Adenosine triphosphate consists of three groups of phosphate attached to an adenine (purine) and a ribose (sugar). Adenine is an organic base that creates uric acid upon oxidation. Oxidation is the contact with oxygen. ATP creates energy when it is transferred into the cell. During the process, the chemical bond is severed releasing energy and creating adenosine diphosphate -- ADP. ADP then attaches itself to another phosphate, creating ATP, and the process begins again.
The function of the cell determines the size, shape and location of the mitochondria. For instance, A muscle cell mitochondrion would be different than a heart cell mitochondrion, which would in turn be different than a liver cell mitochondrion. Depending on how metabolically active the cell is determines the amount of mitochondria in each cell, ranging from hundreds to thousands. Each mitochondrion possess two membranes. The outer membrane completely surrounds the organelle, and the inner membrane consists of foldings, which allows for an increase in surface area. The amount of mitochondria is increased only through the division of other existing mitochondria.
Other than its function, mitochondria have certain unique qualities. Mitochondria possess their own DNA that is independent of the DNA housed in the nucleus of the cell. It is this separate DNA that becomes flawed as we grow older, resulting in age-related debilitating muscular problems and weakness. As organisms evolved, certain bacteria changed its structure and developed into organelles that eventually became mitochondria.
The food we eat allow the mitochondria to produce energy for our cells to utilize. This energy is used for three distinct functions: the synthesis of new chemical compositions, the transportation of molecules through cell membranes so they may fulfill their functions and the application of mechanical work, such as the pumping of the heart muscle or the contraction of skeletal muscles.