3.14 Epigentics

Question 1

How can an organism’s internal and external environment influence gene expression patterns?

Answer 1

levels of regulatory proteins or transcription factors can be affected by environmental stimuli such as light, and chemicals such as drugs and hormones

Question 2

What is epigenetics?

Answer 2

the control of gene expression by factors other than an individual’s DNA sequence

Question 3

What does epigentics involve?

Answer 3

the switching on and switching off of genes, but without changing the actual genetic code

Question 4

What is nuclear DNA wrapped around and what does this form?

Answer 4

histones to form chromatin

Question 5

How can chromatin be chemically modified to alter gene expression?

Answer 5

• methylation of DNA (adding -CH3 groups)
• histone modification via acetylation

Question 6

What is an epigenome?

Answer 6

consists of all the chemical modifications that influence gene expression (called chemical markers or chemical tags)

Question 7

What does it mean that epigenetic modification is independent?

Answer 7

DNA methylation or histone modification in one area is not linked to modification in another

Question 8

What does DNA methylation do?

Answer 8

• methyl groups are usually added to cytosine bases
• it prevents transcription of the affected gene by preventing RNA polyermase from binding
• the gene is inactivated

Question 9

What does acetylation of histones do?

Answer 9

• acetyl (and sometimes methyl) groups are added to histones
• this affects how tightly DNA is wrapped around the histone
• when DNA is wrapped tightly, RNA polyermase and transcription factors cannot bind to the DNA
• this means they cannot be transcribed and therefore the gene is inactivated
• acetylation of histones causes DNA to be less tightly wrapped, allowing RNA polyermase to bind more easily and for gene expression to occur (the gene is activated)

Question 10

The epigonome can be during cell division. How?

Answer 10

epigentic changes (methylation of DNA and modification of histones) are copied during DNA replication and so can be passed on to daughter cells