20.4 epigenetic control of gene expression

Question 1

define epigenetics

Answer 1

process by which environmental factors can cause heritable changes in gene function without changing the base sequence of DNA

Question 2

define epigenome

Answer 2

chemical tags that determine the shape of the chromatin

Question 3

which bit of the contents of the nucleolus is fixed?

Answer 3

DNA

Question 4

which bit of the contents of the nucleolus is flexible

Answer 4

epigenome

Question 5

what do the epigenetic tags respond to?

Answer 5

signals in the environment e.g. diet, stress and toxins

Question 6

how does the epigenome adjust the chromatin?

Answer 6

• makes some chromatin tightly wrapped so are inaccessible to transcriptional factors
• makes some chromatin loosely packed so are easily accessible to transcriptional factors

Question 7

what are the 2 ways in which signals from the environment can caused condensation of the chromatin?

Answer 7

• decreased acetylation of histones

- increased methylation of DNA

Question 8

how does decreased acetylation of histones cause the gene to become inaccessible?

Answer 8

• increases the positive charges on the histones
• increases the attraction to the phosphate group on the DNA
• gene switched off

Question 9

what are the 2 ways in which increased methylation inhibits transcription of genes?

Answer 9

• preventing the binding of transcriptional factors to the DNA
• induced deacetylation, making the DNA inaccessible to transcriptional factors

Question 10

acetylation definition

Answer 10

process where an acetyl group is transferred to a molecule

Question 11

deacetylation definition

Answer 11

process where an acetyl group is transferred from a molecule

Question 12

methylation definition

Answer 12

process where a methyl group is transferred to a molecule

Question 13

demethylation definition

Answer 13

process where a methyl group is transferred from a molecule

Question 14

what is the increased methylation of DNA?

Answer 14

methyl group is added to the cytosine bases of DNA

Question 15

what are 2 ways in which cancer can be caused?

Answer 15

• activation of a normally inactive gene

- inactivation of a normally active gene

Question 16

describe the process in which RNA interference effects gene expression

Answer 16

1. double stranded RNA is broken up by an enzyme into siRNA
2. 1 of the 2 strands of siRNA combines with an enzyme
3. siRNA pairs with complementary bases on mRNA strand
4. enzyme cuts the mRNA into smaller sections