cholesterol and membrane fluidity in animal cells

Question 1

What is the role of cholesterol in animal cell membranes?

Answer 1

Cholesterol makes up 20-40% of eukaryotic membrane lipids, stabilizing the membrane by regulating fluidity and structural integrity.

Question 2

How does cholesterol interact with the bilayer?

Answer 2

Cholesterol is amphipathic:

• Hydrophobic part inserts into the bilayer’s hydrophobic core.
• Hydrophilic -OH group faces outward, interacting with phosphate heads.

Question 3

Effect of cholesterol on membrane fluidity?

Answer 3

High temperatures:

• Cholesterol reduces fluidity, preventing the membrane from becoming too permeable.

Low temperatures:

• Prevents solidification by disrupting the packing of saturated fatty acids, maintaining flexibility.

Question 4

What is the ‘liquid-ordered’ phase?

Answer 4

Membranes are in a ‘liquid-ordered’ phase, where lipids are packed but fluid, allowing movement. Cholesterol ensures the membrane is stable and flexible.

Question 5

Why is membrane fluidity important?

Answer 5

Proper fluidity is vital for:

• Too fluid: Increased permeability.
• Too rigid: Restricted movement and potential rupture.
• Cholesterol keeps membranes at optimal fluidity for function and stability.