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Web Bit 3-2: Molecules with Similar Shapes Can Mimic One Another By Allan Tobin The general arrangement of atoms in a molecule determines many of its properties, including, for example, whether it is polar or nonpolar. But the specific arrangement of atoms determines the molecule's size and shape. In many cases, the shape and charge distribution of a molecule---much more than its chemical properties---determines its biological effects. Synthetic molecules made in the laboratory, for example, may have shapes and charge distributions so similar to those of natural compounds that the synthetic versions mimic biological effects. A particularly dramatic example of such mimicry is the drug amphetamine, whose three-dimensional structure closely resembles epinephrine, a powerful chemical signal Epinephrine, secreted by the adrenal glands, helps coordinate the "fight or flight" reaction, by which animals respond to threats. It is a stimulant that increases heart rate and blood pressure, redistributes blood to the muscles, and raises blood sugar. Figure 3.2: Amphetamine and epinephrine. During World War II, flyers and soldiers on all sides used amphetamine to keep alert during night missions. Amphetamine may also cause a host of side effects, including restlessness, euphoria, headaches, dry mouth, constipation, and weight loss. After 1945, returning soldiers continued to use the drug and amphetamine became a widely abused drug in both Japan and the United States. Today amphetamine is still widely prescribed by physicians as a treatment for obesity, hyperactivity in children, and narcolepsy, the overwhelming tendency to fall asleep. Because the brain cannot regulate the effects of amphetamine as it regulates those of epinephrine, amphetamine has severe disorganizing effects on the brain. Fatigue and depression inevitably follow the use of amphetamines. Chronic amphetamine intoxication tends to result in insomnia, irritability, hyperactivity, and personality changes. Overdose produces tremors, confusion, assaultive behavior, hallucinations, and panic, as well as nausea, vomiting, and abdominal cramps. Fatal overdose is preceded by convulsions and coma. |