Chemical Reactions

Chemical Reactions

Every living cell is a busy chemical factory: thousands of reactions run inside it every second - building large molecules from small ones, breaking food down for energy, and converting one compound into another. Left alone, most of these reactions would proceed far too slowly to keep an organism alive, because the reacting molecules first need a push of energy (called the activation energy) to get started, and at the mild temperatures inside a living body very few molecules have that much energy on their own.

A catalyst is a substance that lowers the amount of activation energy a reaction needs, so the reaction goes much faster, while the catalyst itself comes out of the reaction chemically unchanged and ready to be used again. Cells use their own biological catalysts, called enzymes, to make essential reactions happen quickly, in an organised sequence, and under the gentle conditions of temperature and pH found inside the body. Without enzymes, the chemistry that keeps a cell alive would simply be too slow to matter.