Question

Which of the following is true of amphipathic molecules? (A) \(\quad\) They form protective spheres in any solvent, with hydrophobic molecules interior and hydrophilic molecules exterior. (B) \(\quad\) They have two fatty acid chains and a polar head group. (C) \(\quad\) They are important to the formation of the phospholipid bilayer and soap bubbles. (D) \(\quad\) They have a glycerol base.

Short answer

Option (C) is true.

Step-by-step solution

Understand the Definition of Amphipathic Molecules

Amphipathic molecules have both hydrophilic (water-loving) and hydrophobic (water-fearing) parts. This dual characteristic is crucial for their function in biological structures and other applications.

Recognize Their Role in Structures

Amphipathic molecules are key components in the formation of structures like the phospholipid bilayer of cell membranes and soap bubbles. Their hydrophilic heads face water while their hydrophobic tails avoid it.

Evaluate Each Option

Let's examine each option to see which correctly describes amphipathic molecules:(A) Incorrect: Amphipathic molecules specifically form spheres called micelles in water environments, not in any solvent.(B) Incorrect: Having two fatty acid chains and a polar head group describe phospholipids specifically, but not all amphipathic molecules.(C) Correct: Amphipathic molecules are indeed important to the formation of phospholipid bilayers (cell membranes) and soap bubbles.(D) Incorrect: Not all amphipathic molecules have a glycerol base. This is true for triglycerides, not all amphipathic molecules.

Conclusion

After evaluating the options, the statement that correctly describes amphipathic molecules is option (C).

Key concepts

Phospholipid Bilayer

The phospholipid bilayer is an essential structure in cell membranes. It consists of two layers of phospholipid molecules, arranged so that their hydrophilic (water-attracting) heads face outward toward the water inside and outside the cell, and their hydrophobic (water-repelling) tails face inward, away from water. This formation creates a stable barrier between the cell and its external environment, which is crucial for protecting the cell's internal components.
Phospholipids, the main molecules in the bilayer, are amphipathic, meaning they have both hydrophilic and hydrophobic regions. This unique characteristic allows them to form bilayers in aqueous environments automatically, making them ideal for natural cell membrane construction.

Cell Membrane Structure

The cell membrane, often referred to as the plasma membrane, is a vital component of all living cells. It is primarily composed of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.
Besides providing structural support and shape to the cell, the cell membrane controls the movement of substances in and out of the cell. The amphipathic nature of phospholipids in the bilayer ensures that only certain molecules can diffuse through freely, while others require special protein channels or carriers.
This selective permeability is critical for maintaining homeostasis, allowing cells to communicate and perform necessary functions efficiently.

Soap Bubbles

Soap bubbles are a fun and illustrative example of amphipathic molecules in action. Soap molecules have hydrophilic heads and hydrophobic tails, making them amphipathic. When soap is added to water and agitated, the molecules arrange themselves into spheres called micelles, with the hydrophobic tails protected inside and the hydrophilic heads facing outward.
The surface of a soap bubble is essentially a thin film of water sandwiched between two layers of soap molecules. This setup lowers the surface tension of water, allowing the bubble to form and maintain its shape. Soap bubbles demonstrate how amphipathic molecules can self-organize to create stable structures even in environments that would otherwise be disruptive.

Hydrophilic and Hydrophobic Properties

Understanding hydrophilic and hydrophobic properties is fundamental to grasping the behavior of amphipathic molecules. Hydrophilic substances are attracted to water and can dissolve or interact well with it due to their polar nature. On the other hand, hydrophobic substances repel water and tend not to dissolve. They usually interact better with non-polar substances.
Amphipathic molecules, like phospholipids and soap molecules, contain both hydrophilic and hydrophobic regions. This dual nature allows them to play unique roles in various biological and chemical processes, such as forming cell membranes and creating micelles. These properties are key to their ability to spontaneously organize into structures that protect the hydrophobic regions from water while engaging the hydrophilic regions with it.