Question

You have a planar bilayer with equal amounts of saturated and unsaturated phospholipids. After testing the permeability of this membrane to glucose, you increase the proportion of unsaturated phospholipids in the bilayer. What will happen to the membrane's permeability to glucose?

A) Permeability to glucose will increase.
B) Permeability to glucose will decrease.
C) Permeability to glucose will stay the same.
D) You cannot predict the outcome. You simply have to make the measurement.

Answer 1

Increasing the proportion of unsaturated phospholipids in a bilayer membrane results in increased permeability to glucose due to the enhanced fluidity from kinks in the unsaturated fatty acid tails.

Step-by-step explanation:

When the proportion of unsaturated phospholipids in the bilayer membrane increases, the membrane's permeability to glucose will likely increase. This occurs because unsaturated fatty acids have more kinks or bends due to the presence of C=C double bonds in their hydrocarbon chains.

These kinks push apart the phospholipid tails, making the membrane more fluid and allowing more space for molecules like glucose to pass through more easily. Saturated fatty acids, on the other hand, have straighter chains and pack together more tightly, making the membrane less permeable. Since the plasma membrane is impermeable to polar molecules without assistance, the increased fluidity with more unsaturated lipids provides greater opportunity for glucose to encounter and pass through transport proteins that facilitate its crossing.