​Given below are some components that could potentially influence membrane fluidity:

i. Monomeric G-proteins
ii. Peripheral membrane proteins
iii. Sphingolipids
iv. Phospholipid sidechain saturation
v. Cholesterol

Choose the option that has all the components that can influence membrane fluidity.

Correct option is C

Membrane fluidity refers to how easily lipids and proteins move within the lipid bilayer. Several factors influence membrane fluidity, including lipid composition, temperature, and cholesterol content.

i. Monomeric G-proteins

Incorrect – Does NOT influence membrane fluidity

• Monomeric G-proteins (e.g., Ras, Rab) are signaling molecules that associate with membranes but do not alter membrane structure or fluidity.
• Their activity affects cell signaling rather than membrane fluidity.

ii. Peripheral membrane proteins

Incorrect – Does NOT significantly influence membrane fluidity

• Peripheral proteins attach to the membrane surface without embedding into the bilayer.
• Since they do not disrupt lipid packing, they have minimal influence on membrane fluidity.

iii. Sphingolipids

Correct – Influences membrane fluidity

• Sphingolipids (e.g., sphingomyelin, glycosphingolipids) are major components of lipid rafts, which create rigid, less fluid membrane regions.
• High sphingolipid content reduces membrane fluidity by increasing lipid packing.

iv. Phospholipid sidechain saturation

Correct – Influences membrane fluidity

• Saturated phospholipids (no double bonds) reduce fluidity because they pack tightly.
• Unsaturated phospholipids (with double bonds) increase fluidity by preventing tight packing.
• This factor is crucial in regulating membrane flexibility in different temperature conditions.

v. Cholesterol

Correct – Influences membrane fluidity

• At high temperatures, cholesterol reduces fluidity by stabilizing the membrane.
• At low temperatures, cholesterol prevents solidification by disrupting lipid packing, maintaining fluidity.
• Overall, cholesterol acts as a fluidity buffer.

Information Booster:

Factors Affecting Membrane Fluidity:

1. Lipid Composition:

   • More saturated fatty acids → Less fluidity.
   • More unsaturated fatty acids → More fluidity.

2. Cholesterol:

   • Acts as a fluidity buffer, preventing extreme changes in membrane fluidity.

3. Temperature:

   • Higher temperatures → Increases fluidity.
   • Lower temperatures → Decreases fluidity.

4. Lipid Rafts (Sphingolipids & Cholesterol):

   • Create less fluid, more ordered membrane regions important for cell signaling.