Medical brain notes 25

  Introduction   The oxidative degradation of carbohydrates, fats and amino acids at cellular level needs oxygen and any metabolism after complete oxidation forms CO 2  and H 2 O. Hence, any biological oxidation taking place at tissue level is associated with the uptake of oxygen and release of carbon dioxide and rapidly liberates energy. This biological oxidation accompanied by specific enzymes and coenzymes in a step wise fashion involves the union between hydrogen atoms with oxygen atom to form water. During the electron transport, the electrons are transferred from organic substrates to oxygen yielding energy in the generation bond energy in the form of Adenosine triphosphates (ATP) from Adenosine diphosphates (ADP). ATP and ADP are known as high energy phosphates as the cleavage of phosphate bond in them yield energy and inorganic phosphate. This energy is utilized for the anabolic and catabolic processes. The oxidative phosphorylation enables the aerobic living orga...

  Redox Couple   Always every  oxidation is accompanied by a reduction process . All such reactions are termed as  oxidation-reduction reactions  and shortly referred as  redox . These  redox  reactions are associated with movements of electron. The electron donor is called as reductant or reducing agent and the electron acceptor, the oxidant or oxidizing agent. The system which transfer its electron is changed into oxidant form while the system which accepts electrons gets converted to the reductant form. Oxidation reduction system is simplified and shown below (fig 8.1) A specific example is oxidation of ferrous iron to ferric iron indicates the removal of electron (e-)from ferrous iron. Since, the electron is not stable in the free form it gets attached to another molecule and thus every oxidation is followed by a reduction. Always these redox reactions are energy yielding. A direct transfer of electrons from substrate to the oxidant would libe...

  Electron transport chain The electron transport chain (figure 8.2) consists of series of proteins which tightly bound involves the passage of a pair of electrons from one chemical to the next, whereby each chemical in the sequence has less reduced energy than the previous. The electron transport chain oxidizes (i.e. “burns”) the NADH+H+ and FADH 2  cofactors, using molecular oxygen as the final electron acceptor. In the electron transport chain electron carriers and hydrogen-electron acceptors are positioned alternatively to carry the function. There are three different regions in the electron transport chain, where energy is released. In each region there is a formation of one ATP. All these reactions and capturing of energy takes place in mitochondria.   1.  Components of mitochondria with marker enzymes   The histochemical and ultra centrifugation studies clearly established that the major site of cellular oxidation is mitochondria. These are sub cellular o...

  Oxidative phosphorylation   Hydrogens or their electrons, pass down the electron transport chain in a series of redox reaction. The electrons entering the electron transport system have relatively high energy content. As they pass along the chain of electron acceptors, they lose much of their energy, some of which is used to pump the protons across the inner mitochondrial membrane. The flow of electrons in the electron transport is usually coupled tightly to the production of ATP with the help of the enzyme ATP synthetase, and it does not occur unless the phosphorylation of ADP can also proceed. This prevents a waste of energy, because high-energy electrons do not flow unless ATP can be produced. Because the phosphorylation of ADP to form ATP is coupled with the oxidation of electron transport components, this process of making ATP is referred to as oxidative phosphorylation. The electron transport and oxidative phosphorylation depends upon the availability of ADP and Pi and...

  High energy compounds   The high energy compound is the ATP. The other high energy compoundsinclude ADP,1,3-diphospho glycerate, phosphoenol pyruvate and also creatine phosphate.   The phosphate group of the high energy phosphate may transfer directly to another organic compound. For this reason the term group transfer potential is preferred by some high energy bond. However, the phosphorylated compound may or may not have high energy phosphate bond, though the total energy content of the molecule is higher than a non phosphorylated compound.   Storage form of high energy compounds   They are called as  phosphogens  and help to store the high energy. The example for this the creatine phosphate present in the vertebrate muscles, the reaction works in both directions it is a reversible reaction form ATP when ATP is required. When ATP is more, creatine reacts with ATP and forms the phosphocreatine.   1. 1, 3-diphosphoglycerate One of the phosphate ...