Principles of Life for the AP Course (2nd Edition)

Published by W. J. Freeman
ISBN 10: 1464156417
ISBN 13: 978-1-46415-641-0

Chapter 5 - Section 5.1 - Biological Membranes Have a Common Structure and Are Fluid - Apply The Concept - Page 84: 1


In the first condition because there is no alteration to the membrane this is the control group. All other times can be compared to this time (of 65 seconds) to determine if the rate for diffusion of the fluorescent tag is "slow" or "fast." In the second condition in which the fatty acid chains are shortened, the rate of diffusion is quicker because the bilayer is shorter so the molecule has less length to travel across the membrane. In the third condition in which there are more cholesterol molecules that are added the rate of diffusion is longer. This is because cholesterol pulls lipid molecules tighter together therefore, diffusion will take more time. In the forth condition, the fatty acids have an increased number of unsaturated bonds. This causes "kinks" in the tails of the phospholipid which increases membrane fluidity so molecules can diffuse more easily/more quickly. In the fifth condition, proteins are large, bulky molecules. Based on the data that shows membrane diffusion is the slowest in this condition, it is likely that the protein that was added to the membrane is one that does not permit the passage of the fluorescent molecule and the protein is simply blocking molecule movement as the protein is a larger molecule than the phospholipids.

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