Chapter 5: The Structure and Function of Large Biological Molecules

Overview: The Molecules of Life

All living organisms are composed of four major classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids. These molecules are essential for the structure, function, and regulation of the body's tissues and organs. When small organic molecules join together, they form larger, more complex molecules known as macromolecules.

• Macromolecule: A large molecule formed by the joining of smaller molecules, often complex in structure.

• Macromolecules are typically polymers, constructed from repeating units called monomers.

Macromolecules as Polymers

Three of the four classes of biological macromolecules—carbohydrates, proteins, and nucleic acids—are polymers. A polymer is a long molecule consisting of many similar or identical building blocks (monomers) linked by covalent bonds.

• Carbohydrates

• Proteins

• Nucleic acids

• Polymer: Long molecule made of monomers joined by covalent bonds.

Synthesis and Breakdown of Polymers

Polymers are formed and broken down by specific chemical reactions:

• Dehydration Synthesis (Condensation Reaction): Monomers are joined together by removing a molecule of water (), forming a covalent bond between them.

• Hydrolysis: Polymers are disassembled by adding a molecule of water, which breaks the covalent bond between monomers.

Example: Formation and breakdown of a polymer:

• Dehydration:

• Hydrolysis:

Diversity of Polymers

Each class of polymer is formed from a specific set of monomers. Despite a limited number of monomer types, the arrangement and sequence of these monomers create a vast diversity of polymers, giving rise to the unique molecular identity of each organism.

• Example: Different types of carbohydrates are formed from various arrangements of sugar monomers.

• Organisms share the same basic monomer types but differ in the sequence and structure of their polymers.

Carbohydrates

Types of Carbohydrates

Carbohydrates are organic molecules that include both simple sugars and their polymers. They serve as energy sources and structural components in cells.

• Monosaccharides: Single sugar molecules (e.g., glucose).

• Disaccharides: Two monosaccharides joined by dehydration synthesis (e.g., sucrose).

• Polysaccharides: Polymers composed of many monosaccharides linked together by dehydration synthesis (e.g., starch, cellulose).

Additional info: Carbohydrates generally have molecular formulas that are multiples of (e.g., glucose is ). Monosaccharides can be classified by the location of their carbonyl group (aldose or ketose) and the number of carbons in their skeleton.