Which component is part of the surface of lipoproteins?

• A. Apolipoprotein
• B. Phospholipids
• C. Non-esterified cholesterol
• D. Triglycerides

Answer: (A)

Lipoprotein particles have a surface layer formed by phospholipids and free cholesterol with apolipoproteins attached to that surface, while the core stores triglycerides and cholesteryl esters. The apolipoprotein is the protein component on the surface that provides structural stability and acts as a ligand for receptors and enzymes, giving the particle its identity in metabolic pathways. The triglycerides and cholesteryl esters reside in the center, not on the surface, and are the primary lipid stores. So, among these options, the apolipoprotein stands out as the surface component because it is the protein part exposed to the surrounding environment and critical for recognition by receptors.