Carbonyl double bonds in biomolecular structures

Steps:

• Recall that double bonds here refer to C=O in linkages like esters and peptides.
• Triglycerides form from one glycerol and three fatty acids via three ester bonds, each with one C=O double bond, totaling three.
• Haemoglobin is a protein with ~574 amino acids across four chains, forming hundreds of peptide bonds, each with a C=O double bond.
• Collagen features long triple-helical chains with ~1000 amino acids per chain, yielding thousands of peptide bonds, each with a C=O double bond.

Why C is correct:

• Large proteins like haemoglobin and collagen have extensive polypeptide chains with far more than four peptide bonds, each containing a C=O double bond per definition of peptide linkage.

Why the others are wrong:

• A: Includes triglyceride, which has only three C=O double bonds.
• B: Includes triglyceride, which has only three C=O double bonds.
• D: Includes triglyceride, which has only three C=O double bonds.

Final answer: C