Question

The hydrophobic effect is one of the most important noncovalent forces directing the self-assembly of biomolecules in aqueous solution. The hydrophobic effect arises from tendencies of biomolecules (1) to arrange polar groups so that they interact with the aqueous environment by hydrogen bonding and (2) to arrange nonpolar groups so that they are shielded from the aqueous environment. Show how the hydrophobic effect is involved in directing the following. (a) The formation of micelles by soaps and detergents (b) The formation of lipid bilayers by phospholipids

Short answer

Question: Explain the role of the hydrophobic effect in the self-assembly of biomolecules in aqueous solutions, specifically in the formation of micelles by soaps and detergents and the formation of lipid bilayers by phospholipids. Answer: The hydrophobic effect is a noncovalent force that affects how biomolecules arrange themselves in aqueous solutions. It is crucial in the self-assembly of amphiphilic molecules, such as soaps and detergents, and phospholipids. The hydrophobic effect guides the arrangement of these molecules, keeping their hydrophobic parts away from water. In the case of soaps and detergents, they form micelles where hydrophobic tails are tucked inside and hydrophilic heads face the water. For phospholipids, they commonly form lipid bilayers with hydrophilic heads facing the aqueous environment and hydrophobic tails facing each other, creating stable structures like the cell membrane.

Step-by-step solution

Understanding the hydrophobic effect

The hydrophobic effect is a noncovalent force that affects how biomolecules arrange themselves in aqueous solutions. It's a result of (1) polar groups forming hydrogen bonds with the surrounding water molecules and (2) nonpolar groups arranging themselves to minimize the interaction with the aqueous environment. The hydrophobic effect is crucial in understanding the self-assembly of biomolecules.

Formation of micelles by soaps and detergents

Soaps and detergents are amphiphilic molecules, meaning they have both hydrophilic (polar) and hydrophobic (nonpolar) parts. The hydrophilic part is usually an ionic head group that readily interacts with water, while the hydrophobic part is a long hydrocarbon tail that doesn't interact well with water. When these molecules are in aqueous solutions, they arrange themselves in such a way to minimize their unfavorable interaction with water, resulting in a formation called a micelle. The hydrophobic tails are tucked inside the micelle, away from the water, while the hydrophilic heads face the outside, interacting with the water molecules. The hydrophobic effect plays a crucial role in directing this arrangement in an aqueous environment.

Formation of lipid bilayers by phospholipids

Phospholipids, like soaps and detergents, are also amphiphilic molecules. They have a hydrophilic head (polar) and a hydrophobic tail (nonpolar). Although they can form micelles, they more commonly form lipid bilayers due to their different head and tail sizes. The lipid bilayers are formed by arranging the phospholipids in two opposing layers, with the hydrophilic heads facing the aqueous environment and the hydrophobic tails facing each other, thus shielding them from the water. This arrangement allows the formation of a stable, closed structure like the cell membrane of biological cells. The hydrophobic effect guides the arrangement of the phospholipids and promotes the formation of lipid bilayers in an aqueous environment.