DNA AND DNA FINGERPRINTING

DNA and DNA fingerprinting.

In this post, you are going to talk about dna and dna fingerprinting.

Main contain

1.1 what is DNA

1.2 DNA fingerprinting 

1.1 what is DNA 

* DNA as an acidic substance present in nucleus was first identified by Friedrich Meischer in 1869.

* DNA term was given by - Zacharis

* DNA is long polymer of deoxyribonucleotides.

* DNA is negatives charge.

* Wilkins and Franklin studied DNA molecule with the help of X-Ray crystallography.

* With the help of this study, Watson and Crick (1953) proposed a double helix molel for DNA. For this model Watson, Crick and Wilkins were awarded by Noble Prize in 1962.

* One main hallmark (main point) of double helix model is complementary base pairing between purine and pyrimidine.

* According to this model, DNA is composed of two polynucleotide chains.

* Both polynucleotide chains are complementary and antiparallel to each other.

* In both strand of DNA direction of phosphodiester bond is opposite. i.e. If direction of phosphodiester bond

in one strand is 3'-5' then it is 5'-3' in another strand.

* Both strand of DNA are held together by hydrogen bonds. These hydrogen bonds are present between nitrogen bases of both strand.

* 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.

1.2 DNA fingerprinting 

It is technique to identify a person on the basis of his/her DNA specificity.

This technique was invented by sir Alec. Jeffery (1984).

In India DNA Finger printing has been started by Dr. V.K. Kashyap & Dr. Lal Ji Singh.

DNA of human is almost the same for all individuals but very small amount that differs from person to person that forensic scientists analyze to identify people.

These differences are called Polymorphism (many forms) and are the key of DNA typing. Polymorphisms are most useful to forensic scientist. It is consist of variation in the length of DNA at specific loci is called Restricted fragment. It is most important segment for DNA test made up of short repetitive nucleotide sequences, these are called VNTRs (variable number of tandem repeat).

VNTR's also called minisatellites were discovered by Alec Jeffery. Restricted fragment consist of hypervariable repeat region of DNA having a basic repeat sequence of 11-60 bp and flanked on both sites by restriction site. The number and position of minisatellites or VNTR in restriction fragmnt is different for each DNA and length of restricted fragment is depend on number of VNTR.

Therefore, when the genome of two people are cut using the same restriction enzyme the length of fragments obtained is different for both the people.

These variations in length of restricted fragment is called RFLP or Restriction fragment length polymorphism. Restriction Fragment Length Polymorphism distributed throughout human genomes are useful for DNA Finger printing. DNA Fingerprint can be prepared from extremely minute amount of blood, semen, hair bulb or any other cell of the body.

DNA content of 1 - Microgram is sufficient.

Technique of DNA Finger printing involves the following major stpes.

Extraction – DNA extracted from the cell by cell lysis. If the content of DNA is limited then DNA can be amplified by Polymerase chain reaction (PCR). This process is amplification.

Restriction Enzyme Digestion : Restriction enzyme cuts DNA at specific 4 or 6 base pair sequences called restriction site.

Hae III (Haemophilus aegyptius) is most commonly used enzyme. It cuts the DNA, every where the bases are arranged in the sequence GGCC. These restricated fragment transferred to Agarose Polymer gel. 109 Gel Electrophoresis :

Gel electrophoresis is a method that separates macromolecules-either nucleic acid or proteins-on the basis of size, electric charge.

Gel electrophoresis refers to the technique in which molecules are forced across a span of gel, motivated by an electrical current. Activated electrodes at either end of the gel provides the driving force. A molecule's proper- ties determine, how rapidly an electric field can move the molecule through a gelatinous medium.

Nowadays the most commonly used matrix is agarose which is a natural polymer extracted from sea weeds. The DNA fragments separate (resolve) according to their size through sieving effect provided by the agarose gel. Many important biological molecules such as amino acids, peptides, proteins,