Chromosome structure

Question 1

The basic structure of chromosome is the ____, which is ____ in diameter.

Answer 1

elementary fibre; 10 nm

Question 2

The chromatin or the elementary fiber is composed of repeating units called _____, each consisting of eight histone molecules, around which 146bp of the DNA molecule is coiled 1.75 times

Answer 2

nucleosomes (10 nm)

Question 3

Composition of a nucleosome

Answer 3

8 histone molecules
146 bp of DNA coiled 1.75 times

Question 4

The elementary fibre of linked nucleosomes (which appears under the electron microscope as a string of 10nm ‘beads’) is, in turn, coiled into a ____ of ____ diameter.

Answer 4

chromatin fibre; 30nm

Question 5

The metaphase chromosome has a central scaffold formed of ____ protein to which the chromatin fibre is attached at ____ containing AT-rich repeated sequences.

Answer 5

acidic; scaffold attachment regions (SARs)

Question 6

Refers to the loop of chromatin fibers radiating out from the scaffold to form the body of the chromatid.

Answer 6

Laemli loops

Question 7

What is the diameter of chromatid?

Answer 7

0.6 µm

Question 8

The loops of chromatin are attached to the central scaffold by proteins such as _____ multimer.

Answer 8

scaffold attachment factor-A (SAF-A)

Question 9

This enzyme is a major component of the chromosomal scaffold, plays an important role in regulating the chromatin compaction necessary for mitosis. This enzymes achieves this by making a double-stranded cut in the DNA and passing an unbroken double strand through the gap before repairing it.

Answer 9

Topoisomerase II

Question 10

Heterochromatic areas are commonly located close to the what structures?

Answer 10

Telomeres; centromeres

Question 10

What are the histone/DNA modifications that promote transcriptional deactivation of heterochromatin?

Answer 10

Methylation of lysines 9 and 27 of histone H3
Methylation of lysine 20 of histone H4

Question 11

T/F. In contrast to areas of euchromatin, areas of heterochromatin contain few active genes and replicate late during S phase.

Answer 11

True.

Question 11

What are the modifications that promote transcriptional activation of the euchromatin region?

Answer 11

Local absence of 5-methylcytosine methylation of DNA
Acetylation of various histone tail amino acids
Methylation of lysines 4, 36 and 79 of histone H3.

Question 12

Heterochromatic areas often contain ____?

Answer 12

macro satellite DNA