Which of the following molecules add stiffness and strength to the plasma membrane?

• A. Phosphatidylcholine
• B. Actin
• C. Cholesterol
• D. Glycogen

Answer: (C)

Verified step by step guidance

1. Understand the structure and function of the plasma membrane: The plasma membrane is a phospholipid bilayer that provides a flexible barrier for the cell. It contains various molecules, including lipids, proteins, and carbohydrates, which contribute to its properties.
2. Identify the role of cholesterol in the plasma membrane: Cholesterol is a lipid molecule that integrates into the phospholipid bilayer. It interacts with the fatty acid tails of phospholipids, reducing their movement and increasing membrane stiffness and strength.
3. Eliminate incorrect options: Phosphatidylcholine is a type of phospholipid that forms part of the bilayer but does not specifically add stiffness. Actin is a cytoskeletal protein that provides structural support inside the cell, not within the membrane. Glycogen is a carbohydrate used for energy storage and is not involved in membrane structure.
4. Conclude that cholesterol is the correct answer: Cholesterol's unique structure allows it to modulate membrane fluidity and provide mechanical stability, making it essential for maintaining the integrity of the plasma membrane.
5. Summarize the key concept: Cholesterol is the molecule that adds stiffness and strength to the plasma membrane by interacting with phospholipids and reducing their mobility.