Electron Transport Chain and oxidative phosphorylation

substrate level phosphorylation and chemiosmosis
in Eukaryotes and in prokaryotes
in plant and animal
uncoupler oxidative phosphorylation
fat and protein ATP calculation

1. Electron Transport Chain An  electron transport chain (ETC) is a cluster of proteins that transfer electrons through a membrane to creates an electrochemical  proton gradient  that drives the synthesis of  (ATP) ATP is used by the  cell  as the energy for metabolic processes for cellular function It couples electron transfer with the transfer of  protons  (H +  ions) across a  membrane

2. Synthesis of ATP Substrate level phosphorylation(ADP+P=ATP) Chemiosmosis(in 1961 British biochemist peter Mitchel proposed for chemosmotic model and awarded noble prize in 1978. )

3. APPLICATION   photosynthesis  or,  cellular respiration . In  eukaryotes , an oxidative phosphorylation  through the action of  ATP synthase . In chloroplasts , in the  thylakoid  membrane of the  chloroplast light drives the  conversion  of  water  to  oxygen  and  NADP +  to NADPH electrons  are moving due to the energy input of light e- transport chains  in chloroplasts use the  lipid-soluble  e- carriers  plastoquinone In  mitochondria , in the  inner mitochondrial membrane it is the conversion of oxygen to water , NADH to NAD +   electrons  were lent to the ETC by the NADH.   e- transport chain   in  mitochondria  uses the  lipid-soluble  e- carrier  ubiquinone In  prokaryotes  ( bacteria  and  archaea ) the situation is more complicated, In   bacteria , the electron transport chain is located in their  cell membrane reverse electron transport  is important in many prokaryotic electron transport chains.   Autotrophs   can use this process to supply reducing power for inorganic  carbon fixation

4. • Complex I (NADH Dehydrogenase) Has 42 different polypeptide chains. Transfers 2 electrons from NADH to Q. Pumps 4 protons from matrix to IMS. • NADH > FMN > Fe-S cluster > ubiquinone (flavin mononucleotide) (coenzyme Q) inhibited by Alkylguanides Rotenone ,  Barbiturates ,  Chlorpromazine ,  • Complex II (succinate dehydrogenase) • Entry point for FADH2. Transfers 2 electrons from succinate to coenzyme Q. Contains 4 different protein subunits: inhibited by  Carboxin . . • Complex III (cytochromes b, and c) Composed of 22 subunits: heme groups Transfers of 2 electrons ubiquinol to Cytochrome C. Pumps 4 protons into IMS. inhibited by  dimercaprol   Napthoquinone and Antimycin. 11 protrin subunit • Complex IV • Combination of cytochromes a and a3, 13 protein subunits, 2 types of prosthetic groups: 2 cytochromes and 2 Cu. Transfers 2 electrons from cytochrome C to oxygen, reducing it to H2O. Pumps 2 protons into IMS inhibited by  cyanide ,  carbon mo n oxide ,  azide , and   hydrogen sulphide (H 2 S). COMPONENTS OF ETC

5. NADH+H + → Complex I → Q → Complex III → cytochrome c → ComplexIV → H 2 O ↑ Complex II ↑ Succinate COMPONENTS OF ETC • NAD & Flavoprotein : H-carriers in celluiar respiration • Non heme metalloprotein (Fe-S- Protein): Iron cycles between 3+ and 2+ states. • Ubiquinone or CoQ : region serves as an anchor to inner mitochondrial membrane. • Cytochromes : Electron-transfer proteins that contain a heme prosthetic group

6. Oxidative phosphorylation The coupling of redox reactions of the respiratory chain with the phosphorylation of ADP constitutes a reaction complex known as oxidative phosphorylation It  takes place in the inner mitochondrial membrane , in contrast with most of the reactions of the citric acid cycle and fatty acid  oxidation , which take place in the matrix . Uncouplers of oxidative phosphorylation  in mitochondria inhibit the coupling between the electron transport and  phosphorylation  reactions and thus inhibit ATP synthesis without affecting the respiratory chain and ATP synthase  brown adipose tissue —provides for an alternative flow of protons back to the inner mitochondrial matrix. Thyroxine is also a natural uncoupler. This alternative flow results in  thermogenesis  rather than ATP production. Synthetic uncouplers (e.g.,  2,4- DNP,  2,4-dinitrocresol , ) also exist, and can be lethal at high doses.

7. Protein & FAT metabolism under aerobic conditions Glucogenic amino acids can contribute in gluconeogenesis (glucose synthesis) during prolonged exercise. ketogenic amino acids, cannot be used to synthesize glucose, rather they synthesize triacylglycerol. 8 carbon fatty acid give 4 acetyl co acetate (12*4=48ATP)