epigenetic control of gene expression

Question 1

epigenetic changes

Answer 1

changes in the gene expression, that are not caused by a change in the gene itself
(there has been no change in DNA base sequence of the gene, but in some cells the gene is expressed and in others, it is not)

Question 2

causes of epigenetic changes

Answer 2

1) increased methylation of the DNA

2) decreased acetylation of associated histones

Question 3

methylation of DNA

Answer 3

• adding a methyl group -CH3

- to cytosine bases adjacent to guanine bases

Question 4

CpG site

Answer 4

regions of DNA where a cytosine nucleotide is followed by a guanine nucleotide in the linear sequence of bases

Question 5

effect of increasing methylation

Answer 5

• prevents the binding of transcription factors and RNA polymerases
• which prevents gene expression

Question 6

transcription factors

Answer 6

proteins that controls the rate of transcription of genetic information from DNA to mRNA, by binding to a specific DNA sequence

Question 7

what causes methylation and acetylation

Answer 7

environmental factors, such as:

• diet
• smoking
• exercise
• stress
• working habits

Question 8

acetylation of associated histones

Answer 8

• histones are chemically modified by the addition of an acetyl group

Question 9

effect of decreasing acetylation of associated histones

Answer 9

• addition of acetyl groups to histones makes the DNA more accessible for transcription
• a decrease would lead to less gene expression

Question 10

histones

Answer 10

protein structures which DNA is packaged and coiled around

Question 11

promoters

Answer 11

regions close to the start of a gene where RNA will bind to in order to initiate transcription of said gene

Question 12

hypermethylation of tumour suppressor genes

Answer 12

• excess of methyl groups are added to promotors for tumour suppressor genes
• gene expression is prevented

Question 13

hypomethylation of proto-oncogenes

Answer 13

• lack of addition of methyl groups to promotors of proto-oncogenes
• this will lead them to becoming oncogenes
• genes are overexpressed

Question 14

control of cell cycle

Answer 14

• proto-oncogenes: lead to cell devision

- tumour supressor genes: stop/slow down cell division

Question 15

epigenetic therapies for cancer treatment

Answer 15

• enzymes responsible for methylation of DNA (DNA methyltransferases) have been identified
• there are drugs that inhibit DNAMTi
• silent tumour supressor genes are reactivated

Question 16

how do certain drugs affect DNAMTi

Answer 16

• the inhibitors bind to the enzyme permenantly
• making the active site unavailable to bind to promotors of tmg
• this reduces enzyme activity or number of active enzymes
• less methylation occurs
• normal pattern of DNA methylation and gene expression restored