Question

What is the role of biotin in labelling DNA?

Answer 1

Hint: Biotin is a vitamin that is involved in a wide range of metabolic processes in humans as well as in other organisms. The name biotin is defined from the Greek word “bios” which stands for to live.

Complete answer:
Biotin is often used in the detection of proteins and nucleic acids, a process known as biotinylation. Biotinylation is rapid, specific and generally does not disturb the structure of the molecule that it binds to. Biotin is used for labelling DNA because biotin has an affinity for the nucleotide Uracil. During a PCR reaction if we use biotinylated uracil it will bond with all the adenine residues present in the given stretch of the DNA. This in turn will help us determine the sequence of the DNA. Biotin itself cannot be located, it is known to bind with streptavidin. Binding of biotin to streptavidin is very rapid and specific. Now this conjugated biotin when seen against an X-ray plate gives a black spot from where we can determine the position of adenine residues in the DNA and in turn the sequence of the DNA. The biotin streptavidin complex is resistant to extremes of heat as well as pH conditions thus making the detection quite accurate.

Note:
Apart from DNA, biotin is widely used for the detection of proteins as well. The biotin bounded proteins can be separated using a column where the beads are tagged with streptavidin. Biotin can be conjugated to many different chemical groups such as amines, sulfhydryls, carboxylates and carbohydrates. Thus it can also detect post-translationally modified proteins.