Question

Examine the model of cholic acid (Problem 2.65) and account for the ability of this and other bile salts to emulsify fats and oils and thus aid in their digestion.

Short answer

Answer: Cholic acid and other bile salts help emulsify fats and oils by using their amphiphilic properties to form micelles, which surround and disperse the fats in aqueous environments. This process makes it easier for digestive enzymes to break down the fat molecules, facilitating their digestion and absorption by the body.

Step-by-step solution

Understanding Cholic Acid Structure

First, let's understand the structure of cholic acid. Cholic acid is a bile salt, which is a major component of bile - a substance produced by the liver that aids in digestion. Cholic acid is a steroid molecule with a hydroxyl (OH), a carboxyl (COOH) group, and hydrocarbon chains connected to a steroid ring system.

Amphiphilic properties of cholic acid

The presence of hydroxyl (OH) and carboxyl (COOH) groups in cholic acid makes parts of the molecule polar, while the hydrocarbon chains and steroid ring system are nonpolar. This gives cholic acid amphiphilic properties, meaning it has both hydrophilic (water-loving) and hydrophobic (water-hating) parts. These properties are essential for bile salts to emulsify fats and oils.

Emulsification Process

Emulsification is the process of blending two immiscible substances, such as fats and water. The amphiphilic properties of bile salts, like cholic acid, allow them to interact with both fats (nonpolar) and water (polar). The hydrophobic part of the bile salt interacts with the hydrophobic part of the fat molecule, while the hydrophilic part interacts with the water.

Formation of Micelles

When bile salts like cholic acid are introduced to a mixture of fat and water, they effectively surround the fat droplets and form micelles. Micelles are spherical arrangements of amphiphilic molecules with the hydrophobic parts facing inwards, away from water, and the hydrophilic parts facing the aqueous environment. The formation of micelles reduces the surface area of the fat droplets and disperses them throughout the watery environment, making it easier for digestive enzymes (such as lipases) to break down the fat molecules into smaller components that can be absorbed by the body. In conclusion, cholic acid and other bile salts emulsify fats and oils by utilizing their amphiphilic properties to form micelles, which surround and disperse fats in aqueous environments. This process facilitates the digestion and absorption of fats in the body.