Macromolecules: Structure and Function

Introduction to Macromolecules

Macromolecules are large, complex molecules essential to life, composed of thousands of atoms and often weighing over 100,000 daltons. The four major classes of macromolecules are carbohydrates, proteins, nucleic acids, and lipids. These molecules are fundamental to the structure and function of cells.

• Macromolecules: Large molecules formed by the joining of smaller organic molecules.

• Most macromolecules (except lipids) are polymers—long chains of repeating units called monomers.

• Monomers are small molecules that can join together to form polymers via covalent bonds.

• Some monomers also have independent biological functions.

Polymerization: Building and Breaking Polymers

The formation and breakdown of polymers involve specific chemical reactions that are similar across all classes of macromolecules.

• Dehydration (Condensation) Reaction: Monomers are joined together by covalent bonds through the removal of a water molecule. One monomer provides a hydroxyl group (–OH), and the other provides a hydrogen (–H), forming water () as a byproduct. This process requires energy and is catalyzed by enzymes.

• Hydrolysis: The reverse process, in which polymers are broken down into monomers by the addition of water. A hydrogen atom and a hydroxyl group from a water molecule attach to the sites where the covalent bond was broken. Hydrolysis is essential in digestion and is also enzyme-catalyzed.

Key Reactions

• Dehydration Synthesis:

• Hydrolysis:

Diversity of Biological Polymers

Cells can build thousands of different macromolecules from a small set of monomers. This diversity arises from the various combinations and sequences of about 40–50 common monomers (and some rarer ones), analogous to how the 26 letters of the alphabet can create a vast array of words.

• Biological molecules vary among cells of the same individual, more among unrelated individuals, and even more between species.

• The unique properties and functions of each macromolecule are determined by the specific sequence and arrangement of its monomers.

Summary Table: Key Features of Macromolecules

Examples and Applications

• Example of Dehydration Synthesis: Formation of a disaccharide from two monosaccharides (e.g., glucose + fructose → sucrose + water).

• Example of Hydrolysis: Digestion of starch into glucose monomers in the human digestive tract.

Additional info: The notes above are based on the introductory section of a General Biology textbook chapter on macromolecules, focusing on the general principles of polymer formation and diversity. Later sections would cover the specific classes (carbohydrates, proteins, nucleic acids, and lipids) in detail.