Membrane lipids in tissue samples obtained from different parts of the leg of a reindeer have different fatty acid compositions. Membrane lipids from tissue near the hooves contain a larger proportion of unsaturated fatty acids than those from tissue in the upper leg. What is the significance of this observation? Include a molecular-level explanation for the effects of the unsaturated fatty acids.

The presence of a larger proportion of unsaturated fatty acids in membranes imparts them fluidity at lower temperatures as required to maintain their normal functioning.

Explanation:

The proportion of unsaturated and saturated fatty acids in membranes regulates their fluidity. At lower temperatures, membranes become more rigid. To maintain their normal fluidity, the proportion of the unsaturated fatty acids in membranes is increased. The unsaturated fatty acids have double bonds in their hydrocarbon tails which in turn do not allow their tight packing and impart fluidity to the membrane core.

At higher temperatures, membranes become more fluid and therefore, the proportion of the unsaturated fatty acids is reduced. The tissues of reindeer at the body's extremities such as those near hooves are exposed to surroundings and thereby, lose heat and have lower temperatures. To maintain the fluidity of membranes, the cells of these tissues incorporate more of the unsaturated fatty acids in their membranes as compared to the tissues in the upper legs where the body temperature is relatively higher.