Membrane Biochemistry — MCQs

Question 91: Which of the following is the primary component of the plasma membrane?

• A. Lipids
• B. Carbohydrates
• C. Proteins
• D. Phospholipids (Correct Answer)

Explanation: ***Phospholipids*** - **Phospholipids** form the fundamental **bilayer structure** of the plasma membrane, providing its selective permeability. - Their **amphipathic nature** (hydrophilic head and hydrophobic tail) allows for the spontaneous formation of this barrier in an aqueous environment. - Phospholipids constitute approximately **50% of membrane mass** and form the essential structural framework. *Lipids* - While phospholipids are indeed lipids, this option is **too general and imprecise** for the question asking about the "primary component." - The term "lipids" encompasses phospholipids, cholesterol (~20% of membrane lipids), and glycolipids, but only **phospholipids form the bilayer structure** itself. - Other lipids like **cholesterol** are present but act more as membrane fluidity regulators than primary structural elements. *Proteins* - While integral to membrane function, **proteins** are diverse in their roles (e.g., transport, receptors) but do not constitute the primary structural component of the bilayer. - They are embedded within or associated with the lipid bilayer, which itself provides the main framework. - Proteins account for variable percentages of membrane mass depending on membrane type but don't form the structural foundation. *Carbohydrates* - **Carbohydrates** are predominantly found on the **outer surface** of the plasma membrane, forming the glycocalyx. - Their main roles include **cell recognition** and adhesion, not forming the basic structural bilayer. - Carbohydrates constitute only **2-10%** of membrane mass in the form of glycoproteins and glycolipids.