ELECTRON TRANSPORT SYSTEM

ETS takes place inner membrane of mitochondria. It consists five complexes.

COMPLEX I : NADH formed in glycolysis and citric acid cycle are oxidised by NADH-dehydrogenase and the electrons are transferred to ubiquinone via FMN.

COMPLEX II: Ubiquinone also receives equivalents via FADH generated during the oxidation of succinate by succinate dehydrogenase.

COMPLEX III: The reduced ubiquinone called ubiquinol is then oxidised by transfer of electrons to cytochrome c, via cytochrome bc1 complex.

COMPLEX IV: Cytochrome c acts as a mobile carrier between complex III & IV.

Complex IV refers to cytochrome c oxidase complex containing a and a3 and two copper centres.

COMPLEX V: when the electrons are shunted over the carriers complex I to IV in the electron transport chain, they are coupled to ATP synthetase for the formation of ATP from ADP and iP.

 OXIDATIVE PHOSPHORYLATION AND SYNTHESIS OF ATP.

•Complex V or ATP synthetase consists of F0-F1 of oxysomes.

•F1 is a peripheral membrane protein complex and contains the catalytic site for ATP synthesis.

•F0 is an integral membrane protein complex, that forms the channel through which protons cross the inner membrane.

•When protons pass through this, the energy contained in them is used for the synthesis of one ATP molecule.

•Oxidation of one molecule of NADH gives to three molecules of ATP while oxidation of one moecule of FADH gives two moecules of ATP.

•Oxygen acts as terminal acceptor of hydrogen and drives the whole process by removing hydrogen from the system, hence the process iscalled oxidative phophorylation.

 RESPIRATORY QUOTIENT (RQ) 

 

•Respiratory quotient RQ = volume of Co2 evolved   

•                                                volume of O2.

•Carbohydrates RQ is 1, because equal volume of Co2 evolved and equal volume of O2 consumed.

•C6H12O6+6O2__ 6Co2+6H2O+energy.

•RQ = 6Co2

•         ------- = 1.

•           O2

•  Fat RQ is less than 1.

• 2(C51H98O6)+145O2----102Co2+98H2O+energy.

              Tripalmitin.

•RQ= 102Co2

•         ----------- = 0.7

•         145O2

•Protein RQ is more than 1. 

•2(COOH)2 + O2 ----- 4Co2 + 2H2O + energy.

•RQ=       4Co2

•            ------------ = 4.0.

•                O2

The RQ is infinite in case of anaerobic respiration because Co2 will be evolved but no oxygen is consumed