Biology 11th Edition by Cecie Starr ,Ralph Taggart

تمرين 9

Free radicals are unbound molecular fragments that have the wrong number of electrons. They form during many enzyme-catalyzed reactions, including the digestion of fats and amino acids. They slip out of electron transfer chains. They also form when x-rays and other kinds of ionizing radiation bombard water and other molecules. Free radicals are highly reactive. When they dock with a molecule, they alter its structure and function.
Superoxide dismutase is an enzyme that works with catalase to keep free radicals and hydrogen peroxide from accumulating in cells. As we age, cells make copies of enzymes in ever diminishing numbers, in altered form, or both. When this happens to superoxide dismutase and catalase, free radicals and hydrogen peroxide build up. Like loose cannonballs, they careen through cells and blast away at the structural integrity of proteins, DNA, lipids, and other molecules. For instance, look at the "age spots" on an older persons skin. Each spot is a mass of brownish-black pigments that have accumulated in skin cells. Do some research and identify other problems that arise when free radicals take over.