How Does the Cell Harvest Energy Released During the Catabolism of Food Molecules?

Cellular respiration is one of the most important processes that takes place in your body--in fact, you couldn't stay alive an instant without it. Through cellular respiration, your cells extract the energy they need from molecules in your food.

Features

• Cellular respiration involves three separate series of reactions, namely, glycolysis, the citric acid cycle and oxidative phosphorylation. Glycolysis breaks down glucose into pyruvate, which feeds into the citric acid cycle, which powers oxidative phosphorylation in turn. All three of these processes use the energy released by breaking down glucose to synthesize a molecule called adenosine triphosphate or ATP.

Function

• ATP is the energy currency of the cell. When ATP loses a phosphate group to become adenosine diphosphate or ADP, the reaction that occurs releases energy. By using energy from glucose catabolism to synthesize ATP, your cells can store the energy in a form they can use in other parts of the cell. In muscle cells, for example, a protein called myosin binds to ATP; when the ATP molecule breaks to form ADP, the shape of the myosin protein changes so that it tugs on a filament. The concerted action of multiple myosin proteins pulling on filaments causes the muscle fiber to contract.

Significance

• Reactions that cause an increase in total entropy--either the entropy of their surroundings or the entropy of the system in which the reaction takes place--are spontaneous, while reactions that cause entropy to decrease are not. Your body uses reactions that increase total entropy, like the breakdown of glucose sugar molecules, to release energy to drive other reactions and processes that are entropically unfavorable.