11.2 Chromosome structure and compaction

Question 1

How is DNA in a cell if it is stretched out?

Answer 1

about 6 feet/ 2 meters long

Question 2

What are the three levels of chromosome compaction?

Answer 2

1. Nucleosome
2. Supercoiling
3. Radial loop- scaffold

Question 3

give the status and function of nucleosomes

Answer 3

status: Confirmed by crystal structure
function: Condense naked DNA 7-fold to a 100A fiber

Question 4

Give the function of supercoiling

Answer 4

causes an additional 6-fold compaction, achieving a 40- to 50-fold condensation relative to naked DNA.

Question 5

What is the function of radial loop-scaffolding ?

Answer 5

Through progressive compaction of 300A fiber, condenses DNA to rodlike miotic chromosomes that are 10 000 times more compact than naked DNA.

Question 6

What structure is the fundamental unit of chromosomal packaging?

Answer 6

Nucleosome

Question 7

What is the structure of nucleosomes?

Answer 7

they resemble beads on a string ( histones forming the core and DNA wound around them)

Question 8

In what two ways do spacing and structure of nucleosomes affect genetic function?

Answer 8

1. Accessibility for proteins that initiate transcription, replication and further compaction
2. Arrangement along chromatin is highly defined and varies in different cell types and under different conditions.

Question 9

The nucleosome core is an ___________ of two each of the histones; H2B, H2B, H3, and H4

Answer 9

octamer

Question 10

explain the wrapping process of DNA around histones:

Answer 10

160bp of DNA wraps twice around a nucleosome core. 40 bp of linker DNA connects adjacent nucleosomes. Histone H1 associated with linker DNA as it enters and leaves the nucleosome core.