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Metabolism and Redox coenzymes (1).pptx

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Metabolism and Redox coenzymes (1).pptx

  1. 1. METABOLISM AND RADOX COENZYME LECTURE 1
  2. 2. Metabolism • Metabolism is a highly coordinated cellular activity in which many multi enzyme systems (metabolic pathways) cooperate to: 1. Obtain chemical energy by capturing solar energy or degrading energy-rich nutrients from the environment 2. Convert nutrient molecules into the cell’s own characteristic molecules, including precursors of macromolecules 3. Polymerize monomeric precursors into macromolecules: proteins, nucleic acids, and polysaccharides 4. Synthesize and degrade biomolecules required for specialized cellular functions, such as membrane lipids, intracellular messengers, and pigments. 12/4/2022 2 Khyber Medical University Institute of Paramedical Sciences
  3. 3. Metabolism • Metabolism is the sum of all the chemical transformations taking place in a cell or organism which occurs through a series of enzyme catalyzed reactions that constitute metabolic pathways. • Catabolism is the degradative phase of metabolism in which organic nutrient molecules (carbohydrates, fats, and proteins) are converted into smaller, simpler end products (such as lactic acid, CO2, and NH3). • Catabolic pathways release energy, some of which is conserved in the formation of ATP and reduced electron carriers (NADH, NADPH, and FADH2); the rest is lost as heat 12/4/2022 3 Khyber Medical University Institute of Paramedical Sciences
  4. 4. Metabolism • In anabolism or biosynthesis, small, simple precursors are built up into larger and more complex molecules, including lipids, polysaccharides, proteins, and nucleic acids. • Anabolic reactions require an input of energy, generally in the form of the phosphoryl group transfer potential of ATP and the reducing power of NADH, NADPH, and FADH2. 12/4/2022 4 Khyber Medical University Institute of Paramedical Sciences
  5. 5. 12/4/2022 5 Khyber Medical University Institute of Paramedical Sciences
  6. 6. ATP- the Universal Currency of Free Energy • Just as commerce is facilitated by the use of a common currency, the commerce of the cell metabolism is facilitated by the use of a common energy currency, adenosine triphosphate (ATP). • Part of the free energy derived from the oxidation of foodstuffs and from light is transformed into this highly accessible molecule, which acts as the free-energy donor in most energy-requiring processes such as motion, active transport, or biosynthesis. 12/4/2022 6 Khyber Medical University Institute of Paramedical Sciences
  7. 7. ATP- the Universal Currency of Free Energy • ATP is a nucleotide consisting of an adenine, a ribose, and a triphosphate unit • The active form of ATP is usually a complex of ATP with Mg2+ or Mn2+ • ATP is an energy rich molecule because its triphosphate unit contains two phosphor anhydride bonds. • A large amount of free energy(31 kj per mole) is liberated when ATP is hydrolyzed to adenosine diphosphate (ADP) and orthophosphate (Pi) or when ATP is hydrolyzed to adenosine monophosphate (AMP) and pyrophosphate (PPi). 12/4/2022 7 Khyber Medical University Institute of Paramedical Sciences
  8. 8. Hydrolysis of ATP to ADP and ADP to AMP 12/4/2022 8 Khyber Medical University Institute of Paramedical Sciences
  9. 9. Oxidation-reduction reactions • In living organisms, both energy-capturing and energy-releasing processes consist largely of redox reactions • Redox reactions occur when electrons are transferred between an electron donor (a reducing agent) and an electron acceptor (an oxidizing agent) • In some redox reactions, only electrons are transferred • For example, in the reaction 12/4/2022 9 Khyber Medical University Institute of Paramedical Sciences
  10. 10. Oxidation-reduction reactions • In many reactions, both electrons and protons are transferred • For example, the reaction catalyzed by lactate dehydrogenase begins with the transfer of a hydride ion (H:−), that is, a hydrogen nucleus and two electrons, from NADH to pyruvate • A proton (H+) is gained from the environment to form the final products lactate and NAD+. 12/4/2022 10 Khyber Medical University Institute of Paramedical Sciences
  11. 11. Redox Coenzymes • The coenzyme forms of the vitamin molecules nicotinic acid and riboflavin are universal electron carriers • NICOTINIC ACID : two coenzyme forms: NAD and NADP • May occur in oxidized forms (NAD+ and NADP+) and reduced forms (NADH and NADPH) • The structures of NAD+ and NADP+ both contain adenosine and the N-ribosyl derivative of nicotinamide (derived from the vitamin niacin), which are linked together through a pyrophosphate group • NADP+ has an additional phosphate attached to the 2′ OH group of adenosine 12/4/2022 11 Khyber Medical University Institute of Paramedical Sciences
  12. 12. Function • Both NAD+ and NADP+ carry electrons for several enzymes in a group known as the dehydrogenases- (Dehydrogenases catalyze hydride transfer reactions) • Many dehydrogenases that catalyze reactions involved in energy generation use the coenzyme NADH • The enzymes that require NADPH usually catalyze biosynthetic reactions (e.g., fatty acid synthesis) 12/4/2022 12 Khyber Medical University Institute of Paramedical Sciences
  13. 13. Redox Coenzymes • RIBOFLAVIN (vitamin B2) is a component of two coenzymes: flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) • FMN and FAD function as tightly bound prosthetic groups in a class of enzymes known as the flavoproteins • Flavoproteins are a diverse group of redox enzymes; they function as dehydrogenases, oxidases, and hydroxylases • FMN plays a key role in the link between two-electron transfer reactions in the mitochondrial matrix and the one-electron transfer reactions of the electron transport chain because it can transfer one hydrogen atom at a time • Succinate dehydrogenase is a prominent example of a flavoprotein • It catalyzes the oxidation of succinate by FAD to form fumarate and FADH2, an important reaction in the citric acid cycle. 12/4/2022 13 Khyber Medical University Institute of Paramedical Sciences
  14. 14. FAD and FMN 12/4/2022 14 Khyber Medical University Institute of Paramedical Sciences
  15. 15. Coenzyme A • In coenzyme A, a 3′-phosphate derivative of ADP is linked to pantothenic acid via a phosphate ester bond • The β-mercaptoethylamine group of coenzyme A is attached to pantothenic acid by an amide bond • Coenzyme A is a carrier of acyl groups that range in size from the acetyl group to long-chain fatty acids • Because the reactive SH group forms a thioester bond with acyl groups, coenzyme A is often abbreviated as CoASH • Note that sulfur is a better leaving group than oxygen • Consequently, the carbon–sulfur linkage of a thioester is a high-energy bond that is more easily cleaved than the carbon–oxygen bond of an ester 12/4/2022 15 Khyber Medical University Institute of Paramedical Sciences
  16. 16. Coenzyme A 12/4/2022 16 Khyber Medical University Institute of Paramedical Sciences

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