Chromatin Structure

Question 1

The proteins that bind to DNA to form eukaryotic chromosomes are traditionally divided into 2 general classes:

Answer 1

Histones and nonhistone Chromosomal proteins.

Question 2

Histones are present in ________ quantities, and their total mass in chromosomes _____________.

Answer 2

• enormous ( more than 60 million molecules of several different types in each cell)
• Is about equal to that of the DNA itself!

Question 3

The complex of both classes of protein with nuclear DNA is called ________.

Answer 3

Chromatin.

Question 4

Histones are responsible for the first and fundamental level of chromatin packing _______.

Answer 4

The nucleosome

Question 5

The string of DNA, and each bead is a ____________, which consists of DNA wound around a core of proteins formed from ___________.

Answer 5

• Nucleosome core particle

- Histones

Question 6

An individual nucleosome core particle consists of a complex of ____ histone proteins. What are they and what else?

Answer 6

• 8
• Two molecules each of histones H2A, H2B, H3, and H4. And a stretch of double stranded DNA, 147 nucleotide pairs long, which winds around the histone octamer.

Question 7

30 nm thick?

Answer 7

-Chromatin isolated directly form an inter-phase nucleus appears in the electron microscope as a chromatin fiber about 30-nm thick.

Question 8

What is a Chromatin remodeling complex?

Answer 8

Its an enzyme (typically multisubunit) that uses the energy of ATP hydrolysis to alter the arrangement of nucleosomes in eukaryotic chromosomes, changing the accessibility of the underlying DNA to other proteins, including those involved in transcription.

Question 9

What does The Chromatin remodeling complex do?

Answer 9

• It locally repositions the DNA wrapped around nucleosomes.
• It uses the energy derived from ATP hydrolysis to loosen the nucleosomal DNA and push it along the histone octomer, thereby exposing the DNA to other DNA binding proteins.
• in some cases the repositioning of nucleosomes decondenses the chromatin in a particular chromosomal region and some cases it condenses the chromatin.

Question 10

What are some ways to alter chromatin Structure?

Answer 10

-Chromatin remodeling Complex
-reversible chemical modification of the histones
(Histone Tail modifications)

Question 11

What is Heterochromatin?

Answer 11

• It’s the most highly condensed form of interphase chromatin
• It makes up about 10% of an interphase chromosome
• In mammalian chromosomes its concentrated around the centromere region and in the telomeres at the ends of the chromosomes.

Question 12

What is Euchromatin?

Answer 12

-Its the rest of the interphase chromatin
-Greek meaning “true or normal”
-

Question 13

Because Heterochromatin is so compact…..

Answer 13

• Most the DNA that’s permanently folded into it in the cell does not contain genes
• Its b/c Heterochromatin is so compact, genes that accidentally become packaged into theses usually fail to be expressed. Can cause Disease

Question 14

The genetic material of a eukaryotic cell is contain in a set of _________, each formed from _____________.

Answer 14

• Chromosomes

- Single, enormously long DNA molecule that contains many genes.

Question 15

In the nucleosome core particle, _________.

Answer 15

DNA is tightly wrapped around a disc-shaped histone octamer.