Hierarchy of Chromatin Structure

Question 1

Hierarchy of Structure

Answer 1

Nucleosome, 30 nm fiber, Chromatin Loop, Miniband, Chromosome

Question 2

Number of Nuclei Erythrocyte

Answer 2

0 via Extrusion

Question 3

Number of Nuclei Cardiocyte, Hepatocyte

Answer 3

1-2 via Nuclear Division

Question 4

Number of Nuclei Osteoclast

Answer 4

3-10 via Fusion of Precursors

Question 5

Number of Nuclei Skeletal Myocytes

Answer 5

100+ via Fusion of Myoblasts

Question 6

Chromatin Types and Function

Answer 6

Heterochromatin: Highly dense, transcriptionally inactive, 10%
Euchromatin: Less dense, can be active

Question 7

Nucleosome structure

Answer 7

200 bp of DNA, octamer of proteins from core families (H2A, H2B, H3 and H4) with DNA wraapped around this bead (140 BP). High in K+ and R+ residues. Linked with H1 (60 BP)

Question 8

Histone Acetylation

Answer 8

Neutralizes positive charge on K and R, repulsing histones from DNA sites

Question 9

Histone Methylation

Answer 9

H3 causes formation of heterochromatin

Question 10

Histone Phosphorylation

Answer 10

Condensation of chromatin for mitosis

Question 11

Location of histone modifications

Answer 11

Amino-Terminal Tails

Question 12

DNA Methylation

Answer 12

Methyl addition to cytosine on 5’ carbon of base in CpG dinucleotides, blocking TFs from binding, conducted by DNA methyltransferases (DNMTs)

Question 13

DNA Methylation/Chromatin Condensation Cascade

Answer 13

Methyl CpG binding proteins (MBPs) find methylated CpGs
MBPs recruit histone deacetylases (HDACs) and Histone Methyltransferases (HMTs)
HDACs increase K and R charge, causing histones to more tightly bind to DNA, reducing expression
HMTs methylate histones to completely silence expression

Question 14

Effect of histone modification on tumor suppressor genes

Answer 14

Epigenetic modifications been shown to suppress tumor suppressor genes, causing high cell growth
Treated with DNMT and HDAC inhibitors

Question 15

DNMT Inhibitors

Answer 15

5-azacytidine (Vidaza) and 5-aza 2’ deoxycytidine (Decitabine)

Question 16

HDAC inhibitors

Answer 16

SAHA (Vorinostate), Phenylbityrate, Valproic acid

Question 17

Histone Acetyl Transferase Cascades

Answer 17

HATs are recruited by TFs to acetylate histones for expression, also one or two histones may be dissolved for opening the promoter sequence

Question 18

30-Nanometer Fiber structure

Answer 18

6 Nucleosomes form 1200 bp fiber (per solenoid turn) , H1 facilitates construction, 30 nm refers to solenoid diameter

Question 19

Loop structure

Answer 19

On average 50 30 nm fibers coiled into loop for 60,000 bp, leading to supercoiling
Bases of loops are attached to nuclear matrix which have machinery for gene regulation/expression

Question 20

Loop function

Answer 20

Downstream and upstream interaction of gene allows for it to interface with nuclear matrix, regulating expression

Question 21

Minibands structure

Answer 21

18 loops to form roughly 10^6 bp

Tandems of loops that encircle chromosome axis

Question 22

Mitotic Chromosomes structure

Answer 22

On average 75 minibands come together so 75 mil BP

Includes centromere and two telomeres

Question 23

Centromere structure

Answer 23

Repetitive DNA in middle of chromosomes

Question 24

Telomere structure

Answer 24

Repetitive DNA (GGGTTA in humans) which cap ends of chromosome

Question 25

Telomere function

Answer 25

Shortens with each division until cell senescence is achieved in somatic cells
Germ line cells have telomerase to continue permitting division
When telomerase is activated in somatic cells it results in cell immortality