Applications Of Biotechnology

Polymerase Chain Reaction (PCR) is a technique used to amplify specific segments of DNA. The process involves repeated cycles of heating and cooling:

• Denaturation: Heating the DNA to high temperatures (typically ~95°C) to separate the double helix into single strands.
• Annealing: Cooling the reaction to allow primers to bind to the complementary sequences on the single-stranded DNA.
• Extension: Raising the temperature slightly (typically ~72°C) to allow a DNA polymerase to synthesize new DNA strands, starting from the primers.

Because the cycle involves high temperatures during the denaturation step, the DNA polymerase used must be thermostable (heat-stable) so that it doesn't get denatured and inactivated after each heating cycle.

The first widely used and still very common thermostable DNA polymerase for PCR is Taq polymerase.

This enzyme was isolated from a thermophilic bacterium that thrives in hot springs.

Let's look at the options:

• Thermus aquaticus: This is a species of bacterium that can tolerate high temperatures. It was originally isolated from hot springs in Yellowstone National Park. Taq polymerase is named after this organism (Thermus aquaticus). This is the correct source.
• Agrobacterium tumifaciens: This bacterium causes crown gall disease in plants and is famously used in plant genetic engineering due to its Ti plasmid, but it is not the source of Taq polymerase.
• Bacillus thuringiensis: This bacterium produces Bt toxins, which are used as insecticides in agriculture and genetic engineering, but it is not the source of Taq polymerase.
• Salmonella typhimurium: This bacterium is known for causing food poisoning (salmonellosis) and is used in the Ames test for mutagenicity. It is not the source of Taq polymerase.

Therefore, Taq polymerase used in PCR is obtained from Thermus aquaticus.

Yes, gel electrophoresis is used for the separation of DNA fragments according to their size.

How it Works:

DNA samples are loaded into wells in an agarose gel and subjected to an electric field.

Since DNA is negatively charged due to its phosphate backbone, it moves towards the positive electrode (anode).

Smaller DNA fragments migrate faster and farther, while larger fragments move slower and remain near the wells.

DNA bands are visualized using staining agents like ethidium bromide (EtBr) or SYBR Green under UV light.

Applications:

DNA fingerprinting

PCR product analysis

Checking restriction enzyme digestion

DNA sequencing

Genetic disorder diagnosis

Thus, gel electrophoresis is a key technique for DNA fragment separation based on size.