Presentation on theme: "The Importance of Energy Changes and Electron Transfer in Metabolism The potential energy of the water at the top of a waterfall is transformed into kinetic."— Presentation transcript:
The Importance of Energy Changes and Electron Transfer in Metabolism The potential energy of the water at the top of a waterfall is transformed into kinetic energy in spectacular fashion.
p.416 The synthesis of glucose and other sugars in plants, the production of ATP from ADP, and the elaboration of proteins and other biological molecules are all processes in which the Gibbs free energy of the system must increase. They occur only through coupling to other processes in which the Gibbs free energy decreases by an even larger amount. There is a local decrease in entropy at the expense of higher entropy of the universe.
Ilya Prigogine (1977) won Nobel Prize
Oxidation-reduction reactions: redox reactions; electrons are transferred from donor to acceptor. Oxidation : loss of electrons; reduction: the gain of electrons Substance that losses e - : the one that is oxidized (reducing agent/reductant) Substance that gains e - : the one that is reduced (oxidizing agent/oxidant) How are oxidation and reduction involved in metabolism? alkane alcoholaldehyde Carboxylic acid CO 2 eg. Oxidation process
p.420 The half reaction of oxidation of ethanol to acetaldehyde Many biologically important redox reactions involve coenzymes, such as NADH and FADH 2. These coenzymes appear in many reactions as one of the half-reactions that can be written for a redox reaction.
p.421 Another important electron acceptor is the oxidized form of FADH 2. Other several coenzymes contain flavin group; derived from the vitamin riboflavin (vit B 2 )
ATP can be hydrolized easily and the reaction releases energy The coupling of energy- producing reactions and energy-requiring reactions is a central feature in metabolism of all organisms The phosphorylation of ADP to produce ATP requires energy (can be supplied by oxidation of nutrients) The hydrolysis from ATP to ADP releases energy FIGURE 15.5 The phosphoric anhydride bonds in ATP are highenergy bonds, referring to the fact that they require or release convenient amounts of energy, depending on the direction of the reaction.
High energy bond: term for a reaction in which hydrolysis for a specific bond releases a useful amount of energy. Another way to indicate such a bond is ~P. The energy of hydrolysis of ATP is not stored energy, just an electric current – ATP and electric current must be produced when they are needed. FIGURE 15.7 Hydrolysis of ATP to ADP (and/or hydrolysis of ADP to AMP) High energy bond
Table 15-1, p.425
Fig. 15-8, p.425
Fig. 15-9, p.426 The oxidation processes takes place when the organism needs the energy that can be generated by the hydrolysis of ATP Example: Lets examine biological reaction that release energy. Glucose 2 Lactate ions G°= kJmol -1 = kcal mol -1 2 ADP + 2 P i 2 ATP G°= 61.0 kJ m mol -1 = 14.6 kcal mol -1 The overall reaction: Glucose + 2 ADP + 2 P i 2 Lactate ions + 2 ATP The hydrolysis of ATP produced by breakdown of glucose can be coupled by endergonic processes. eg. muscle contraction in exercise (jogger/long distance-swimmer)
Activation process is where a step frequently encountered in metabolism. A component of metabolic pathway (metabolite) is bonded to other molecule, coenzyme, and the free enrgy change for breaking this new bond is negative. eg. A – metabolite, B – substance A + coenzyme A-coenzyme A-coenzyme + B AB + coenzyme Example of coenzyme: coenzyme A (CoA) Fig , p.428
Fig , p.429
Fig , p.430
In carbohydrate metabolism, glucose-6-phosphate reacts NADP + to give 6-phosphoglucono-δ-lactone. In this reaction, which substance is oxidized and which is reduced? Which substance is oxidizing agent and which is reducing agent?
there is a reaction in which succinate reacts with FAD to give fumarate and FADH 2. In this reaction, which substance is oxidized and which is reduced? Which substance is oxidizing agent and which is reducing agent?
Electron transport and oxidative phosphorylation
Oxidative phosphorylation: the synthesis of ATP from ADP using energy from mitochondrial electron transfer from NADH + H + and FADH 2 to O 2. (ADP + P i ATP) Give rise to most of the ATP production associated with the complete oxidation of glucose. Substrate-level phosphorylation: the synthesis of ATP from ADP using energy from the direct metabolism of a high energy reactant. (A-P + ADP B + ATP). This reaction occur in glycolysis and Kreb cycle (carbohydrate metabolism).
Fig. 20-1, p.541
Fig. 20-2, p.541 C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + 36 ATP Note: on average, 2.5 moles of ATP are generated for each mole of NADH and 1.5 moles of ATP are produced for each mole of FADH 2.
Essential information The e - transport chain consists of four multi-subunit membrane-bound complexes and two mobile e - carriers (CoQ and cytochrome c) The reaction that take place in three of these complexes generate enough energy to drive the phosphorylation of ADP to ATP. Complex I known as NAD-CoQ oxidoreductase – catalyzes the first steps of e - transport chain. (NADH to CoQ) this complex includes several proteins that contain an iron-sulfur cluster and the flavoprotein that oxidizes NADH. proven to be a challenging task because of its complexity (iron-sulfur clusters). CoQ is mobile - it is free to move in the membrane and pass the e - to complex III for further transport to O 2
Fig. 20-5, p.546 NADH + H + + CoQ NAD + + CoQH 2
Complex II catalyzes the transfer of e - to CoQ, known as succinate- CoQ oxidoreductase. its source of e - is differs from oxidizable substrate (NADH) – the substrate is succinate (from TCA/Kreb cycle), which is oxidized to fumarate by a flavin enzyme. Succinate + E-FAD Fumarate + E-FADH 2 E-FADH 2 + Fe-S oxidized E-FAD + Fe-S reduced Fe-S reduced + CoQ + 2H+ Fe-S oxidized + CoQH 2 the overall reaction is exergonic, but theres not enough energy to drive ATP production + no hydrogen ions pumped out of the matrix during this step.
Complex III CoQH 2 -cytochrome c oxidoreductase (cyt reductase) catalyzes the oxidation of reduced coenzyme Q (CoQH 2 ) – the e - are passed along to cyt c. CoQH Cyt c [Fe (III)] CoQ + 2 Cyt c [Fe (II)] + 2 H + note: the oxidation of CoQ involves two e -, whereas the reduction of Fe (III) to Fe (II) requires only one e - two molecules of cyt c are required for every molecule of CoQ
Complex IV The 4 th complex, cytochrome c oxidase, catalyzes the final steps of e - transport transfer the e - from cyt c to oxygen. cytochrome c oxidase is an integral part of the inner mitochondrial membrane and contains cyt a and a3 and two Cu 2+ (is an intermediate e - acceptors that lie between two a-type cyt). The overall reaction: 2 Cyt c [Fe(II)] + 2 H + + ½ O 2 2 Cyt c [Fe(III)] + H 2 O Cyt c Cyt a Cu 2+ Cyt a 3 O 2 Both cyt a form the complex known as cytochrome oxidase. The reduced cytochrome oxidase is then oxidized by O 2, which reduced to water.
So, from all four complexes, there are 3 places where e - transport is coupled to ATP production by proton pumping: NADH dehydrogenase reaction Oxidation of cyt b Reaction of cytochrome oxidase with O 2
Cytochromes and other Iron-Containing Proteins of Electron Transport Fig. 20-9, p.551 NADH, FMN and CoQ, the cytochromes are macromolecules and found in all types of organisms and located in membrane.
Fig , p.555
In glycolysis (carbohydrate metabolism), the NADH produced in cytosol, but NADH in the cytosol cannot cross the inner mitochondrial membrane to enter the e - transport chain. The e - can be transferred to a carrier that can cross the membrane. The number of ATP generated depends on the nature of the carrier.
Fig , p.561 Glycerol-phosphate shuttle - This mechanism observed in mammalian muscles and brain.
Fig , p.562 Malate-aspartate shuttle - Has been found in mammalian kidney, liver and heart.
Table 20-3, p.563
4 different sources of energy available for working muscles after rest: Creatine phosphate- reacts directly in substrate-level phosphorylation to produce ATP Glucose from glycogen muscles stores; initially consumed by anaerobic metabolism Glucose from the liver (glycogen stores and gluconeogenesis) – consumed by anaerobic metabolism Aerobic metabolism in the muscles mitochondria.