If the temperature surrounding a cell increased, which of the following changes could help to keep the fluidity of the plasma membrane constant?
a. increasing the number of fatty acid tails in the membrane that contain double bonds
b. increasing the length of the fatty acid tails
c. both
d. neither
The correct answer and explanation is :
The correct answer is a. increasing the number of fatty acid tails in the membrane that contain double bonds.
Explanation:
The fluidity of the plasma membrane is crucial for the proper functioning of the cell. It is influenced by several factors, including temperature, the type of lipids in the membrane, and the fatty acid composition of phospholipids. Plasma membrane fluidity refers to the ability of the lipid molecules to move and diffuse within the bilayer. It must remain within an optimal range for the cell to function properly.
Temperature plays a key role in membrane fluidity. When the temperature increases, the molecules in the membrane gain more kinetic energy, which can cause the membrane to become too fluid. This excess fluidity can impair the integrity and function of the membrane, affecting processes like membrane trafficking, protein function, and signaling.
To counteract this effect and maintain membrane fluidity, the cell can alter the composition of its membrane lipids. The two primary factors that influence membrane fluidity are the length of the fatty acid tails and the degree of saturation (i.e., the number of double bonds) in those tails.
- Increasing the number of double bonds (unsaturation): Unsaturated fatty acids contain one or more double bonds between the carbon atoms in the fatty acid chain. These double bonds create “kinks” in the fatty acid tails, preventing them from packing tightly together. This results in increased fluidity of the membrane. In warm temperatures, the cell can increase the number of unsaturated fatty acids to prevent the membrane from becoming too rigid.
- Increasing the length of the fatty acid tails: Longer fatty acid tails tend to increase the hydrophobic interactions between the lipid molecules, making the membrane more rigid and less fluid. Therefore, increasing the length of fatty acid tails would not help maintain constant fluidity in response to higher temperatures.
Conclusion:
Increasing the number of double bonds (unsaturation) in the fatty acid tails of phospholipids allows the membrane to remain flexible and fluid, even as temperature rises, preventing excessive rigidity. This is why the correct answer is a.