Q.How is a mature, functional insulin hormone different from its prohormone form?

Insulin is initially synthesized as an inactive precursor, called pro-insulin. The transformation into a mature, functional hormone involves significant structural changes.

The key differences are:

• Pro-insulin: This form contains an extra stretch of polypeptide, known as the C-peptide, which connects the A and B chains. It is a longer, inactive molecule. …

Insulin is a vital hormone, crucial for regulating blood glucose levels in the body. Its deficiency leads to diabetes. Before it can perform its critical function, insulin is initially synthesised as a precursor molecule, known as a prohormone, which then undergoes processing to become the mature, functional hormone. This understanding was particularly important in the development of recombinant protein therapeutics, specifically for producing human insulin using biotechnology.

The prohormone form of insulin, called proinsulin, is a single, long polypeptide chain. In humans and other mammals, this proinsulin molecule consists of three distinct polypeptide segments:

• Chain A
• Chain B
• An extra stretch called the C-peptide (connecting peptide)

These three chains are arranged in a specific sequence within the single proinsulin molecule. The C-peptide essentially links the A and B chains together, holding the entire molecule in a particular conformation.

For proinsulin to become a mature, functional insulin hormone, it must undergo a crucial maturation process. During this process, specific enzymes within the pancreatic beta cells cleave the proinsulin molecule. The key event here is the removal of the C-peptide. Once the C-peptide is excised, the remaining A and B chains are free to associate correctly.

The mature, functional insulin hormone is therefore composed of two short polypeptide chains:

• Chain A
• Chain B

These two chains are held together by disulfide bridges (sulfur-sulfur bonds). These disulfide bonds are critical for maintaining the specific three-dimensional structure of the mature insulin molecule, which is absolutely essential for its biological activity – its ability to bind to receptors and facilitate glucose uptake by cells.

In summary, the fundamental difference lies in their structure: …

Method — spot the ONE structural difference and its cause

Proinsulin = A-chain + C-peptide + B-chain (one long chain, inactive).

Mature insulin = A-chain + B-chain only, joined by disulphide bonds (C-peptide enzymatically removed). …