The image shows two triacylglycerol molecules with different fatty acid chains. If these fatty acids were in a phospholipid molecule, which of the two would form the most fluid membrane?
The correct answer and explanation is:
To determine which fatty acid in a phospholipid would form the most fluid membrane, the key factors are the degree of saturation and the length of the fatty acid chains.
Unsaturated fatty acids contain one or more double bonds in their hydrocarbon chains. These double bonds create kinks or bends, preventing the fatty acid chains from packing tightly together. This loose packing increases membrane fluidity.
Saturated fatty acids have no double bonds, so their hydrocarbon chains are straight. These straight chains pack tightly, resulting in a more rigid and less fluid membrane.
Additionally, shorter fatty acid chains increase membrane fluidity because shorter chains have fewer van der Waals interactions, making the membrane less dense.
If the two triacylglycerol molecules in the image have fatty acids where one is more unsaturated (with double bonds) and the other is more saturated (with no or fewer double bonds), the one with the unsaturated fatty acid chains would create a more fluid membrane when incorporated into a phospholipid bilayer.
For example, a phospholipid containing oleic acid (an 18-carbon monounsaturated fatty acid) would increase membrane fluidity more than one containing stearic acid (an 18-carbon saturated fatty acid).
In summary, the triacylglycerol molecule with unsaturated fatty acid chains would form the most fluid membrane if those fatty acids were part of phospholipids. The presence of cis double bonds disrupts tight packing of the lipids, increasing the membrane’s fluidity, which is crucial for membrane function, flexibility, and permeability.