3. Contents:
Introduction
DNA to Chromosome
Chromatin structure
Types of chromatin
Functions of chromatin
Chromatin re-modeling
Chromatin re- modeling methods
Chromatin role in gene regulation
Importance of gene regulation
4. Introduction
The DNA in eukaryotic cells is extensively folded and packed into the protein-
DNA complex called chromatin.
Histones proteins are an important part of this complex.
DNA protein complex is called nucleosome.
Walther Fleming discovered chromatin in 1878 while study cell division.
He stained the cells of salamander with alanine dye.
He observed that some portion of genetic material absorbed dye more than other
parts.
He named it chromatin ( Chroma is Greek word mean color)
8. Types of chromatin
Two types of chromatin
In 1928 Emil hitez used term euchromatin and heterochromatin
Euchromatin
It is a loosely packed form of chromatin and rich in gene concentration.
It is comprises the most active portion of genome
It is truly transcribing portion of DNA.
This portion is called “string on the beads”
This structure appears mostly in interphase or growth phase of the cell cycle.
9. Heterochromatin
It is tightly packed form of the chromatin.
This region of chromosome is more condensed and stained deeply with
different dyes.
Two basic types
1. Facultative Heterochromatin
It comprises most of the silenced genes
2. Constitutive Heterochromatin
It makes the structural and functional forms of chromosome like
Centromere
Telomere
Bothe are involved in gene expression.
Both are transcriptionally inactive.
10.
11. Role of chromatin
DNA packaging into more compact form
Reinforce the DNA macromolecules to allow mitosis
Prevent DNA from damaging
Regulation of gene expression
Regulation of DNA replication
12. Chromatin re modeling
What is meant by Re-Modeling ?
Why we need it ?
Why chromatin compaction occur ?
why gene containing portion of DNA wrapped on Histones?
What are histones ?
Two types
1.Core histones proteins
2.Linker histone proteins
Dimerization
Homodimer
Heterodimer
13.
14.
15.
16. Chromatin Re- Modeling Methods
Direct nucleosome mobilization method
It is a ATP dependent method
SWI/SNF complex is involved
SNF specific for sucrose fermenting gene
This complex require some transcriptional factors for activity.
SWI/SNF can modulate chromatin by 3 mechanisms
It recognize the acetylated histone protein
1. Nucleosome disruption
2. Nucleosome sliding
3. Nucleosome transfer
18. Three possible activities of Swi/Snf
Nucleosome
remodeling
Nucleosome
sliding
Octamer
transfer
TF
TF
TF
TF
TF
TF
19. Histone modifications
Histone can be modified by
Methylation
Acetylation
Phosphorylation
Ubiquitnation
De methylation
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22.
23.
24. Chromatin role in gene regulation
Positive control
Transcription on
Activation occurs due to
1. Readers
2. Writers
Negative control
Transcription off
Repression occurs due to
1. erasers
25. Importance of gene regulation
Control the amount of gene product
Allow cells to adjust with changing conditions
Expression of gene at proper time.
Prevent the wastage of cell energy.
