MINISTRY OF DEFENCE

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  MINISTRY OF DEFENCE. Establishment Of National University In Islamabad Total position. 29 Domicile , All over Pakistan    Qualification  intermediate to bachelor positions . Project Engineer(Civil) account Officer  supervisor assistant office boy     How to apply.   Apply online through the link https://www.fgei-cg.gov.pk/nup-rec.php   Last date to apply  02 April 2023. No TA/DA Fo Interview 
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Chemical,Molecular and ultrastructure of Chromosome

Molecular,Chemical and ultar Structure Of chromosomes:

Dupraw and Hans Ris proposed the theory about the molecular structure of chromosome, called Unistranded theory.
According to this theory the chromosome consist of an elongated coiled fibre,called nucleo-protein fibre.in this fibre a double stranded DNA is present.The DNA is covered by histone and non histone proteins and RNA.the histone and non histone protein are equal in number.
When in prophase stage,chromosome is treated with acetocaramine ,two distinct regions of chromosome are visible according to the amount of proteins,DNA And RNA.

1.Euchromatin regions 2 Heterochromatin regions


1.Euchromatin regions

Closely packed and stains dark and transcriptionally active.

2.Heterochromatin Regions

In 1928 Heitz
The chromatin that is more densely packed and stained dark and inactive.
Two types of Heterochromatin

A Facultive Heterochromatin

Some time condense some time uncondense.

B.Constitutive Heterochromatin

In such a Heterochromatin the DNA is permanently inactive & remains in the condensed state throughout the cell cycle.


Chemical Structure of chromosomes.

Chemically the chromosomes consist of:
1. Nucleic Acid l:DNA & RNA
2. Proteins:of two types Histones (basic proteins or non acidic proteins)
And Non-Histone proteins(Acidic proteins)
3.metallic ions

1 Nucleic Acid

* in chromosome the nucleic acids are present in the form of DNA (Decoy ribonucleic acid) and to some extent as RNA(ribonucleic acid).
*DNA is found in genes.in all diploid cells its amount is almost constant. During meiosis it divides and its half amount is transferred into sperms and ova.the DNA of the chromosomes is the genetic material.

*RNA is associated with DNA in little amount.it takes part in protein synthesis.
*the DNA of human chromosome about 140 nucleotides are present.in electron microscope the DNA looks like a string of beads.these beads or knob like structure are called Nucleosomes.( 8 proteins are joined together by two turns of DNA)
*each nucleosome is about 110A° in diameter and 60A°.

2.Proteins of chromosome:

In chromosome two types are present:
A. Histone proteins (basic proteins)
B.Non histone proteins (Acidic proteins)
A Histone proteins( Basic proteins )
These proteins are basic proteins and regulate the structure and function of chromosome DNA.
   Histone proteins are of five different types:
H1,H2a,H2b,H3,H4
B.Non histone proteins ( Acidic proteins )
The proteins have regulatory and enzymatic function.they also control the physical properties of genes e.g Phospho proteins,RNA polymerase and DNA polymerase.


Metallic ions 

Many metallic ions are present in chromosome such as Mg,Ca etc.they make the organization of chromosomes.


*Ultrastructure of chromosome:

     in chromosome two type of proteins are present Histone and Non histine, we know that histone proteins are of 5 types. The Histone proteins are associated with DNA to form basic subunits of chromatin called nucleosomes.
Histone proteins are rich in amino acids and these  are positively charged due to the presence of two amino acids arginine and lysine.
      Histone help in the organization of nucleosome,each nucleosome contains 146 nuckeotide pairs if DNA.
      The DNA double helix is coiled around a central core of histones,this central core consists of eight molecules of histone proteins,called octamer.in this octamer two molecules of each histone H2A,H2B,H3 and H4 are present,(H1 work as a pin),part of DNA that connects nucleosome is called linker DNA.A complete repeat unit consists of 200 base pairs (bp) of DNA and octamer.

 Solenoid Model

When many nucleosomes are joined together to form a structure called solenoid.

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