Human insulin molecule is composed ofone α-chain having 21 amino acids andone β-chain having 30 amino acids. How many functional insulin genes occur in adult humans?
One
Understanding Functional Insulin Genes in Humans
The question asks about the number of functional genes that encode for insulin in adult humans. Insulin is a crucial hormone involved in regulating blood sugar levels.
As the question mentions, the mature human insulin molecule is composed of two polypeptide chains:
- An α-chain consisting of 21 amino acids.
- A β-chain consisting of 30 amino acids.
These two chains are linked together by disulfide bonds in the mature protein.
How is Insulin Produced from a Gene?
Despite having two chains, the insulin molecule in humans is encoded by a single functional gene. This gene is located on the short arm of chromosome 11 (specifically at locus 11p15.5).
The process from gene to mature insulin involves several steps:
- The insulin gene is transcribed into messenger RNA (mRNA).
- The mRNA is translated into a precursor protein called preproinsulin. This is a single polypeptide chain that includes a signal peptide, the B chain, the C-peptide, and the A chain (in that order).
- The signal peptide is cleaved off as the protein enters the endoplasmic reticulum, resulting in proinsulin. Proinsulin is a single folded chain with disulfide bonds forming between regions that will become the A and B chains.
- Proinsulin is transported to the Golgi apparatus and then to secretory vesicles.
- Within the secretory vesicles, the C-peptide is cleaved out by enzymes (proteases). This leaves the mature insulin molecule, which consists of the A and B chains linked by disulfide bonds. The C-peptide is also released into the bloodstream.
Therefore, even though the final hormone has two chains, they originate from a single polypeptide precursor molecule encoded by one functional gene.
Number of Functional Insulin Genes
In adult humans, there is typically only one functional gene encoding insulin (the INS gene on chromosome 11). While pseudogenes or gene variations might exist in the genome, only this one gene is actively transcribed and translated to produce functional insulin.
Based on the understanding of human genetics and insulin synthesis, the number of functional insulin genes in adult humans is one.
Revision Table: Key Facts About Human Insulin Gene
| Feature | Description |
|---|---|
| Number of Functional Genes | One (1) |
| Gene Name | INS |
| Chromosome Location | Chromosome 11 (11p15.5) |
| Encoded Product (Initial) | Preproinsulin (single polypeptide) |
| Mature Insulin Structure | α-chain (21 amino acids) + β-chain (30 amino acids), linked by disulfide bonds |
Additional Information: Insulin Processing
The cleavage of proinsulin into mature insulin and C-peptide is an essential step for insulin activation. The C-peptide is often measured clinically as an indicator of endogenous insulin production because it is released in equimolar amounts with insulin. This detailed processing highlights how a single gene can give rise to a mature protein with complex structure.
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