3.4.4 - Epigenetics

Question 1

What Is Epigenetics?
(4 Points)

Answer 1

~ An organisms internal or external environment influences gene expression.

~ Is the control of gene expression by factors other than an individuals DNA sequence.

~ It involves the switching on and off of genes, without changing the actual genetic code or base sequence of DNA.

~ Levels regulatory proteins or transcription factors can be affected in response to environmental stimuli such as light.

Question 2

Describe Nuclear DNA In Eukaryotic Cells
(2 Points)

Answer 2

~ Nuclear DNA is wrapped around proteins called histones to form chromatin.

~ Chromatin can then be chemically modified to alter gene expression.

Question 3

How Can Chromatin Be Chemically Modified To Alter Gene Expression?
(2 Points)

Answer 3

~ Methylation of DNA -> chemical addition of CH3 groups.

~ Histone modification via acetylation of amino acid tails.

Question 4

Describe The Epigenome

Answer 4

Modifications are called epigenetic tags, collectively all the epigenetic tags is called the epigenome.

Question 5

What Environmental Factors Cause The Epigenome To Undergo Changes?
(2 Points)

Answer 5

~ Smoking, stress, exercise and diet -> Cause epigenetic changes.

~ Internal signaling from bodies own cells -> Cause modifications to occur.

Question 6

Describe The Process Of DNA Methylation
(4 Points)

Answer 6

~ A methyl group is added to DNA to change the activity of a gene.

~ The methyl group is always added to the CpG site, where the cytosine and the guanine bases are next to each other.

~ Suppresses the transcription of the affected gene by inhibiting the binding of transcription factors and enzymes needed for transcription (RNA polymerase).

~ Gene is repressed.

Question 7

What Are Histones?

Answer 7

Proteins that DNA wraps around to form chromatin.

Question 8

Describe Chromatin
(2 Points)

Answer 8

~ Can be highly condensed or less condensed.

~ How condensed it is affects the accessibility of the DNA and whether or not the proteins and enzymes needed for transcription can bind to it.

Question 9

What Happens When Histones Are Acetylated?
(4 Points)

Answer 9

~ Acetyl groups are added to the histones.

~ Chromatin is less condensed.

~ Proteins involved in transcription can bind to the DNA.

~ Allowing genes to be transcribed (Activated).

Question 10

What Happens When Acetyl Groups Are Removed From The Histones?
(3 Points)

Answer 10

~ Chromatin becomes highly condensed.

~ Genes in the DNA cannot be transcribed because RNA polymerase cannot bind to the them.

~ Genes are repressed.