Question

What are introns?

Answer 1

An intron is present in the intragenic region for genetic material that can be removed after transcription, when m-RNA is already formed. The process of removing these introns is called RNA splicing and helps in maturation of m-RNA.

Complete answer:
Central dogma of life is transcription of DNA to RNA then translation of RNA to protein. Intron is that part of encoded DNA which does not code for protein. So, it is important to remove this intron part. The process of removal of introns from RNA is known as RNA splicing.
After this process all the remaining parts called as exons are joined together to undergo translation and form proteins. Introns are found in genes of most of the organisms. But the frequency of occurrence may vary among the different species. But as RNA splicing mechanism is absent in the prokaryotic organisms thus, they do not have introns in the genes.
Introns can be of four different types that is:
Introns in nuclear protein-coding genes: These introns can be removed with the help of spliceosomes, also known as spliceosomal introns.
Introns in nuclear and archaeal transfer: Introns that can be removed by protein are known as tRNA introns.
Self-splicing group-I introns: This type of introns can be removed by RNA catalysis.
Self-splicing group-II introns: This type of introns can be removed by RNA catalysis.
There is another fifth type of introns, Group III introns but they are not well studied.

Note: Alternative splicing is the process which is responsible for the production of multiple proteins from single gene or single transcript of RNA. Alternative splicing can be controlled by a complex network of signalling molecules which respond to many intracellular and extracellular signals.