GRE Subject Test: Biology : Understanding Membrane Structure

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #1 : Cell Membrane And Cell Wall

Which of the following conditions would result in a more fluid membrane?

Possible Answers:

Fully saturated fatty acid tails

A membrane in cold temperatures

Fatty acid tails with double bonds

Long fatty acid tails

Correct answer:

Fatty acid tails with double bonds

Explanation:

There are many factors that determine the fluidity of cell membranes. Membranes that are composed of fully saturated, long fatty acid tails are generally less fluid then the opposite conditions. In addition, lower temperatures result in a less fluid membrane.

Membranes that have fatty acid tails with double bonds are more fluid because the double bonds make it difficult for multiple phospholipids to float next to one another. The shape of the double bond adds a another dimension to the lipid, preventing the tails from packing together. Unsaturated fatty acids are thus more fluid than saturated fatty acids.

Example Question #2 : Cell Membrane And Cell Wall

Which of the following factors would you expect to see in a cell membrane for an animal living in a very hot environment?

Possible Answers:

Longer fatty acid tails

Reduced integral proteins

More unsaturated fatty acid tails

Reduced presence of cholesterol

Correct answer:

Longer fatty acid tails

Explanation:

In higher temperatures, the cell membrane is going to become increasingly fluid due to the increased movement of the phospholipids. The cell membrane can control its fluidity in high temperatures by both increasing the saturated fatty acid tail content of the phospholipids, as well as making the fatty acid tails longer. Cholesterol can also help by acting as a buffer at high temperatures.

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