Human insulin molecule is composed of one a-chain having 21 amino acids and one P-chain having 30 amino acids. How many functional insulin genes occur in adult humans?

Human insulin is a 51-residue anabolic protein composed of two polypeptide chains: an A-chain with 21 amino acids and a B-chain with 30 amino acids [3]. These chains are linked by disulfide bonds. In humans, insulin is the biosynthetic product of a single-chain precursor called preproinsulin, which is encoded by a single functional gene known as the INS gene located on chromosome 11 [2]. While some species, such as rodents, possess two functional insulin genes due to gene duplication, the human genome contains only one functional insulin gene [1]. Although the human genome contains other members of the insulin superfamily, such as insulin-like growth factors (IGF1, IGF2) and relaxins, these are distinct genes with different functions. Therefore, adult humans have only one functional gene responsible for producing the insulin hormone [2].

Sources

1. [2] https://www.ncbi.nlm.nih.gov/books/NBK279029/
2. [3] https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/human-insulin
3. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC8051583/