Restriction Enzymes | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Restriction Enzymes

• In 1970, it was found that bacteria produce enzymes capable of breaking down foreign DNA entering the bacterial cell. These enzymes are crucial for host restriction, a defense mechanism where bacteria safeguard themselves from viruses by fragmenting viral DNA.

• Restriction enzymes are named using a standardized method: the first letter of the genus name, followed by the first two letters of the species name, and additional letters representing strain or discovery order. For instance, Bam HI originates from Bacillus amyloliquefaciens, with 'H' denoting a specific strain and 'I' indicating its order of discovery.

• These enzymes bind to specific DNA sequences called recognition sequences and cleave the DNA at precise sites within these sequences. Recognition sequences are often palindromic, meaning they read the same forwards and backwards.

• Some enzymes like Smal cut both strands at the same position, resulting in blunt ends. In contrast, enzymes like EcoRI cut each strand at different locations, creating sticky ends with unpaired nucleotides.

DNA Fragmentation and Electrophoresis

Introduction to DNA Cleavage:

• When a restriction enzyme is introduced to DNA, it cleaves the DNA at specific sites known as cleavage sites.
• This action results in the DNA being fragmented into pieces of varying lengths and weights.

Fragment Analysis through Gel Electrophoresis:

• After the DNA is fragmented, the mixture of these fragments is placed at one end of a gel for electrophoresis.
• During electrophoresis, the fragments move through the gel at rates inversely proportional to the logarithm of their weights.
• At any given point during electrophoresis, the gel displays different bands, each representing a distinct size of DNA fragment from the original mixture.

Interpreting Band Positions:

• Each band on the gel indicates the size of a particular DNA fragment.
• The position of each band is crucial in determining the size of the corresponding DNA fragment.

By utilizing restriction enzymes and electrophoresis, scientists can effectively analyze and characterize DNA fragments based on their sizes, enabling a deeper understanding of genetic information and molecular structure.