Mitochondria are intracellular structures responsible for harvesting the energy from food. They are bean-shaped organelles (a term referring to structures within a cell that perform a function) and have a series of external and internal membranes.
Mitochondria are the sites of cellular respiration. In cellular respiration, sugars from food are broken down, and the energy in their chemical bonds is temporarily stores in molecules of Adenosine Triphosphate, also known as ATP. ATP is the energy currency for cells, storing and releasing energy as needed. In this way, mitochondria function as the power plants for cells.
ATP has three phosphates attached to an Adenine molecule. The third phosphate group can be disconnected, and ATP becomes ADP, Adenosine Diphosphate. When the bond is broken between the second and third Phosphate molecule, energy is released. When a third phosphate is re-attached to ADP, it once again becomes ATP and energy is stored in the new chemical bond. In this way, ATP functions like a rechargeable battery, continually storing and releasing energy for cell processes.
Mitochondria take in cell sugars and essentially burn them for fuel. The energy from burning these sugars gets stored in molecules of ATP. One molecule of sugar can produce enough energy to create 36 ATP molecules.
Cell respiration begins with a step known as Glycolysis. In the cytoplasm, before entering the mitochondria, a molecule of sugar is split in half. This is glycolysis - "sugar-splitting". This splitting breaks one chemical bond, creates 2 ATP's, and makes from the sugar 2 molecules of 3-Carbon Pyruvates. These pyruvates are converted to Acetyl-CoA and these 3-carbon molecules enter the mitochondria to continue cellular respiration.
In the Mitochondria, the Acetyl-CoA molecules undergo a series of steps removing the Carbon molecules. This series of steps is cyclic, and is known as the Krebs Cycle. The carbons are bonded to Oxygen, and released as waste Carbon Dioxide. The energy from the broken bonds is temporarily stored in molecules known as electron carriers. These electron carriers move to the mitochondrial membranes where the third step of cellular respiration occurs.
In the mitochondrial membranes, there are a series of molecules through which electrons can pass. These are known together as the Electron Transport Chain, or the ETC. The ETC funnels electrons through the molecules, and produces ATP along the way. The electrons are grabbed at the end and form water molecules as a waste product. The ATP are then used by the body to energize catabolic reactions.
The mitochondria, therefore, are essential to producing usable energy for the body. They help break down food sugars, perform the process of Cellular Respiration, and additionally create the waste products exhaled. These bean-shaped intracellular organelles are vital to all living things.