BackThe Structure and Function of Large Biological Molecules
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Large Biological Molecules
Introduction to Macromolecules
Large biological molecules, also known as macromolecules, are essential for life and are involved in a wide range of cellular functions. Most macromolecules are polymers, which are long chains made up of repeating subunits called monomers. The four major classes of biological macromolecules are carbohydrates, proteins, nucleic acids, and lipids (though lipids are not true polymers).
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.
Macromolecule: A very large molecule, such as a protein, nucleic acid, or polysaccharide, with a molecular weight in the thousands or millions.
Carbohydrates, proteins, and nucleic acids are true polymers, while lipids are large molecules that do not form polymers.
Synthesis and Breakdown of Polymers
Dehydration and Hydrolysis Reactions
The formation and breakdown of polymers involve two key types of chemical reactions: dehydration reactions and hydrolysis.
Dehydration Reaction: A chemical reaction in which two monomers are covalently bonded to each other with the removal of a water molecule. This process builds polymers from monomers.
Hydrolysis: A chemical reaction that breaks bonds between two monomers by the addition of a water molecule. This process disassembles polymers into monomers.
Enzymes are specialized macromolecules (usually proteins) that speed up chemical reactions, including those that make or break down polymers.
Dehydration Reaction Example
When a short polymer and an unlinked monomer join, a water molecule is released, forming a longer polymer.
General equation:
Hydrolysis Reaction Example
When a polymer is broken down, a water molecule is added, breaking the bond and releasing monomers.
General equation:
Classes of Biological Macromolecules
Overview Table
Class | Monomer (Building Block) | Polymer (Macromolecule) | Example |
|---|---|---|---|
Carbohydrates | Monosaccharide | Polysaccharide | Starch, Cellulose |
Proteins | Amino acid | Polypeptide/Protein | Enzymes, Hemoglobin |
Nucleic acids | Nucleotide | Polynucleotide (DNA/RNA) | DNA, RNA |
Lipids | Fatty acids, Glycerol | Not true polymers | Fats, Phospholipids, Steroids |
Additional info: Lipids are grouped with macromolecules due to their large size and biological importance, but they do not consist of repeating monomer units like true polymers.
Summary
Three classes of macromolecules—carbohydrates, proteins, and nucleic acids—are polymers built from monomers.
Lipids are large biological molecules that are not polymers but are essential for cell structure and function.
Enzymes catalyze the synthesis (dehydration) and breakdown (hydrolysis) of polymers.
