Explain how the reduction of disulfide bonds in insulin affects its three‑dimensional structure and its ability to bind to the insulin receptor, describing the structural changes and functional outcome.
Answer
Reduction of insulin’s disulfide bonds cleaves the two inter‑chain and one intra‑chain linkages, separating the A and B chains and disrupting the native folding. The loss of the cystine‑bridged scaffold leads to loss of the receptor‑binding conformation, resulting in a dramatic drop in receptor affinity and hence a loss of biological activity.
Step-by-step solution
- Identify the disulfide bonds in insulin: two inter‑chain bonds (A‑B) and one intra‑chain bond on the A chain.
- Describe the reduction reaction: , breaking the bridges.
- Explain the consequence: the A and B chains are no longer covalently linked, and the cystine network that stabilises the folded structure is destroyed.
- State the structural impact: the protein unfolds or adopts an altered conformation with the active‑site geometry perturbed.
- Conclude the functional outcome: the receptor‑binding surface is lost, so insulin can no longer stimulate glucose uptake, effectively abolishing its biological activity.
Common mistake: Assuming only inter‑chain disulfides are affected and neglecting intra‑chain bond importance
Concept tested: Effect of disulfide bond reduction on protein structure
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