The Chemistry of Life

Carbon is the undisputed king of biological chemistry. With an atomic number of 6, carbon has an electron configuration of $1s^2 2s^2 2p^2$. This means it possesses 4 valence electrons in its outer shell. To achieve the stable 'octet' state, carbon must form four covalent bonds. This specific geometry allows carbon to serve as a 3D scaffold, creating straight chains, branched structures, and stable rings. Because carbon-carbon bonds are strong enough to be stable but flexible enough to be broken during metabolic processes, carbon provides the perfect balance for the dynamic chemistry of life.

Pure hydrocarbons (hydrogen and carbon) are non-polar and relatively unreactive. Life becomes interesting when functional groups—specific clusters of atoms—attach to the carbon skeleton.

1. Hydroxyl ($-OH$): Found in alcohols; makes molecules polar and water-soluble. 2. Carboxyl ($-COOH$): Acts as an acid because it can donate a proton ($H^+$). 3. Amino ($-NH_2$): Acts as a base by picking up $H^+$. 4. Phosphate ($-PO_4^{3-}$): Highly electronegative and essential for energy transfer in molecules like ATP.

Biological molecules are often macromolecules—giant chains called polymers made of repeating units called monomers.

To build a polymer, cells use dehydration synthesis. In this reaction, one monomer provides a hydroxyl group ($-OH$) and the other provides a hydrogen ($-H$), releasing a water molecule ($H_2O$) as a covalent bond forms between them. To break these chains down, cells perform hydrolysis (literally 'water-breaking'). By adding a water molecule back into the bond, the polymer is split into its original monomers.