epigenetics and gene expression

Question 1

in eukaryotic organisms, give one process controlled by epigenetics ?

Answer 1

• gene expression in protein synthesis
• so when a protein is made

Question 2

what is meant by epigenetics ?

Answer 2

• the heritable change in gene function (preventing gene expression)
• without changing the DNA sequence

Question 3

what are heritable changes in gene function caused by ?

Answer 3

• changes in the environment

Question 4

what can heritable changes inhibit ?

Answer 4

• they can inhibit transcription

Question 5

what kind of environmental factors can cause heritable changes ?

Answer 5

• diet
• stress
• toxins

Question 6

what can the environmental factors do to the DNA to cause heritable changes ?

Answer 6

• they can add or remove epigenetic chemical tags to the DNA
• and this can control gene expression in eukaryotes

Question 7

what is the single layer of chemical tags on the DNA called ?

Answer 7

• epigenome

Question 8

what does the epigenome impact ?

Answer 8

• this impacts the shape of the DNA-histone complex
• and whether the DNA is tightly wound so won’t be expressed or unwound so it will be expressed

Question 9

what happens if the histone is tightly wound around the DNA ?

Answer 9

• DNA will not be expressed
• transcription factors cannot bind
  -so epigenome, which is due to changes in the environment, can inhibit transcription

Question 10

will the DNA be expressed if the histone is unwound ?

Answer 10

• yes
• it will be expressed
• as genes are accessible to be transcribed

Question 11

what are the 3 types of chemical tags ?

Answer 11

• methylation of DNA
• acetylation of histone proteins

Question 12

what is meant by methylation of DNA ?

Answer 12

• when methyl groups are added to the DNA

Question 13

what does increased methylation of DNA do ?

Answer 13

• it inhibits transcription

Question 14

where do the methyl groups attatch to ?

Answer 14

the cytosine base

Question 15

how does increased methylation inhibit transcription ?

Answer 15

• by binding onto cytosine bases
• it prevents transcriptional factors from binding
• and attracts proteins that condense the DNA -histone complex
• so it prevents a section of DNA from being transcribed

Question 16

how does methylation make the DNA more compact ?

Answer 16

• methyl groups are positively charges
• DNA is negatively charged
• so the strong attraction between opposite charges causes them to become compact

Question 17

what does decreased acetylation of associated histone proteins on DNA do ?

Answer 17

• it inhibits transcription

Question 18

what occurs when the acetyl groups are removed from the DNA ?

Answer 18

• the histones become more positive and are attracted more to the phosphate group on the DNA
• this makes the DNA and histones more strongly associated and hard for transcription factors to bind

Question 19

where are acetyl groups binded to ?

Answer 19

• the histones

Question 20

what does increased acetylation cause ?

Answer 20

• histones to become loosely packed
• so transcription factors can bind to the DNA and genes can be expressed

Question 21

what is the term given when the DNA is tightly coiled ?

Answer 21

• heterochromatin

Question 22

what is the term given when the DNA is loosely coiled ?

Answer 22

• euchromatin

Question 23

what is heterochromatin caused by ?

Answer 23

• increased methylation
• decreased acetylation

Question 24

what is euchromatin caused by ?

Answer 24

• decreased methylation
• increased acetylation

Question 25

what are tumour suppressor genes ?

Answer 25

- genes that produce proteins to slow down cell division - and to cause cell death if DNA copying errors are detected

Question 26

what occurs if a mutation results in a tumour suppressor gene not producing the proteins to carry out its function ?

Answer 26

- the cell division could continue - mutated cells would not be identified and destroyed

Question 27

what are the 2 known mutated tumour suppressor genes that are linked to breast cancer ?

Answer 27

- BRCA1 - BRCA2

Question 28

what can methylation cause a gene to do ?

Answer 28

- can cause a gene to be turned off or on

Question 29

what can happen to tumour suppressor genes in terms of methylation ?

Answer 29

they could become hypermethylated

Question 30

what does the hypermethylation of tumour suppressor genes result in ?

Answer 30

- an increased number of methyl groups become attatched to it - coiling it up - resulting in genes being inactivated and become turned off - so you can get uncontrolled cell division

Question 31

what can occur in oncogenes in terms of methylation ?

Answer 31

- they can become hypomethylated

Question 32

what occurs when oncogenes are hypomethylated ?

Answer 32

- it reduces the number of methyl groups attached to it - causing it to unwravel - which results in the gene being permanently switched on - oncogenes create proteins which trigger mitosis to occur - so this will result in uncontrolled mitosis and cell division