Which of the following statements is TRUE of membrane phospholipids
a. The hydrophilic head groups face the interior portion of the membrane.
b. The hydrophobic tail groups face the exterior portion of the membrane.
c. They can easily flip-flop from one side of the membrane to the other.
d. They freely move laterally within the membrane.
e. They are non-polar.
The correct answer and explanation is :
Correct Answer: d. They freely move laterally within the membrane.
Explanation:
Phospholipids are a major component of cellular membranes and are arranged in a bilayer, giving the membrane its fluid and semi-permeable nature. Each phospholipid molecule is amphipathic, meaning it has both hydrophilic (water-loving) and hydrophobic (water-fearing) regions. The hydrophilic head is attracted to water and faces the aqueous environment both outside the cell and in the cytoplasm. The hydrophobic tails, made of fatty acid chains, face inward, away from water, interacting with one another in the interior of the membrane.
Option d, stating that phospholipids freely move laterally within the membrane, is true. This movement is part of what is described in the Fluid Mosaic Model of the membrane. Lateral movement allows phospholipids to diffuse side-to-side within the same layer of the bilayer, contributing to the membrane’s fluidity and flexibility. This is essential for various membrane functions such as vesicle formation, membrane protein mobility, and cell signaling.
Let’s briefly examine why the other options are incorrect:
- a. The hydrophilic head groups face the interior portion of the membrane – False. They face the aqueous environments outside the membrane and inside the cell (cytoplasm), not the interior hydrophobic region.
- b. The hydrophobic tail groups face the exterior portion of the membrane – False. They face inward, away from water, creating a hydrophobic core.
- c. They can easily flip-flop from one side of the membrane to the other – False. Flip-flop movement is rare because the hydrophilic head would have to pass through the hydrophobic core, which is energetically unfavorable.
- e. They are non-polar – False. Phospholipids have both polar (head) and non-polar (tail) regions.
Therefore, the true statement is d: They freely move laterally within the membrane. This lateral mobility supports the dynamic nature of the plasma membrane and is crucial for maintaining its integrity and function.