The OXPHOS System Yesterday (IMAGE)
Caption
The figure shows the classical textbook representation of the oxidative phosphorylation system. Briefly, five big molecular machines named complex I to complex V performed the process of conversion of the energy extracted from the breakage of the food (in the form of electrons of high energy: NADH+H+ or FADH2) into energy useful for be spent in the different processes needed for the cell survival, maintenance, growth and division (in the form of ATP). The proportion of NADH+H+/FADH2 high-energy electrons generated in the cells depends of the source of food, being higher with sugar and lower with fat. The process is made in two steps. In the first, complexes I, II, III and IV generate a single branched circuit to extract the energy of the high-energy electrons. These complexes move freely in the mitochondrial inner membrane but do not physically interact. Therefore to allow the electrons to flux between complexes I or II to complex III, a small molecule called coenzyme Q (CoQ) receive the electrons and is transformed (reduced CoQH2). Then diffuse through the membrane until it reach complex III and deliver the electrons becoming again oxidized coenzyme Q (CoQ) ready to pick up again electrons from either complex I of complex II. A similar role is performed by a small protein call cytochrome c (cyt c) to transfer electrons between complexes III and IV. In complex IV the electrons interact with Oxygen and participate in the formation of water. This flux of electrons between complexes I or II and complex IV releases enough energy in complexes I, III and IV but not complex II, to pump protons across the membrane were they are located (mitochondrial inner membrane). The protons are accumulated at one side of the membrane that is impermeable to them. As much accumulation is produce much greater is the natural tendency to equilibrate its amount at both sides of the membrane. Complex V uses this tendency as the driving force to generate ATP the energy currency within the cell.
Credit
CNIC
Usage Restrictions
None
License
Licensed content