Chapter 5: Biological Macromolecules – Structure and Function

Macromolecules: The Molecules of Life

Overview of Biological Macromolecules

Biological macromolecules are large, complex molecules essential for life. Most are polymers, built from smaller subunits called monomers. The four major classes are carbohydrates, proteins, nucleic acids, and lipids. Each class has distinct structures and functions in cells.

• Carbohydrates: Serve as energy sources and provide structural support. Example: Glucose and starch.

• Proteins: Perform a wide range of functions, including catalyzing reactions (enzymes), transporting substances, and providing structural support. Example: Alcohol dehydrogenase.

• Nucleic acids: Store and transmit genetic information. Example: DNA and RNA.

• Lipids: Not true polymers or macromolecules; they are hydrophobic and serve as energy storage, components of cell membranes, and hormones. Example: Phospholipids.

Concept 5.1: Macromolecules Are Polymers Built from Monomers

Monomers and Polymerization

Most biological macromolecules are polymers, formed by linking together monomers through chemical reactions. This process is called polymerization.

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

• Polymer: A long molecule consisting of many monomers linked together.

• Polymerization: The process of joining monomers to form a polymer.

• Examples: Carbohydrates (monomer: monosaccharide), proteins (monomer: amino acid), nucleic acids (monomer: nucleotide).

Dehydration (Condensation) Reactions

Polymers are synthesized by dehydration reactions, also known as condensation reactions. In these reactions, a water molecule is removed to form a new covalent bond between monomers.

• Enzymes: Biological catalysts that speed up dehydration reactions.

• Dehydration Reaction: $\text{Monomer}_1 + \text{Monomer}_2 \xrightarrow{\text{Enzyme}} \text{Polymer} + H_2O$

• Result: Formation of longer polymers from shorter ones and monomers.

• Example: Formation of maltose from two glucose molecules.

Hydrolysis Reactions

Polymers are broken down into monomers by hydrolysis reactions. In hydrolysis, a water molecule is added, breaking the covalent bond between monomers.

• Hydrolysis: $\text{Polymer} + H_2O \xrightarrow{\text{Enzyme}} \text{Monomer}_1 + \text{Monomer}_2$

• Hydro-: Means water; -lysis: Means break.

• Result: Breakdown of polymers into their monomer components.

• Example: Digestion of starch into glucose monomers.

Classification of Biological Molecules

Carbohydrates

Carbohydrates are sugars and their polymers. They serve as fuel and building material for cells.

• Monosaccharides: Simple sugars (e.g., glucose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose).

• Functions: Energy storage (starch in plants, glycogen in animals), structural support (cellulose in plants).

Proteins

Proteins are polymers of amino acids and perform many cellular functions.

• Enzymes: Catalyze biochemical reactions.

• Transport: Move substances across cell membranes.

• Structure: Provide support and shape to cells and tissues.

Nucleic Acids

Nucleic acids are polymers of nucleotides and are responsible for storing and transmitting genetic information.

• DNA: Deoxyribonucleic acid; stores genetic instructions.

• RNA: Ribonucleic acid; involved in gene expression and protein synthesis.

Lipids

Lipids are a diverse group of hydrophobic molecules. Unlike other macromolecules, they are not polymers.

• Structure: Mostly hydrocarbons; do not mix well with water.

• Functions: Energy storage, cell membrane structure (phospholipids), hormones (steroids).

• Example: Phospholipids form the bilayer of cell membranes.

Summary Table: Major Classes of Biological Molecules

Class	Monomer	Polymer	Main Functions
Carbohydrates	Monosaccharide	Polysaccharide	Energy storage, structural support
Proteins	Amino acid	Polypeptide	Catalysis, transport, structure
Nucleic acids	Nucleotide	DNA/RNA	Genetic information storage and transmission
Lipids	None (not a true polymer)	None	Energy storage, membranes, hormones

Additional info: These notes expand on the brief points in the slides and images, providing definitions, examples, and context for each major class of biological macromolecules. Equations are given in LaTeX format for clarity.