DNA Packaging

1. Chromatin Modulation
and its Role in Gene
Regulation

2. Presented By:
 MUHAMMAD Zain Ahsan
 Amber Ayyaz
 Talha Mazhar
 Hamza Khan

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)

5. Walther Fleming stained chromatin

6. DNA to Chromosome

7. Chromatin structure in cell cycle

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.

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

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

17. Nucleosome disruption
Inactive ground state
ATP
Derepressed state
More accessible
Closed

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

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.