Chapter 5: The Structure and Function of Large Biological Molecules

Overview of Biological Macromolecules

Large biological molecules, also known as macromolecules, are essential for the structure and function of living cells. The four major classes are carbohydrates, proteins, nucleic acids, and lipids. Except for lipids, these are polymers built from monomers.

• Carbohydrates: Serve as fuel and building material. Example: Starch (polymer of glucose).

• Proteins: Perform a wide range of functions, including catalysis, defense, transport, and structural support. Example: Alcohol dehydrogenase (enzyme).

• Nucleic acids: Store and transmit hereditary information. Example: DNA (polymer of nucleotides).

• Lipids: Diverse group of hydrophobic molecules, not true polymers. Example: Phospholipids (major component of cell membranes).

Macromolecules: Polymers and Monomers

Most macromolecules are polymers, which are long chains of repeating units called monomers. The diversity and complexity of life arise from the arrangement of these monomers into polymers.

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

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

• Major biological polymers: Carbohydrates, proteins, and nucleic acids.

Synthesis and Breakdown of Polymers

Polymers are assembled and disassembled by 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: Synthesizes a polymer by removing a water molecule, forming a new covalent bond between monomers.

• Hydrolysis: Breaks down a polymer by adding a water molecule, breaking the covalent bond between monomers.

Equations:

• Dehydration:

• Hydrolysis:

Diversity of Polymers

Cells contain thousands of different macromolecules, which vary among cells, species, and even more between different organisms. This diversity is possible because a huge variety of polymers can be built from a small set of monomers.

• Variation: Macromolecules differ among cells of an organism, more within a species, and even more between species.

• Basis of diversity: Arrangement and sequence of monomers.

Summary Table: Major Classes of Biological Molecules

Example: Dehydration and Hydrolysis Reactions

• Dehydration: Formation of maltose from two glucose molecules by removal of water.

• Hydrolysis: Breakdown of starch into glucose monomers by addition of water.

Additional info: These notes cover the introductory concepts of macromolecules, their classification, and the chemical processes involved in their synthesis and breakdown, as presented in a General Biology college course.