Biomolecules with multiple C=O double bonds in structures

Steps:

• Saturated fatty acids consist of a hydrocarbon chain with only single bonds and one C=O double bond in the carboxyl group.
• Collagen is a fibrous protein with thousands of peptide bonds, each containing a C=O double bond.
• Haemoglobin is a protein with multiple subunits and hundreds of peptide bonds, plus heme groups featuring conjugated C=C double bonds.
• Only collagen and haemoglobin exceed two double bonds total.

Why C is correct:

• Proteins like collagen and haemoglobin contain numerous peptide bonds, each with a C=O double bond per definition of amide linkages, ensuring at least two.

Why the others are wrong:

• A includes saturated fatty acid, limited to one C=O double bond.
• B omits haemoglobin, which has multiple double bonds from peptides and heme.
• D includes saturated fatty acid (one double bond) and excludes collagen.

Final answer: C