Question

(Molecular Biology) Explain what a gene is, and what isoforms are & how a gene can have 2 different isoforms, and further explain how exons can splice together to form the 2 different isoforms.

Answer 1

Gene is defined as the basic and fundamental unit of heredity. It is the smalles entity that is inherited from parents to offspring. Genes are generally made up of DNA. Some of these genes (structural genes) contain information which direct the production of proteins. At the same time, many genes do not code for a protein. Genes can vary in size frow a few hundred bases to 2 million bases or more. In case of humans, every person has two copies of a gene, each inherited from one parent. Alleles are different forms of DNA which are almost similar to the gene but differ in small sequences of DNA bases.

Gene isoforms are essentially mRNAs transcribed out of the same gene locus , with different Transcription Start Sites (TSSs) or protein coding DNA sequences (CDS) or untranslated regions (UTRs). These mRNAs thus code different proteins which could change the function of the gene i.e. either enhance the function or result in loss of function.

A gene can have 2 different isoforms since it can have multiple Transcription Start Sites, Termination sites and coding regions. This can result in production of mRNAs with different sizes and composition. Even a single deletion or addition of a base can lead to change in the reading frame of mRNA and thus produce very different protein which may or may not be functional.

Alternative splicing of exons can result in multiple combinatios of exons present within a single mRNA. Thus different combinations of exons can lead to production of different proteins with different functions. Thus in this manner exon splicing produces gene isoforms.