Question

the fluidity of cell membranes is highly regulated by cells such that some regions of the membrane may have very low fluidity while the rest of the cell membrane has higher fluidity. this is useful to the cell because it can help cluster together groups of proteins whose functions depend on one another. if the membrane is less fluid, the proteins cannot move as much laterally within the membrane and tend to stay close to one another. this can make functions like the transmission of signals from one brain cell to another much more efficient.
what changes in lipid composition would decrease the fluidity of a cell membrane? assume typical human body temperature. select all that apply.
□ decrease in the average length of lipid tails.
□ increase in the percentage of cholesterol.
□ increase in the percentage of saturated lipids.
□ increase in the average length of lipid tails.
□ increase in the percentage of unsaturated lipids.

Explanation:

• Increase in the percentage of cholesterol: Cholesterol can reduce membrane fluidity by filling gaps between phospholipids, especially at typical human body temperature.
• Increase in the percentage of saturated lipids: Saturated lipids have straight tails that pack closely together, reducing fluidity.
• Increase in the average length of lipid tails: Longer tails have more van der Waals interactions, making the membrane less fluid.

A decrease in lipid tail length (more space for movement) and an increase in unsaturated lipids (kinked tails prevent tight packing) would increase fluidity, so those options are incorrect.

Answer:

• B. Increase in the percentage of cholesterol.
• C. Increase in the percentage of saturated lipids.
• D. Increase in the average length of lipid tails.