hierarchy of chromatin

Question 1

Different types of chromatin

Answer 1

Chromatin is DNA and proteins
Theres 2 types and the Euchromatin is unraveled and in the center of the nucleus and heterochromatin is tightly wound and is on the margin or the nucleus

Question 2

1st order of chromatin structure

Answer 2

nucleosome packages 200 bp and looks like beads on a string the bead is composed of octomer of proteins called a histone

Question 3

histones

Answer 3

Are really basic contain lots of K+ and R+
5 Families: H-1, (H2a, H2b)x2, H3, and H-4

Histone functions to scaffold the chromosomes, and inhibit transcription by binding DNA done through histone modification

Question 4

Histone modifications

Answer 4

Inhibition of Transcription:
Done through phosphorylation (of all Histone proteins) and methylation (of H-3)-> heterochromatin formation caused by binding to HP1 (non histone protein)

Activation of Transcription:
Done through acetylation via HATs (histone acetyltransferaces–> neutralize K and R and repel histone from DNA and forms euchromatin

Usually occur at specific amino acids located at the n-term of the tails of histone proteins that protrude from the nucleosome (carried out by histone modifying enzymes)

Epigenetic Modification (gene function change without DNA change)

Question 5

DNA methylation

Answer 5

adding a methyl (CH3) group to the C in CpG dinucleotides done by DNA methyltransferases DNMTs and this blocks the transcription factors

Question 6

How to stop DNA transcription

Answer 6

1. DNMT methylate C in CpG
2. Methyl group is bound by methyl binding proteins (MBPs)
3. MBPs recruit histone deacetylases (HDACs) which remove acytlations to tightly pack DNA
4. MBPs also recruit Histone methyl transferases (HMTs) which gets HP-1’s chromodomain to silence gene expression

Question 7

Transcribing chromatin properties

Answer 7

Transcribing chromatin does have nucleosomes does have histones so that the DNA doesnt get crazy:

but no H-1
1-2 nucleosomes are absent for promoter region
nuclease assessable
histones are acetylated

Question 8

HAT

Answer 8

specific HATs bind to specific grwoth factor signals that are bound to DNA

Question 9

2nd order of chromatin

Answer 9

30 nm Solenoid agregattes in high salt one cross section is 6 nucleosomes (6x 200= 1200 bp)

H-1 linker is required

Question 10

3rd order of chromatin

Answer 10

The LOOP
fifty solenoids (50 x 1200= 60 000 bp)

now we start seeing whole gene(s)

base of each loop attaches to nuclear matrix to enable replication and transcription, it also brings genses closer together

Question 11

4th order of chromatin

Answer 11

the miniband: 18 loops (18 x 60 k= 1 million bp)

Question 12

5th order

Answer 12

Chromosome: 75 minibands =75 mil bp

hyperphosphorylation= chromosome
cetromere= center of the same to anchor
teleomere= ends gggtta