)

Answer 7

• enzyme important for methylation maintenance.

Question 8

MeCP2:

Answer 8

• binds to a methylated DNA and blocks transcription of a gene that should be silenced.
• If a mutation in MeCP2, MeCP2 cannot bind to a specific DNA methylation, silenced gene is expressed.

Question 9

Imprinted genes play vital roles in:

Answer 9

• embryonic growth, neonatal behavior, tissue and developmental stages.

Question 10

HATs:

Answer 10

• acetylate histone tails causing unwinding of chromatin, making it more relaxed and accessible to transcription.
• transcription occurs.

Question 11

HDACs:

Answer 11

• Deacteylate histone tails
• results in a compact chromatin structure and silencing of transcription.

Question 12

Euchromatin methylation/acetylation pattern:

Answer 12

• high histone acetylation, low DNA methylation

Question 13

Heterochromatin methylation/acetylation pattern:

Answer 13

• low histone acetylation, dense DNA methylation,

Question 14

Xist:

Answer 14

Xist DEACTIVATES X CHROMOSOME

• non-coding RNA that hyperacetylates and inactivates the X chromosome

Question 15

Tsix:

Answer 15

Tsix ACTIVATES X CHROMOSOME

• a noncoding RNA that inactivates Xist
• is anti-sense to Xist
• X chromosome becomes ACTIVE

Question 16

Two syndromes caused by mutations/deletions of parental imprinting:

Answer 16

1. Prader–Willi Syndrome
2. Angelman Syndrome

Question 17

Agouti gene:

Answer 17

METHYL RICH DIET DURING PREGNANCY

• methylated (rich diet):
  
  • gene blocked from being transcribed
  • brown and healthy mice
• not methylated (poor diet):
  
  • gene is continuously active
  • blonde and obese mice

Question 18

Two Methods to study changes in epigenome:

Answer 18

• Bisulfite conversion DNA (C → T)
• Methylation-sensitive restriction enzymes