BackBiological Macromolecules: The Four Major Classes of Organic Molecules
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Biological Macromolecules
Introduction to the Four Major Classes
Living organisms are composed of four main classes of organic molecules, also known as biological macromolecules. These are carbohydrates, lipids, proteins, and nucleic acids. Each class has unique structures, subunits, and functions essential for life.
Carbohydrates (e.g., starch)
Lipids (e.g., triacylglycerol, phospholipids)
Proteins (e.g., enzymes)
Nucleic acids (e.g., DNA, RNA)
Concept 5.1: Properties of Organic Molecules
Structure and Polymerization
Most biological macromolecules are polymers, which are long chains of repeating subunits called monomers. The exception is lipids, which are not true polymers.
Carbon skeletons form the backbone of organic molecules.
Side chains (functional groups) determine chemical reactivity and properties.
Polymers are formed by linking monomers through covalent bonds.
Examples of monomer-polymer relationships:
Sugar → Polysaccharide (Carbohydrate)
Amino acid → Protein
Nucleotide → Nucleic acid
Polymerization and Depolymerization
Dehydration Synthesis and Hydrolysis
Polymers are assembled and disassembled by two key chemical reactions:
Dehydration (Condensation) Synthesis: Monomers are joined by covalent bonds through the removal of a water molecule. This process builds polymers.
Hydrolysis: Polymers are broken down into monomers by the addition of water, breaking covalent bonds.
General equation for dehydration synthesis:
General equation for hydrolysis:
Study Chart: Major Classes of Biological Molecules
Class | Basic Subunit(s) | Complex Molecule | Functions | Examples |
|---|---|---|---|---|
Carbohydrates | Monosaccharide (e.g., glucose) | Polysaccharide (e.g., starch, cellulose) | Energy storage, structural support | Starch, glycogen, cellulose |
Lipids | Glycerol and fatty acids | Triglyceride, phospholipid, steroid | Energy storage, membrane structure, signaling | Fats, oils, phospholipids, cholesterol |
Nucleic acids | Nucleotide | DNA, RNA | Store and transmit genetic information | DNA, RNA |
Proteins | Amino acid | Polypeptide (protein) | Catalysis, structure, transport, signaling | Enzymes, antibodies, hemoglobin |
Summary Table: Monomers and Polymers
Subunit (Monomer) | Macromolecule (Polymer) |
|---|---|
Sugar | Polysaccharide |
Amino acid | Protein |
Nucleotide | Nucleic acid |
Key Points and Examples
Carbohydrates are composed of monosaccharides and serve as energy sources and structural materials.
Lipids are diverse hydrophobic molecules, including fats, phospholipids, and steroids. They are not true polymers.
Proteins are polymers of amino acids and perform a wide range of functions, including catalysis (enzymes), structure, and signaling.
Nucleic acids (DNA and RNA) are polymers of nucleotides and store genetic information.
Example: Polymerization
During the formation of a protein, amino acids are joined by peptide bonds through dehydration synthesis, resulting in a polypeptide chain.
Additional info:
Lipids, while not true polymers, are essential for membrane structure and energy storage.
Functional groups (e.g., hydroxyl, carboxyl, amino, phosphate) attached to carbon skeletons determine the chemical properties of macromolecules.
