Chapter 9: 9.1 Eukaryotic Epigenetic Regulation

Question 1

How is accessing the genes in eukaryotes a way that expression is regulated?

Answer 1

Genes are wrapped around in histones

Question 2

What is regulation by accessing the genes around histones known as?

Answer 2

Epigenetics

Question 3

Histone tails

Answer 3

Strings of protruding amino acids

Question 4

How can histone tails be modified?

Answer 4

Acetyl groups or Methyl groups can be added

Question 5

What does the acetyl/methyl groups added to histone tails do to the DNA wrapped around it?

Answer 5

Affects how tightly DNA is wrapped around it

Question 6

Where do the acetyl and methyl groups occur on the histone tails?

Answer 6

Usually occur on lysine residues

Question 7

Epigenetic modifications make up the…

Answer 7

Histone code

Question 8

True or False:

Modifications that make up the histone code represses transcription

Answer 8

Partially true; Can either enhance or repress transcription

Question 9

HATs

Answer 9

Histone acetyltransferases
* Adds acetyl groups to histones

Question 10

Acetylation

Answer 10

Usually enhances transcription
* Loosens the DNA-histone binding
* Makes DNA more accessible to transcriptional machinery

Question 11

Methylation

Answer 11

Either enhances or represses transcription
* Me enhances
* Me3 represses

Question 12

True or False:

Epigenetic modification only occurs to the histone tails

Answer 12

False, they can also occur to the DNA itself

Question 13

What is the most common modification to DNA itself?

Answer 13

Addition of methyl group to cytosine nucleotides

Question 14

Where does cytosine methylation occur on the DNA?

Answer 14

CpG islands
* Clusters of adjacent CG nucleotides located in/near the promoter of a gene

Question 15

How do CpG methylation states change? What is its purpose

Answer 15

Change in response to environmental conditions
* Mechanism for turning on/off genes

Question 16

X-chromosome inactivation

Answer 16

A form of epigenetic control
* An entire chromosome is inactivated

Question 17

Dosage compensation

Answer 17

Inactivation of one X chromosomes in females to avoid over-expression of genes

Question 18

Why does dosage compensation occur?

Answer 18

Females have two X-chromosomes (1 maternal and 1 paternal)
* Inactivate one to prevent over expression

Question 19

True or False:

There is a specific X chromosome that is inactivated

Answer 19

False, which X chromosome is inactivated occurs randomly

Question 20

When does X chromosome inactivation occur?

Answer 20

Occurs randomly after the first few rounds of embryonic cell division

Question 21

What does the mechanism of X chromosome inactivation involve?

Answer 21

A non-coding RNA
* Called Xist

Question 22

How does Xist work?

Answer 22

Coats the X chromosome and recruits factors that promote:
* DNA methylation
* Histone modification
* Other changes that repress trancription