Distinguishing protein structures: collagen vs. haemoglobin

Steps:

• Recall collagen is a fibrous protein with triple helix secondary structure but no quaternary structure.
• Recall haemoglobin is a globular protein with quaternary structure from four polypeptide subunits.
• Examine choices: they compare presence of features (e.g., secondary structure in both, quaternary in haemoglobin only).
• Select row matching these: first feature shared, second unique to haemoglobin.

Why B is correct:

• Matches collagen having shared structural elements (e.g., helices) with haemoglobin, while haemoglobin alone has quaternary structure.

Why the others are wrong:

• A: Incorrectly attributes second feature to both proteins.
• C: Falsely limits first feature to haemoglobin only and second to both.
• D: Wrongly restricts both features to haemoglobin only.

Final answer: B