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 to the structure and function of living organisms. These molecules are typically polymers, which are long chains composed 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.
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 monomers by the addition of water, essentially the reverse of a dehydration reaction. 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
The four major classes of biological molecules and their monomers are summarized below:
Class | Polymer | Monomer | Example |
|---|---|---|---|
Carbohydrates | Polysaccharide (e.g., starch) | Monosaccharide (e.g., glucose) | Starch, cellulose |
Proteins | Polypeptide | Amino acid | Enzymes, hemoglobin |
Nucleic Acids | Polynucleotide (e.g., DNA, RNA) | Nucleotide | DNA, RNA |
Lipids | Not a true polymer | Varies (e.g., fatty acids, glycerol) | Fats, phospholipids, steroids |
Key Points
Carbohydrates are polymers of sugars and serve as fuel and building material.
Proteins are polymers of amino acids and perform a wide range of functions, including catalysis, transport, and structural support.
Nucleic acids are polymers of nucleotides and store and transmit genetic information.
Lipids are a diverse group of hydrophobic molecules, important for energy storage, membrane structure, and signaling.
Examples and Applications
Starch (a carbohydrate) is a storage form of energy in plants.
Hemoglobin (a protein) transports oxygen in the blood.
DNA (a nucleic acid) encodes genetic information.
Phospholipids (a lipid) form the structural basis of cell membranes.
Additional info: The provided images and text are consistent with introductory material for a General Biology course, specifically focusing on the structure and function of macromolecules as covered in a typical college-level curriculum.
