organic molecule
Summary
An organic molecule is a carbon-based compound, typically containing C–H bonds, with carbon bonded to H, O, N, S, or P. Biological macromolecules (carbohydrates, lipids, proteins, nucleic acids) are organic, and their behavior depends largely on their functional groups.
Detail
Meaning: Carbon forms four covalent bonds and bonds to itself in chains, branches, and rings, so it can build a huge variety of stable skeletons. Attached functional groups (hydroxyl, carbonyl, carboxyl, amino, phosphate) set the molecule's polarity, acidity or basicity, and reactivity. Polar and charged groups promote solubility in water, while long hydrocarbon regions are nonpolar and hydrophobic.
On the MCAT: Biochemistry passages ask you to sort structures into the four major classes of biomolecules, pick out functional groups, and predict properties from them. Typical questions: which group is ionized at physiological pH (a carboxyl group tends to lose H⁺, an amino group tends to gain it), whether a molecule dissolves in water or crosses a lipid membrane, and how monomers join into polymers by dehydration (condensation) and break apart by hydrolysis.
Common confusion: Organic does not mean natural, healthy, or made by living things. It is a statement about carbon-based structure. Not every carbon-containing species counts either: CO₂, carbonates, and cyanide are usually classed as inorganic. Water is essential to life but is inorganic. A quick test is to look for a carbon skeleton with C–H bonds.
Sources
- Lehninger Principles of Biochemistry
- Biochemistry (Berg, Tymoczko, Stryer)
- Organic Chemistry (Clayden)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.