BIOENERGETICS
FREE ENERGY It is the portion of the total energy change in a system that is available for doing work at constant temperature and pressure; it is represented as ΔG. Reactions involving free energy: 1. Exergonic 2. Endergonic
EXERGONIC REACTIONS Reactions in which the free energy of the final state is less than the free energy of the initial state. This represents energy that can be used to do biological work Reaction is spontaneous or favorable. ΔG is - or <0
ENDERGONIC REACTIONS Reactions in which the free energy of the initial state is less than the free energy of the final state. ΔG is + or >0 Reaction is nonspontaneous or unfavorable Considerable amount of energy must be imparted to the system
COUPLED REACTIONS: 2 TYPES 1. Coupling involves a common obligatory intermediate (I) A+C I B+D 2. Synthesizing a compound of high-energy potential in the exergonic reaction and incorporate this new compound into endergonic reaction. AH 2 Carrier BH 2 A Carrier-H 2 B The overall free energy change for the reaction is negative (ΔG < 0)
HIGH ENERGY PHOSPHATES High energy phosphates play central role in energy capture & transfer. E X E R G O N I C 2 3 1 4 E SYNTHESIS MUSCULAR CONTRACTION NERVOUS EXCITATION ACTIVE TRANSPORT
HIGH ENERGY COMPOUNDS Compound ΔG (Kcal/mol) Phosphoenolpyruvate -14.8 1,3 bisphosphoglycerate -11.8 Phosphocreatine -10.3 ATP( ADP+Pi) -7.3 AMP(Adenosine+Pi) -3.4 PPi( 2Pi) -4.0 Glucose-1-phosphate -5.0 Fructose-6-phosphate -3.8 Glucose-6-phosphate -3.3
ENERGY CURRENCY OF CELL High energy phosphates act as energy currency of cell. 3 major sources of high energy phosphates taking part in energy conservation or energy capture. 1. Oxidative phosphorylation: Free energy to drive this process comes from Respiratory chain oxidation using molecular O 2 in mitochondria.
2. Glycolysis: 3. TCA Cycle:
ROLE OF ATP/ADP CYCLE IN TRANSFER OF HIGH ENERGY PHOSPHATES SUCCINYL Co-A PEP 1,3 BPG P ATP OXIDATIVE PHOSPHORYLATION CREATINE- P store of P CREATINE P ADP G6P Glycerol3P Other Phosphorylations Gl 1,6 BP
BIOLOGICAL OXIDATION
BIOMEDICAL IMPORTANCE Respiration Xenobiotics (metabolism by Cytochrome P450 system). Hyperbaric oxygen therapy in patients with respiratory or circular failure. May result oxygen toxicity.
ENZYMES INVOLVED IN OXIDATION & REDUCTION: OXIDOREDUCTASES Oxidases Dehydrogenases Hydroperoxidases Oxygenases
OXIDASES Catalyse the removal of hydrogen from a subtrate using oxygen as a hydrogen acceptor. AH 2 1/2 O 2 e.g. 1. Cyt. Oxidase AH 2 A A H 2 O O 2 H 2 O 2 2. L-AA oxidase 3. Xanthine oxidase 4. Glucose oxidase
DEHYDROGENASES Transfer of hydrogen from one substrate to another in a coupled oxidation - reduction reaction. Can t use O 2 as H 2 acceptor. AH 2 A Carrier -H 2 Carrier BH 2 B Depend on: 1. Nicotinamide coenzymes 2. Flavin coenzymes 3. Cytochromes
HYDROPEROXIDASES Use H 2 O 2 or organic peroxides as substrates. 2 types: 1. Peroxidases 2. Catalases
H 2 O 2 + AH 2 Peroxidases 2H 2 O + A 2GSH + Glutathione peroxidase H 2 O 2 2H O+ 2 GSSG 2H 2 O 2 Catalases 2H 2 O + O 2
OXYGENASES Catalyze direct incorporation of oxygen into a substrate. Takes place in 2 steps: 1. O 2 binding to the enzyme at active site, & 2. The reaction in which bound O 2 is reduced/transferred to substrate. 2 subgroup of oxygenases: i. Dioxygenases ii. Monooxygenases
Dioxygenases: Incorporate both atoms of molecular oxygen into the substrate. e.g. A+O 2 AO 2 i. Homogentisate oxidase ii. L-tryptophan dioxygenase iii. 3-hydroxyanthranilate dioxygenase
Monooxygenases: Incorporate only one atom of molecular oxygen into the substrate. May be Microsomal or Mitochondrial. A-H + O 2 + ZH 2 A-OH + H 2 O + Z DRUG-H + O 2 + 2Fe 2+ + 2H + DRUG-OH + H 2 O + 2Fe 3+ Hydroxylase
RESPIRATORY CHAIN & OXIDATIVE PHOSPHORYLATION
Respiratory chain oxidizes reducing equivalents and acts as a proton pump. Oxidative phosphorylation is the process by which liberated free energy is trapped as high-energy phosphate.
ELECTRON TRANSPORT CHAIN 4 sequential complexes found in the inner side of inner mitochondrial membrane. They accept e - from e - donors such as NADH or succinate, shuttle these e - across the membrane creating an electrical & chemical gradient (+1.1V). Through the proton driven chemistry of the ATP synthase, generate ATP.
COMPLEXES OF ETC Complex II- Succinate - Coenzyme Q reductase Complex I - NADH dehydrogenase/ NADH Coenzyme Q reductase. Fp Q ½ O 2 + H + Complex III - Coenzyme Q - cytochrome c oxidoreductase H 2 O Cyt-C Complex IV - Cytochrome c oxidase.
ETC COMPONENTS Complex Components Prosthetic group I II III IV NADH-Q oxidoreductase Succinate Q reductase Q-Cytochrome C oxidoreductase Cytochrome c oxidase ATP synthase FMN Fe-S FAD Fe-S Heme b H Heme b L Heme C1 Fe-s Heme a Heme a3 CuA & CuB
Oxidative phosphorylation- Two phases H+ H+ H+ H+ H+ H+ 1. Generation of the proton gradient. H+ H+ H+ H+ H+ H+ H+ ATP H+ H+ H+ H+ H+ H+ 2. Using the gradient's energy to make ATP
TRANSPORT OF REDUCING EQUIVALENTS THROUGH ETC AH 2 NAD + FpH 2 2Fe 3+ H 2 O A NADH Fp 2Fe 2+ ½ O 2 H + H + 2H + 2H +
Pyruvate Lipoate α - Ketoglutarate Proline 3- Hydroxyacyl - CoA 3- Hydroxybutyrate Glutamate Malate Isocitrate Fp [FAD] NAD Glycerol 3 phosphate I Fp [FMN] FeS Fp [FAD] FeS Acyl - CoA Sarcosine Dimethylglycine Succinate Choline Fp [FAD] FeS Q FeS ETF [FAD] Fp [FAD] II
III IV Q Cyt b FeS Cyt c 1 Cyt c Cyt aa 3 Cu O 2
Q CYCLE CYTOSOL (OUTSIDE) INNER MITOCHONDRIAL MEMBRANE MATRIX (INSIDE) H + QH 2 H + e - e - b 566 QH QH H + e - C 1 Q b 562 H +
ATP Synthase a subunit binds to outside of ring Exterior column has 1 a subunit 2 b subunits, & the δ subunit Moving unit (rotor) is c ring & γε Remainder is stationary (stator) F 1 subunit has 5 types of polypeptide chains (α 3, β 3, γ, δ, ε) F 0 contains the proton channel ring of 10-14 c subunits
Subunit a Proton enters Proton exits
The Binding Change Mechanism (Paul Boyer)
P:O RATIO When substrates oxidized by NADdehydrogenase, 3 mol ATP is produced per ½ mol of O 2 consumed. P:O= 3. When substrates oxidized by AFDdehydrogenase, 2 mol ATP is produced per ½ mol of O 2 consumed. P:O= 2.
INHIBITORS OF ETC
N A D H Complex II Malonate Succinate Complex I Oligomycin FAD FeS Carboxin TTFA Complex III Complex IV FMN,FeS Q Cyt b, FeS, Cyt c Cyt a Cyt a 1 Cyt c 3 Cu Cu Piericidine Amobarbital Rotenone BAL Antimycin A Uncouplers CN, CO Azide, H2S O H 2 O ADP + Pi ATP ADP + Pi ATP ADP + Pi ATP
CHEMIOSMOTIC THEORY (Mitchell) OLIGOMYCIN H + Inner Mitochondrial membrane ATP synthase NADH +H + I H + ADP+Pi H + ATP NAD + Proton translocation Q III H + Uncouplers H + + H + _ 1/2O 2 H 2 O C IV H +
Transport of Reducing Equivalents SHUTTLE PATHWAYS
SHUTTLE PATHWAYS Two pathways: 1. Glycerol Phosphate Shuttle - Muscle & Brain 2. Malate-Aspartate Shuttle - Liver, kidney & heart They transport the reducing equivalents from cytosol to mitochondria and not vice versa.
Malate aspartate shuttle Cytosol Liver, kidney & heart Mitochondria NAD + NADH + H + Malate Malate dehydrogenase Oxaloacetate α -KG 1 α -KG Malate Malate dehydrogenase Oxaloacetate NAD + NADH + H + Transaminase Transaminase Glutamate Asp Asp Glutamate 2 H + H +
Glycerophosphate shuttle Cytosol Mitochondria Muscle & brain NAD + Glycerol 3 phosphate Glycerol 3 phosphate FAD NADH + H + Glycerol 3 PO 4 dehydrogenase Dihydroxy acetone phosphate Glycerol 3 PO 4 dehydrogenase Dihydroxy acetone phosphate FADH 2 Resp. chain
TRANSPORTER SYSTEMS N-Ethylmaleimide H 2 PO 4 H + Malate -2 Citrate -3 +H + α-kg -2 OUTSIDE ATP 4- Atractiloside 1 2 3 4 5 6 INSIDE OH - Pyruvate HPO 4-2 Malate -2 Malate -2 ADP 3-1. Phosphate 2. Pyruvate 3. Dicarboxylate 4. Tricarboxylate 5. α-kg 6. Adenine nucleotide