Detailed Explanation
The arrangement of multiple polypeptide subunits into a functional multi-chain complex. Not all peptides/proteins have quaternary structure — only those composed of more than one polypeptide chain.
Classic examples: hemoglobin (α₂β₂ — four subunits carrying oxygen), antibodies (two heavy + two light chains linked by disulfide bonds), insulin hexamers (six insulin molecules + two zinc ions — the storage form in β-cell granules). Quaternary interactions are stabilized by the same non-covalent forces as tertiary structure plus inter-chain disulfide bonds. Allostery — where binding at one subunit affects activity of another — is a hallmark of quaternary structure (hemoglobin's cooperative oxygen binding is the textbook example).
Key Facts
- The arrangement of multiple polypeptide subunits into a functional multi-chain complex.
- Not all peptides/proteins have quaternary structure — only those composed of more than one polypeptide chain.
- Classic examples: hemoglobin (α₂β₂ — four subunits carrying oxygen), antibodies (two heavy + two light chains linked by disulfide bonds), insulin hexamers (six insulin molecules + two zinc ions — the storage form in β-cell granules).
- Quaternary interactions are stabilized by the same non-covalent forces as tertiary structure plus inter-chain disulfide bonds.
- Allostery — where binding at one subunit affects activity of another — is a hallmark of quaternary structure (hemoglobin's cooperative oxygen binding is the textbook example).
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