The Structure and Function of Large Biological Molecules

Chapter 5: The Structure and Function of Large Biological Molecules

Introduction

Large biological molecules, also known as macromolecules, are essential for life and perform a wide variety of functions in living organisms. This chapter explores the four major classes of biological molecules: carbohydrates, proteins, nucleic acids, and lipids. Understanding their structure and function is fundamental to the study of biology.

The Four Major Classes of Biological Molecules

Overview of Macromolecules

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

• Three of the four classes—carbohydrates, proteins, and nucleic acids—are polymers, which are long molecules built by linking together smaller units called monomers.

• Lipids are the fourth class; they are not true polymers or macromolecules but are grouped with them due to their biological importance.

Key Terms

• Monomer: A small molecule that can join together with other similar molecules to form a polymer.

• Polymer: A long molecule consisting of many similar or identical building blocks linked by covalent bonds.

Examples of Each Class

• Carbohydrates: Monomer = glucose; Polymer = starch

• Proteins: Monomer = amino acid; Polymer = protein (e.g., alcohol dehydrogenase)

• Nucleic Acids: Monomer = nucleotide; Polymer = DNA or RNA

• Lipids: Not polymers; example = phospholipid

Polymer Synthesis and Breakdown

Dehydration Synthesis (Condensation Reaction)

Polymers are synthesized by joining monomers through a process called dehydration synthesis or condensation reaction.

• During this reaction, a water molecule is removed as two monomers are covalently bonded together.

• This process is repeated to build long chains of polymers.

Equation:

$\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + H_2O$

Hydrolysis

Polymers can be broken down into monomers by the reverse process, called hydrolysis.

• Hydrolysis adds a water molecule, breaking the bond between monomers.

• This process is essential for digestion and recycling of biological molecules.

Equation:

$\text{Polymer} + H_2O \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

Summary Table: Polymer Formation and Breakdown

Process	Description	Water Involved
Dehydration Synthesis	Joins monomers to form a polymer	Water is removed
Hydrolysis	Breaks polymers into monomers	Water is added

Additional Resources

• For a visual explanation of dehydration synthesis and hydrolysis, see: Dehydration Synthesis and Hydrolysis Video

Summary

• Three major classes of biological molecules—carbohydrates, proteins, and nucleic acids—are polymers made from monomers.

• Lipids are not polymers but are crucial biological molecules.

• Dehydration synthesis builds polymers by removing water, while hydrolysis breaks them down by adding water.

Additional info: Further details on the specific structures and functions of each class (e.g., types of carbohydrates, protein structure levels, nucleic acid components, and lipid diversity) are typically covered in subsequent sections of this chapter.