Mitochondria are found in eukaryotes and are the site of respiration that releases large amounts of energy in the form of ATP. Firstly, the structure of mitochondria is described. Mitochondria are double membrane cells that were once independent prokaryotic cells, but later became the parts of the eukaryotes. They also possess their own circular DNA and 70S ribosomes. The outer membrane is smooth and has transport protein embedded into them. The inner membrane is folded into cristae and is a site of Electron Transport Chain, and has ATP synthase. The space between outer and inner membranes is called an intermembrane space that has a low pH due to the high amount of H+ ions. The aqueous solution within the membrane is called the matrix that contains DNA, ribosomes,, and enzymes that play an important role in the later stages of aerobic respiration.
The structural adaptations of mitochondria help them in performing their function efficiently. The transport proteins in the outer membrane allow the entry of pyruvate that forms in glycolysis (the initial step of respiration). The pyruvate then enters the matrix where it takes part in the link reaction and Krebs cycle. The outer membrane is more permeable than the inner membrane.
The inner membrane has numerous folding which increases the surface area that holds enzymes and ETC hence increases the rate of reactions. When there will be more surface area, there will be more electron transport chain carriers and ATP synthase enzymes that will result in an increased production of ATP. It is also the site of oxidative phosphorylation using ATP synthase enzyme and diffusion of protons. The electron carriers release electrons and energy, pumping protons to move from matrix to the intermembrane space. As the inner membrane is less permeable, it does not allow protons to pass back; hence there is a high concentration. Instead, the proton motive force causes H+ ions to move into the matrix via ATP synthase, generating an electrochemical gradient that produces ATP via chemiosmosis.
The matrix has various enzymes and compounds that play an integral part in link reaction and Krebs cycle. Also, it has many ribosomes, tRNA and proteins, that all function at a suitable pH.
