enzymes

An intact onion does nothing to your eyes. But cutting one releases enzymes that act on sulfur compounds, triggering a chemical cascade that produces syn-propanethial-S-oxide — a volatile gas that irritates your cornea and forces your eyes to water. The science behind this everyday kitchen reaction reveals how plants weaponize chemistry as a defense mechanism.

Fireflies generate light without heat through a chemical reaction that achieves 41% efficiency — nearly three times more efficient than an incandescent bulb — powered entirely by ATP and oxygen.

Alcohol is absorbed into the bloodstream within minutes of consumption, but the liver metabolizes it at a nearly constant rate of about one standard drink per hour, a rate that cannot be accelerated by food or hydration. The body treats ethanol as a toxin, converting it to acetaldehyde (more toxic than ethanol) and then to acetate through two enzyme-mediated reactions. Blood alcohol concentration (BAC) depends on body weight, sex, food intake, and genetics, making some individuals metabolically unable to process alcohol efficiently, as seen in alcohol flush syndrome. Once intoxicated, alcohol disrupts the balance of GABA and glutamate neurotransmitters in the brain, impairing judgment and coordination. Understanding alcohol metabolism reveals why hangovers occur, why some populations have lower tolerance, and why no trick can accelerate the clearance of alcohol from the body.

Your gut is home to roughly 38 trillion bacteria, contains more neurons than your spinal cord, and sends more signals to your brain than it receives back. Here is the full mechanism — from the first bite to the last cell.

Learn how DNA replication works, which enzymes drive it, and why the error rate of 1 in a billion matters for your health.

How catalysts enable reactions without being consumed, revolutionizing chemistry