Biophysical principle of energy conversion in mitochondria

Biophysical principle of energy conversion in mitochondria
Mitochondria are often referred to as the powerhouses of the cells. The energy made by the mitochondria is a chemical called adenosine triphosphate or ATP. ATP is the form of energy that our cells need for their essential functions and that is what keeps us alive. The process in which the mitochondria forms the ATP is called the electron transport chain. It consists on oxidizing the major products of glucose(a sugar present in all the food we eat): pyruvate, and NADH, which are produced in the cytosol. This process of cellular respiration, also known as aerobic respiration, is dependent on the presence of oxygen.



Description of the process
This chain is made up of 4 complexes which are groups of proteins that work together to carry out their function, the 5th complex is responsible for the final step of the energy generation. They are placed in the thinner mitochondrial membrane and parts of the first, third, fourth and fifth complexes are coded for by the mitochondrial DNA. In order for energy to be generated several steps have to occur.

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Electrons are passed between the complexes of the electron transport chain and enable the cells to generate energy. The first complex accepts the electrons that are produced from the degradation of the food we eat. As it passes the electrons to the third complex in the chain, protons are moved across the inner mitochondrial membrane (H+ ions). At complex three the electrons from complex one are joined by others donated by complex two. Complex three passes these electrons onto complex four and in the process moves more protons across the inner mitochondrial membrane. Within complex four the electrons are joined to oxygen to produce water, alongside one final movement of protons. Since so many protons have now been moved across the membrane into the intermembranous space, the amount of H+ is higher on the outside of the membrane than on the inner, this creates a gradient. Complex five then uses this gradient to produce ATP through the movement of H+ into the matrix. The proton gradient rotates this final complex and with each rotation an ATP is made. For every cycle of the electron transport chain over 30 ATPs are produced, this shows how efficient energy generation is within the mitochondria.

Importance in clinical medicine

 * In 1963, researchers discovered that mitochondria have their own DNA different from the one found in the others cells’ nucleus. There are more than 40 different identified diseases that have different genetic feature but all of them make the mitochondria unable to completely burn food and oxygen in order to generate energy. Therefore, the incompletely burned food might accumulate as poison inside the body decreasing the reliability of other reactions along the body.


 * In newborn infants, a large amount of Brown Adipose Tissue is located on the upper half of the spine and towards the shoulders; its main function is to regulate the internal heat - protect the baby from hypothermia (serious problem of premature newborns and a major cause of death) because BAT mitochondria generate energy in the form of heat rather than ATP.


 * There are several drugs and toxins that inhibit oxidative phosphorylation. Although any one of these toxins inhibits only one enzyme (complex target) in the electron transport chain, inhibition of any step in this process will halt the rest of the process. Here is a diagram with a description of some of them

Conclusion
Mitochondrias are a unique property of some cells capable of producing ATP required for living. The process of ATP formation occurs in the mitochondria and it is thus a target for medical research due to some metabolic disorders and also drugs.