Packaging of DNA

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PowerPoint Presentation : Packaging Of DNA Helix

Why Packaging is Needed? : Why Packaging is Needed? DNA is roughly 3 meter long and it has to be packed in nucleus which is few micrometres in diameter , hence higher order of packaging is required There are various order of packaging First order of packaging – Nucleosome Second order of packaging – Solenoid fibre Scaffold loop Chromatids Chromosome

Packaging of DNA : Packaging of DNA

Nucleosome – First order of compaction : Nucleosome – First order of compaction Nucleosomes are fundamental repeating subunits of all eukaryotic chromosomes except those of sperms. The nucleosome consists of about 200 bp wrapped around a histone octamer that contains two copies of histone proteins H2A, H2B, H3 and H4. The DNA that is between each histone octamer is called the linker DNA Proposed by Roger Kornberg Term nucleosome was coined by P.Oudet

Nucleosome : Nucleosome H2A & H2B together forms dimer Two molecules of H3 & H4 together form tetramer Two dimer & one tetramer together form one octamer DNA is wrapped around an octamer having 200 bp. Octamer + 200 bp DNA = Nucleosome

Nucleosome : Nucleosome Nucleosome is spheroid having diameter of 110 A 0 or 11 nm & width of 50-55 A 0 No. of turn of DNA / Nucleosome = 1.75 Out of 200 bp of DNA,146 bp are tightly bounded to octamer – Core DNA The DNA that is between each histone octamer is called the linker DNA and can vary in length from 8 to 114 base pairs No. of bp in linker DNA is species specific

Nucleosome : Nucleosome Core Particle 146 bp of DNA wrapped around outside of an octamer of Histone Chromatosome Core particle interacts with one molecule of H1 histone to form a particle containing 166 bp of DNA Nucleosome Chromatosome links with linker DNA to form nucleosome containing 200 bp of DNA

PowerPoint Presentation : Chromosome – Proteins Histone Non - histone Chromosomal Proteins Histone proteins are basic and Non-histone Proteins are acidic in nature Histone Suppress gene action whereas Non-histone Promotes gene action

Histone proteins : Histone proteins Five types of Histone proteins – H 1 , H 2 A, H 2 B, H 3 , H 4 H 1 , H 2 A & H 2 B, are rich in lysine whereas H 3 & H 4 are arginine rich H 1 is highly unconserved and mutable H 3 & H 4 are highly conserved molecules According to molecular weight the relation is H 1 > H 3 >H 2 A >H 2 B >H 4 Histone proteins lack Tryptophan Molecular weight of Histone protein is approximately 25,000 dalton

Non-histone protein : Non-histone protein Higher molecular weight - Approximately 1.0 to 1.5 lakh dalton Acidic in nature Mostly act as enzyme Promotes gene action

Solenoid – Second level of packaging : Solenoid – Second level of packaging Proposed by Finch & Klug 6 nucleosome together forms Solenoid Diameter is 30 nm H1 histone stabilizes the Structure

PowerPoint Presentation : Solenoid

Super Solenoid : Super Solenoid The final level of packaging is characterized by the 700 nm structure seen in the metaphase Chromosome known as super solenoid structure. The condensed piece of chromatin has a characteristic scaffolding structure that can be detected in metaphase chromosomes. This appears to be the result of extensive looping of the DNA in the chromosome.

Class Exercise : Class Exercise DNAase enzyme degrades DNA. A nuclesome is treated with DNAase. Number of base pairs remaining intact are 200 146 54 246 Hint: Enzyme cannot degrade tightly bounded DNA Send your answer to and get free video lessons

References : References

PowerPoint Presentation : Check out for other Lessons……… Structure of DNA DNA is a Genetic Material Some other forms of DNA RNA Types of RNA DNA Replication Transcription Translation Operon Concept For Complete Video lessons of Genetics write to us at

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