Lecture 8 DNA Packaging

Question 1

How big is the human genome

Answer 1

3200 mb of DNA in a haploid cell.

Question 2

How is the human genome organized

Answer 2

It is split into 24 linear DNA molecules.

Question 3

What is Chromatin

Answer 3

It is a DNA Protein complex. The proteins are spaced along regular intervals along the DNA.

Question 4

How was the structure of Chromatin deduced

Answer 4

Using endonuclease digestion to digest the Chromatin.

Question 5

What is the name used to describe the structure of Chromatin

Answer 5

Beads on a string structure.

Question 6

What are the names of the proteins in Chromatin

Answer 6

Histone proteins

Question 7

Give the name of 5 Histones mentioned in lecture slides

Answer 7

H1
H2A
H2B
H3
H4

Question 8

Is H1 a histone or a family of histones

Answer 8

H1 is a family of histones, and includes H1 a - e, H1t and H5

Question 9

Which histones are in the H1 family

Answer 9

• H1a - e
• H1
• H1t
• H5

Question 10

In the beads on string structure, which structure is represented by the beads

Answer 10

Nucleosomes

Question 11

What is a nucleosome

Answer 11

(The beads on the string)
Each nucleosome is an octamer of 8 proteins.
It contains 2 each of histones H2A, H2B, H3, H4.

Question 12

What is the role of histone H1

Answer 12

• It is the linker histone

- It attaches outside the nucleosome.

Question 13

Describe the structure of a chromatosome

Answer 13

A chromatosome describes the combination of the nucleosome, plus DNA plus linker histone.

Question 14

Explain the difference between the nucleosome and the chromatosome

Answer 14

Nucleosome simply refers to the octameric protein of 8 histones. The chromatasome refers to the nucleosome plus DNA plus linker histone plus.

Question 15

Describe the role of Histone H1

Answer 15

Histone h1 is the linker histone

Question 16

What is the effect of the beads on a string level of packaging on the length of DNA

Answer 16

Beads on string reduces DNA length to 1/6th of its total length.

Question 17

Describe the order of packaging

Answer 17

• Beads on a string

- 30nm chromatin fiber

Question 18

What is the effect of the 30nm chromatin fibre on the overall length of the DNA

Answer 18

Reduces the overall length of the DNA to by a futher 1/7th.

Question 19

How long is the length of the DNA molecule in chromosome 8

Answer 19

4.9cm

Question 20

What is the effect of the 30nm chromatin fiber on DNA length in chromosome 8

Answer 20

4.9cm is reduced to 1.2 mm

Question 21

What is the highest level of DNA packaging currently known

Answer 21

The metaphase chromosome.

Question 22

Where is the metaphase chromosome found

Answer 22

Only in dividing cells

Question 23

What is Euchromatin

Answer 23

transcriptionally active chromatin, it appears light under microscope. It contains active genes

Question 24

What is heterochromatin

Answer 24

transcriptionally inactive chromatin, supercoiled, it appears dark, and on the edges of the nucleus. Contains inactive genes.

Question 25

What are the two types of heterochromatin

Answer 25

- Constitutive heterochromatin | - Facultative heterochromatin

Question 26

What is constitutive heterochromatin

Answer 26

it contains DNA that is always tightly packed in every single cell

Question 27

What is facultative heterochromatin

Answer 27

It contains DNA that is tightly packed only in some cells

Question 28

What is the role of the nucleolus

Answer 28

Nucleolus contains ribosomal RNA genes and is the site of ribosome biogenesis . ribosome production.

Question 29

Describe the state/levels of packaging of DNA in Euchromatin

Answer 29

- DNA in form of 30 nm chromaitn fibre | - attached to the nuclear matrix and nuclear lamina.

Question 30

Why is Euchromatin DNA attached to the nuclear lamina and nuclear matrix

Answer 30

So that it does not get tangled up.

Question 31

List the names of some nuclear matrix and nuclear lamina associated diseases

Answer 31

- Progeria - Downs' syndrome - Huntingtons disease

Question 32

Describe the role of the centromere in the metaphase chromosome

Answer 32

Centromere holds the daughter chromsomes together, and it contains special histones - CENP-A instead of H3.

Question 33

Describe the role of the telomeres in metaphase chromosome

Answer 33

Telomeres protect the ends - from exonuclease attack - from being mistaken for chromosome breaks and joined together.

Question 34

Telomeres protect chromosomes from

Answer 34

- From exonuclease attack | - from being mistaken for chromosome breaks and joined together.