The Chemical Basis of Life: Organic Molecules and Macromolecules

Organic molecule

A molecule that contains carbon (and often hydrogen) and is the basis of organic chemistry, especially those associated with life.

Inorganic molecule

A molecule that does not contain carbon-hydrogen bonds typical of organic molecules.

Macromolecule

A large, complex organic molecule built from many similar or repeating monomer units; examples include carbohydrates, lipids, proteins, and nucleic acids.

Carbon

Element with 4 electrons in its outer shell, allowing up to four covalent bonds; central to organic chemistry.

Covalent bond

A bond formed by sharing electrons between atoms.

Valence (bond capacity)

The number of electrons an atom needs to complete its outer shell, often determining how many covalent bonds it forms (e.g., carbon can form up to four).

Nonpolar covalent bond

A covalent bond where electrons are shared equally, resulting in no partial charges; typically found in hydrocarbons.

Polar covalent bond

A covalent bond where electrons are shared unequally, creating partial charges and often increasing solubility in water.

Hydrocarbon

Organic molecule composed mainly of carbon and hydrogen; typically nonpolar and hydrophobic.

Functional group

A group of atoms with characteristic chemical features that determine the reactivity of a molecule.

Hydroxyl group

–OH group; polar, common in alcohols and carbohydrates.

Carbonyl group

C=O group; found in aldehydes and ketones.

Carboxyl group

–COOH group; acidic; common in organic acids and amino acids.

Amino group

–NH2 group; basic; found in amino acids and many biomolecules.

Sulfhydryl group

–SH group; can form disulfide bridges in proteins, stabilizing structure.

Phosphate group

–OPO3^2− group; important in energy transfer and nucleic acids.

Methyl group

–CH3 group; nonpolar; can influence molecule activity and solubility.

Isomer

Molecules with the same molecular formula but different structures.

Structural isomer

Isomers that differ in the covalent arrangement of atoms.

Stereoisomer

Isomers with the same covalent bonds but different spatial arrangement.

Enantiomer

A pair of non-superimposable mirror-image isomers.

Monomer

A small building block that can join with others to form a polymer.

Polymer

A large molecule composed of repeating monomer units linked together.

Condensation (dehydration) reaction

A reaction that links monomers, releasing a molecule of water and forming a bond.

Hydrolysis

A reaction that breaks polymers into monomers by adding water; catalyzed by enzymes.

Carbohydrate

Macromolecule class made of C, H, O; includes sugars and their polymers; formula roughly Cn(H2O)n.

Monosaccharide

Simple sugar; basic unit of carbohydrates (e.g., glucose); pentose or hexose.

Pentose

Five-carbon monosaccharide.

Hexose

Six-carbon monosaccharide (e.g., glucose).

Glucose

Common hexose; primary blood sugar used by cells for energy.

Disaccharide

Carbohydrate composed of two monosaccharides joined by a glycosidic bond.

Glycosidic bond

Bond linking the sugar units in carbohydrates.

Polysaccharide

Carbohydrate polymer composed of many monosaccharide units; serves storage or structural roles.

Starch

Plant storage polysaccharide of glucose with α-1,4 and α-1,6 linkages forming branched chains.

Glycogen

Animal storage polysaccharide; highly branched glucose polymer.

Cellulose

Structural polysaccharide in plants with β-1,4 linkages; linear and rigid.

Chitin

Structural polysaccharide in arthropods and fungi; contains N-acetylglucosamine.

Lipid

Diverse group of hydrophobic molecules; nonpolar; includes fats, phospholipids, steroids, waxes.

Fat (triglyceride)

Glycerol backbone with three fatty acids; main form of energy storage in animals.

Fatty acid

Carboxyl-containing hydrocarbon chain; components of fats and phospholipids.

Saturated fat

Fat with no C=C bonds; typically solid at room temperature.

Unsaturated fat

Fat with one or more C=C bonds; typically liquid at room temperature; cis configuration common.

Trans fat

Hydrogenated unsaturated fats with trans double bonds; associated with health risks.

Phospholipid

Lipid with two fatty acids, a glycerol backbone, and a phosphate group; amphipathic and forms membranes.

Amphipathic

Molecule with both hydrophobic (nonpolar) and hydrophilic (polar) regions.

Steroid

Lipid with four fused carbon rings; hydrophobic; includes cholesterol and hormones.

Cholesterol

Steroid lipid important for membrane structure and precursor to steroid hormones.

Protein

Macromolecule with diverse functions; built from amino acids; structure dictates function.

Amino acid

Amino group, carboxyl group, central carbon (α-carbon), and variable R group; monomer of proteins.

Peptide bond

Covalent bond between the carboxyl of one amino acid and the amino of the next.

Polypeptide

Long chain of amino acids; folds to form a protein.

Primary structure

Linear sequence of amino acids in a polypeptide; held by peptide bonds.

Secondary structure

Local folding patterns (α-helix, β-pleated sheet) stabilized by hydrogen bonds.

Tertiary structure

Three-dimensional