English to French Medical Medical (general)

Under no circumstances does hemoglobin make contact with oxygen molecule; because if it did, it would oxidize and thus, not allow any oxygen to reach other cells. But under normal circumstances it does not have to come into contact with oxygen as it has been created in a very special manner so as not to face this danger. Instead, it holds the oxygen molecule as if "with a pair of tongs". How does hemoglobin capture oxygen? Hemoglobin protein is composed of four subunits, each containing an iron atom bound to a heme group. These heme groups are the special "tongs" that give hemoglobin the ability to capture oxygen without contact and carry it to the cells that need it.

Je ne capte pas trop la comparaison avec les tongs, quelqu'un peut-il m'expliquer? Merci