BackThe Structure and Function of Large Biological Molecules
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The Molecules of Life
Classes of Large Biological Molecules
All living organisms are composed of four major classes of large biological molecules, each with unique properties and functions essential for life.
Carbohydrates
Lipids
Proteins
Nucleic acids
Macromolecules are large, complex molecules whose unique properties arise from the specific arrangement of their atoms.
Carbon: The Basis of Molecular Diversity
Properties of Carbon
Carbon is fundamental to the molecular diversity of life due to its versatile bonding capabilities.
Carbon atoms can form four covalent bonds by sharing electrons.
Carbon skeletons can be straight, branched, or arranged in rings, allowing for a wide variety of molecular structures.
Organic compounds are molecules based on carbon bonded to other carbons and atoms of other elements.
Functional Groups in Biological Molecules
Role of Functional Groups
The unique properties of organic compounds depend on the size and shape of their carbon skeletons and the chemical groups attached to them. Functional groups are specific groups of atoms that confer characteristic chemical behaviors to molecules.
Functional groups affect a molecule’s function in a predictable way.
Important Chemical Groups of Organic Compounds
Chemical Group | Examples |
|---|---|
Hydroxyl group (-OH) | Alcohols (e.g., ethanol) |
Carbonyl group (C=O) | Aldehydes (e.g., formaldehyde), Ketones (e.g., acetone) |
Carboxyl group (-COOH) | Carboxylic acids (e.g., acetic acid), Ionized forms |
Amino group (-NH2) | Amines (e.g., glycine), Ionized forms |
Phosphate group (-OPO32-) | Organic phosphates (e.g., ATP) |
Methyl group (-CH3) | Methylated compounds |
Macromolecules: Polymers and Monomers
Polymer Formation
Most biological macromolecules are polymers, which are long chains made from repeating units called monomers. Three of the four major classes—carbohydrates, proteins, and nucleic acids—are 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.
Polymerization Reactions
Dehydration Reaction: Synthesizes polymers by removing a water molecule, forming a new bond between monomers.
Hydrolysis: Breaks down polymers by adding a water molecule, breaking the bond between monomers.
The Diversity of Polymers
Variation Among Macromolecules
Cells contain thousands of different macromolecules, which vary among cells, species, and even more between species. This diversity arises from a small set of monomers arranged in countless ways.
Macromolecules are highly variable and contribute to the complexity of life.
Structural variation is possible due to the flexibility of carbon skeletons and the presence of isomers.
Isomers: Structural Diversity
Definition and Importance
Compounds with the same molecular formula but different structural arrangements are called isomers. Isomers contribute to the molecular diversity of life by allowing different chemical properties and biological functions.
Structural isomers: Differ in the covalent arrangement of atoms.
Cis-trans isomers: Differ in spatial arrangement due to inflexible double bonds.
Enantiomers: Mirror-image isomers important in biology (e.g., amino acids).
Additional info: Isomerism is crucial in biochemistry, as different isomers can have dramatically different biological activities.
