Structure and Function of Large Biological Molecules

Chapter 5: The Structure and Function of Large Biological Molecules

Introduction

This chapter examines the structure and function of macromolecules that are essential to life. The four major classes of biological macromolecules—carbohydrates, lipids, proteins, and nucleic acids—are discussed in terms of their assembly, classification, and biological roles.

Macromolecules: Polymers and Monomers

Definition and Classification

• Macromolecules are large, complex molecules composed of thousands of covalently connected atoms.

• Most macromolecules are polymers, which are long chains made up of repeating subunits called monomers.

• The four main classes of macromolecules are:

  • Carbohydrates

  • Lipids

  • Proteins

  • Nucleic acids

Example: Starch is a polymer made of glucose monomers.

Polymerization and Depolymerization

• Polymerization is the process by which monomers are covalently bonded to form a polymer.

• This process often involves a dehydration reaction (also called condensation), where a water molecule is removed to form a new bond.

• Depolymerization (hydrolysis) is the reverse process, where water is added to break bonds between monomers.

Equation for Dehydration Synthesis:

$\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + \text{H}_2\text{O}$

Equation for Hydrolysis:

$\text{Polymer} + \text{H}_2\text{O} \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

Classification Table: Major Biological Macromolecules

Class	Monomer	Polymer	Main Functions
Carbohydrates	Monosaccharides	Polysaccharides	Energy storage, structural support
Lipids	Glycerol, fatty acids	Triglycerides, phospholipids, steroids	Energy storage, membrane structure, signaling
Proteins	Amino acids	Polypeptides	Catalysis, structure, transport, signaling
Nucleic acids	Nucleotides	DNA, RNA	Genetic information storage and transfer

Additional info: The above table summarizes the main types of macromolecules, their building blocks, and their primary biological functions. Lipids are not true polymers but are included due to their importance in biological systems.