Mitochondria Research Paper

Essay 79: Mitochondria

Mitochondria are organelles found exclusively in eukaryotic cells, meaning protozoa, fungi, plants, and animals. The term 'mitochondrion' is derived from a Greek word meaning thread. This accurately describes their appearance in the light microscope, as barely visible thread like structures. Following the invention of the electron microscope, scientists learned that mitochondria have a complex structure that allows them to harness metabolic energy in a useful form. As an aside, prokaryotic cells (eubacteria, blue-green algae, and archebacteria) lack mitochondria but maintain a strong evolutionary kinship with them. Biologists believe that free living, aerobic prokaryotes gave rise to mitochondria over 1 billion

Because the entire structure of the mitochondria is optimized for the production of a proton gradient, a more accurate description of these organelles would be "the cell's batteries". Specifically, mitochondria are the site of aerobic respiration, where sugars and fatty acids are broken down in the presence of oxygen to produce energy in the form of ATP. Carbon dioxide is formed as a byproduct. As we shall see, far more ATP is generated by the mitochondria than by the cytosolic enzymes responsible for anaerobic glycolysis. Glycolysis, or anaerobic respiration, is the first phase of sugar breakdown at the cellular level. Simple sugars such as glucose, fructose, and galactose are converted to a three carbon compound called pyruvate. Because this process occurs in the cytosol and does not require oxygen, it is termed anaerobic. The net energy yield from anaerobic respiration is two molecules of ATP. In the absence of oxygen, pyruvate is converted to lactic acid, which is a metabolic dead end. Although the liver can convert lactic acid to pyruvate and pyruvate back into glucose, this requires the hydrolysis of more

Some contain an enzyme called CYP450 SCC (side chain cleavage), which converts cholesterol to pregnenolone. This specialized function is restricted to mitochondria in the adrenal cortex, testes, and ovaries. Subsequent steps of steroid hormone synthesis are catalyzed by enzymes located in the smooth endoplasmic reticulum (sER).

Heat production Finally, mitochondria in specialized adipose tissue called brown fat generate heat by short circuiting the electron transport chain. As in other cells, these mitochondria burn fatty acids aerobically. The major difference is these mitochondria contain a specialized protein called thermogenin, which allows protons to flow from the intermembrane space back into the mitochondrial matrix without having to pass through the ATP synthetase complex. As such, these mitochondria produce heat at the expense of ATP production. This process is not wasteful, however; the heat generated by brown fat ensures that arterial blood remains liquid even at low temperatures. By extension, lipolysis of brown fat helps maintain core body