8A 6. Epigenetic control of gene expression

Question 1

what can epigenetic control determine

Answer 1

wether or not a gene is expressed (transcribed and translated)

Question 2

how does epigenetic control work

Answer 2

through the attachment or removal of a chemical group (known as epigenetic marks)
to or from DNA or histone proteins

Question 3

what don’t epigenetic markers alter

Answer 3

the base sequence of DNA

Question 4

what do epigentic markers alter

Answer 4

how easy it is for the enzymes and other proteins needed for transcription to interact with and transcribe DNA

Question 5

what can cause epigentic changes to gene expression

Answer 5

response to changes in the environment e.g. pollution and availability of food
(epigenetics also plays a role in lots of normal cellular processes)

Question 6

can epigenetic changes be inherited by offspring

Answer 6

yes

Question 7

how are epigenetic changes inherited by offspring

Answer 7

1. organisms inherit DNA base sequence from parents
2. most epigenetic markers on DNA removed between generations. some escape removal process and passed to offspring.
3. expression of some genes can therefore be affected by environmental changes that affected parent or grandparents
   e. g. epigenetic changes is some plants response to drought have been shown to be passed on to later generations

Question 8

increased methylation of DNA causes gene to be switched on or off?

Answer 8

switched off

Question 9

methylation of DNA explained in 2 points

Answer 9

1. methyl group attaches to DNA coding for a gene
2. increased methylation changes DNA structure so transcriptional factors cant interact with gene- it is therefore switched off/ not expressed

Question 10

Decreased Acetylation of Histones causes genes to be switched on or switched off?

Answer 10

switched off

Question 11

e.g. of transcriptional markers causing genes to switch off

Answer 11

increased methylation of DNA

decreased acetylation of histones

Question 12

what are histones

Answer 12

proteins DNA wraps around to form chromatin, which makes up chromosomes

Question 13

Acetylation of histones explained in 3 points

Answer 13

1. Histones can be epigenetically modifies by addition or removal of acetyl groups
2. histones acetylated = chromatin less condensed. transcriptional factors can access DNA = DNA can be transcribed.
3. acetyl groups removed from histones = chromatin highly condensed. transcriptional factors cant access DNA = DNA cant be transcribed.

Question 14

what enzymes are responsible for removing the acetyl groups

Answer 14

Histone deacetylase (HDAC)

Question 15

where does methyl group attach on the DNA

Answer 15

always attaches to CpG site where cytosine and guanine base next to each other in DNA (linked by phosphodiester bond)

Question 16

Epigenetics plays a role in the development of diseases. 2 examples

Answer 16

1. Cancer

2. Fragile- X syndrome

Question 17

how does epigenetics play a role in the development of cancer

Answer 17

1abnormal methylation of tumour supressor genes and oncogenes can cause

Question 18

how does epigenetic play a role in the development of Fragile x syndrome

Answer 18

mutation results in

Question 19

what is Fragile x syndrome caused by

Answer 19

heritable duplication mutation in a gene on x chromosome called FMR1

Question 20

fragile x syndrome - what does mutation result in

Answer 20

short DNA sequence CGG being repeated more times than usual

lots more CpG sites = increased methylation of gene which switches it off

Question 21

fragile x syndrome - what happens as a result of gene being switched off

Answer 21

protein not produced.

lack of protein causes symptom of disease.

Question 22

Symptoms of Fragile-X syndrome

Answer 22

learning and behavioural difficulties

characteristic physical features

Question 23

how do drugs treat diseases caused by epigenetic changes

Answer 23

counteract the epigenetic changes that cause the disease (epigenetic changes are reversible)

Question 24

ways in which drugs can counteract epigenetic changes that cause disease

Answer 24

increased methylation can lead to a gene being switched off - drugs that stop DNA methylation can be used to treat diseases caused this way
decreased acetylation of histones can lead to gene being switched off - HDAC inhibitor drugs can be used to treat diseases caused this way

Question 25

example of a drug that that stops DNA methylation

Answer 25

azacitidine (used in chemotherapy for types of cancer caused by increased methylation of tumour suppressor genes)

Question 26

e.g. of HDAC inhibitor drug

Answer 26

romidepsin

Question 27

how do HDAC inhibitor drugs work

Answer 27

inhibit activity of histone deacetylace (HDAC) enzymes which remove acetyl groups from histones.
genes remain acetylated and proteins they code for can be transcribed.

Question 28

what is the problem with developing drugs to counteract epigenetic changes

Answer 28

changes take place in lots of cells important to make sure drugs specific as possible.

Question 29

example of over coming problems in developing drugs to counteract epigenetic changes

Answer 29

drugs used in cancer therapies can be designed to only target dividing cells
to avoid damage to normal body cells.