DNA Full Form in English
Full form of DNA is deoxyribonucleic acid.

What is DNA?


  DNA is the genetic material of most organisms except in some viruses, RNA is the genetic material.
Discovery of DNA:-

DNA was discovered by F. Meischer .
The term DNA was given by Zacharias.

1st time Wilkins and Franklin studies DNA molecules with the help of X-Ray crystallography. With the help of the study of X-Ray crystallography, Watson and Crick in 1953 proposed a double helix model of DNA for this model Watson and Crick and Wilkins awarded by Nobel Prize in 1962.

In a cell where DNA present:-

In eukaryotes DNA is present in nucleus and cytoplasm. In prokaryotes, DNA is present only in the cytoplasm. In prokaryotes circular DNA is present.
Some properties of DNA
1.DNA is a genetic material of most of the organisms because it is self-replicating Proofreading and self-repairing. 2.DNA  having a property called complementary and antiparallel.

DNA DOUBLE HELIX MODEL:-

According to this model, "DNA is composed of two polynucleotide chains" both chains are complementary And parallel to each other.
              In both strands of DNA direction of phosphodiester bond is opposite that is if the direction of phosphodiester Bond in one strand is 3'-5' then it is 5'-3' in another stand. Both strands of DNA are held together by hydrogen bonds. These hydrogen bonds are present between nitrogen bases of both strands.

Four types of nitrogenous base found in DNA that is
1.adenine.
2.thymine.
3.guanine.
4.cytosine.
            Adenine binds to thymine by two hydrogen bonds and cytosine binds to guanine by three hydrogen bonds.
In a DNA molecule, one purine always pairs with a pyrimidine. This generates approximately uniform distance between the two strands of DNA.
Configuration of DNA Molecule:-

     Two strands of DNA are helically coiled like a revolving ladder.  The backbone of this ladder is composed of phosphate and sugar while steps are composed of pairs of nitrogenous bases. The distance between two successive steps is 3.4 angstrom. One complete turn of the DNA molecule has 10 steps. so the length of one complete turn is 34 angstrom.

  The length of one complete turn of DNA is 34 angstrom this is known as helix length. The diameter of the DNA molecule to stand is 20 angstrom.
 Types of DNA:- 

on the basis of the direction of twisting, there were two types of DNA 
1. Right-handed DNA
2.left handed DNA
1. Right-handed DNA:-

   In right-handed DNA there was clockwise twisting of two strands of DNA.
It is of four types that are
1.' A' DNA
2.'B'DNA
3.'C'DNA
4.'D' DNA


The DNA for which Watson and Crick proposed model was B DNA

2.Left-handed DNA 
Anti clock wise twisting ex- 'Z'DNA


.
DNA packaging:-
DNA packaging in prokaryotes:-
DNA is found in cytoplasm in a supercoiled state. The coils are maintained by non-histon basic protein-like polyamines. This compact structure of DNA is called a genophore or nucleoid.
DNA packaging in eukaryotes:-
In eukaryotes DNA packaging is carried out with the help of lysine and arginine which basic proteins called histone. Basic unit of DNA compaction is known as a nucleosome. There are five types of histone protein found in eukaryotes H1,  H2A, H2B, H3, and H4.
Histone octamer is made up of 2 copies of each of H2A, H2B, H3, and H4 histone protein this is the core of nucleosome.
The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called nucleosome.
A typical nucleosome 200 base pair of DNA helix. Two adjacent nucleosome  is linked by linker DNA. linker DNA is attached to H1 histone protein.  Nucleosome in chromatin Gives beats on string appearance under electron microscope.
A nucleosome consists of repeating unit of a structure is nucleus called chromatin . Chromatin is a thread-like structure that is present in the nucleus . At a Higher level of packaging, some proteins are required known as non-histone chromosomal protein.
Length of DNA double helix in a typical mammalian cell is 2.2 m approximately.
    Length of E. Coli DNA is 1.36 mm

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