Chapter 5.1

Introduction to Biological Macromolecules

Biological macromolecules are large, complex molecules that are fundamental to the structure and function of living organisms. There are four major classes of biological molecules: carbohydrates, proteins, nucleic acids, and lipids. Three of these classes—carbohydrates, proteins, and nucleic acids—are polymers, while lipids are not true polymers.

• Carbohydrates: Serve as energy sources and structural materials.

• Proteins: Perform a wide range of functions, including catalysis, structure, and transport.

• Nucleic acids: Store and transmit genetic information.

• Lipids: Important for energy storage, membrane structure, and signaling.

Polymers and Monomers

Most biological macromolecules are polymers, which are long molecules made up of repeating subunits called monomers. The diversity of life is largely due to the variety of polymers that can be constructed from a small set of monomers.

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

• Monomer: The repeating unit that serves as the building block of a polymer.

• Examples:

  • Carbohydrates: Monomer = monosaccharide (e.g., glucose)

  • Proteins: Monomer = amino acid

  • Nucleic acids: Monomer = nucleotide

Synthesis and Breakdown of Polymers

The formation and breakdown of polymers involve specific chemical reactions, often catalyzed by enzymes.

• Enzymes: Specialized macromolecules that speed up chemical reactions, including those that build or break down polymers.

• Dehydration Reaction (Condensation Reaction):

  • Joins two monomers by removing a water molecule.

  • One monomer provides a hydroxyl group (–OH), and the other provides a hydrogen (–H).

  • Results in the formation of a covalent bond between monomers.

• Hydrolysis:

  • Breaks a covalent bond between monomers by adding a water molecule.

  • Essentially the reverse of a dehydration reaction.

Equation for Dehydration Reaction:

Equation for Hydrolysis:

Overview of the Four Major Classes of Biological Molecules

Key Terms and Definitions

• Macromolecule: A giant molecule formed by the joining of smaller molecules, usually by a condensation (dehydration) reaction.

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

• Monomer: The subunit that serves as the building block of a polymer.

• Enzyme: A macromolecule serving as a catalyst, a chemical agent that increases the rate of a reaction without being consumed.

• Dehydration reaction: A chemical reaction in which two molecules become covalently bonded to each other with the removal of a water molecule.

• Hydrolysis: A chemical reaction that breaks bonds between two molecules by the addition of water.

Examples and Applications

• Carbohydrates: Starch in plants stores energy; cellulose provides structural support in plant cell walls.

• Proteins: Enzymes catalyze biochemical reactions; structural proteins provide support (e.g., collagen).

• Nucleic acids: DNA stores genetic information; RNA is involved in protein synthesis.

• Lipids: Phospholipids form the basic structure of cell membranes; fats store energy.

Additional info: The images provided illustrate the molecular structure of macromolecules, the relationship between monomers and polymers, and the four major classes of biological molecules. The notes are based on content from a standard college-level biology textbook (e.g., Campbell Biology).