Final answer:
The lateral motion of proteins in a lipid bilayer is restricted by the composition of the bilayer and the presence of cholesterol. The correct option is a.
Step-by-step explanation:
The lateral motion of proteins in a lipid bilayer is restricted by the composition of the bilayer and the presence of cholesterol. Specifically, phospholipid composition and cholesterol content play a role in limiting the lateral movement of proteins.
Phospholipids are the main building blocks of the lipid bilayer, and their fatty acid tails interact through hydrophobic interactions.
This limits the movement of proteins as they are unable to freely pass through this hydrophobic interior. Additionally, cholesterol molecules fill the spaces between fatty acid tails, reducing the fluidity of the membrane and restricting the lateral motion of proteins. The correct option is a.