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Oxidation and reduction

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Oxidation and reduction

  1. 1. oxidation and reduction pbl G5 case 4
  2. 2. objectives 1. define the oxidation and reduction and compare between them 2. explain the mechanism of catabolism of food and know the difference in alcohol metabolism case. 3. define both of NAD and FAD and ATP the chemical structure for each one 4. explain how NAD and FAD involved in metabolism of food 5. explain the synthesis of FADH2 and NADH
  3. 3. Oxidation-Reduction The key chemical event in an oxidation-reduction reaction is the net movement of electrons from one reactant to another reactant. The movement occurs from the reactant with less attraction of electrons to the reactant with more attraction for electrons. Some Redox Terminology Oxidation: is loss of electrons Reduction is gain of electrons
  4. 4. Example
  5. 5. Oxidation Number An oxidation state is a number that is assigned to an element in a chemical combination. This number represents the number of electrons that an atom can gain, lose, or share when chemically bonding with an atom of another element.
  6. 6. Reducing and Oxidizing Agents
  7. 7. NAD NADH, short for nicotinamide adenine dinucleotide, is an important pyridine nucleotide that functions as an oxidative cofactor in eukaryotic cells. NADH plays a key role in the production of energy through redox reactions. NAD serves as a cofactor for dehydrogenases, reductases and hydroxylases, making it a major carrier of H+ and e- in major metabolic pathways such as glycolysis, the tricarboxylic acid cycle, fatty acid synthesis and sterol synthesis
  8. 8. NAD structure C21H27N7O14P 2 663.43 g/mol
  9. 9. CONVERSION OF NAD TO NADH This is an oxidation reaction where 2 hydrogen atoms (or 2 hydrogen ions and 2 electrons) are removed from the organic metabolite. (The organic metabolites are usually from the citric acid cycle (krebs cycle) and the oxidation of fatty acids). One hydrogen is removed with 2 electrons as a hydride ion (H−H−) while the other is removed as the positive ion (H+H+). Usually the metabolite is some type of alcohol which is oxidized to a ketone.
  10. 10. FAD Flavin adenine dinucleotide (FAD) is a condensation product of riboflavin and adenosine diphosphate. It is the coenzyme of various aerobic dehydrogenases, e.g., D-amino acid oxidase and L-amino acid oxidase. In biochemistry, flavin adenine dinucleotide (FAD) is a cofactor in redox reactions. There are two main portions of FAD: (1) adenine and (2) Flavin mononucleotide. The two portions are joined together at their phosphate groups. FAD occurs in different redox states: quinone, semiquinone, and hydroquinone. It converts between one state to another either by accepting or donating electrons. FAD can be produced by the reduction and dehydration of flavin-N(5)-oxide.
  11. 11. Structure of FAD Molecular Formula: C27H33N9O15P2 Molecular Weight: 785.557 g/mol
  12. 12. FAD conversion into FADH2 The conversion of FAD to FADH2 is an example of a reduction reaction. In this case flavin adenine dinucleotide (FAD) gains 2 electrons and 2 hydrogen atoms. The reaction is: FAD+2e−+2H+↔FADH2 FAD can be seen as a carrier for electrons. This reduction reaction happens in the citric acid cycle when fumarate is formed from succinate.
  13. 13. •Flavoproteins are enzymes that catalyze redox reactions using either flavin mononucleotide (FMN) or flavin adenine dinucleotide (FAD) as coenzymes. •These coenzymes are derived from the vitamin riboflavin. •Although the flavin coenzymes are water soluble, they are bound tightly to the enzyme. Tightly bound coenzymes are called prosthetic groups. As a result the flavin coenzymes do not transfer electrons from one enzyme to another, but allow the flavoprotein to temporarily hold the electrons to catalyze an electron transfer from a substrate to the electron acceptor.
  14. 14. •The fused ring shown in red is an isoalloxazine ring which undergoes reversible reduction. The isoalloxazine ring can accept either one electron or two. The fully reduced flavins are abbreviated FADH2 or FMNH2. •FAD the oxidized or quinone form. FADHx the radical or semiquinone form. FADH2 the reduced or hydroquinone form
  15. 15. •FAD the oxidized or quinone form. • FADHx the radical or semiquinone form. •FADH2 the reduced or hydroquinone form
  16. 16. •FAD accepts and donates 2 electrons with 2 protons (2 H):FAD + 2 e - + 2 H + FADH2
  17. 17. ADENOSINE TRIPHOSPHATE (ATP) All living things, plants and animals, require a continual supply of energy in order to function. The energy is used for all the processes which keep the organism alive. Some of these processes occur continually, such as the metabolism of foods, the synthesis of large, biologically important molecules, e.g. proteins and DNA, and the transport of molecules and ions throughout the organism. Other processes occur only at certain times, such as muscle contraction and other cellular movements.However, before the energy can be used, it is first transformed into a form which the organism can handle easily. This special carrier of energy is the molecule adenosine triphosphate, or ATP.
  18. 18. STRUCTURE OF ATP The ATP molecule is composed of three components. At the centre is a sugar molecule, ribose (the same sugar that forms the basis of RNA). Attached to one side of this is a base (a group consisting of linked rings of carbon and nitrogen atoms); in this case the base is adenine. The other side of the sugar is attached to a string of phosphate groups. These phosphates are the key to the activity of ATP.
  19. 19. HOW IT WORKS The bonds between the phosphate groups of ATP’s tail can be broken by hydrolysis Energy is released from ATP when the terminal phosphate bond is broken This reaction releases a lot of energy, which the organism can then use to build proteins, contact muscles, etc. The reaction product is adenosine diphosphate (ADP), and the phosphate group either ends up as orthophosphate (HPO4) or attached to another molecule. This release of energy comes from the chemical change to a state of lower free energy, not from the phosphate bonds themselves When the organism is resting,the reverse reaction takes place and the phosphate group is reattached to the molecule. Thus the ATP molecule acts as a chemical 'battery', storing energy when it is not needed, but able to release it instantly when the organism requires it.
  20. 20. Glycolysis *The first stage of respiration. *Glycolysis takes place in the cytoplasm of cells. *During this process one molecule of glucose (6 carbon molecule) is degraded into two molecules of pyruvate (three carbon molecule).
  21. 21. krebs cycle Following glycolysis, the mechanism of cellular respiration involves another multi-step process—the Krebs cycle, which is also called the citric acid cycle or the tricarboxylic acid cycle. The Krebs cycle uses the two molecules of pyruvic acid formed in glycolysis and yields high-energy molecules of NADH and flavin adenine dinucleotide (FADH2), as well as some ATP. Steps In order for pyruvate from glycolysis to enter the Kreb's Cycle it must first be converted into acetyl-CoA by the pyruvate dehydrogenase complex which is an oxidative process wherein NADH and CO2 are formed. Another source of acetyl-CoA is beta oxidation of fatty acids. 1. Acetyl-CoA enters teh Kreb Cycle when it is joined to oxaloacetate by citrate synthase to produce citrate. This process requires the input of water. Oxaloacetate is the final metabolite of the Kreb Cycle and it joins again to start the cycle over again, hence the name Kreb's Cycle. This is known as the committed step 2. Citrate is then converted into isocitrate by the enzyme aconitase. This is accomplished by the removal and addition of water to yield an isomer. 3. Isocitrate is converted into alpha-ketogluterate by isocitrate dehydrogenase. The byproducts of which are NADH and CO2. 4. Apha-ketogluterate is then converted into succynl-CoA by alpha-ketogluterate dehydrogenase. NADH and CO2 are once again produced. 5. Succynl-CoA is then converted into succinate by succynl-CoA synthetase which yields one ATP per succynl-CoA.
  22. 22. 1. Succinate coverts into fumarate by way of the enzyme succinate dehydrogenase and [FAD] is reduced to [FADH2] which is prosthetic group of succinate dehydrogenase. Succinate dehydrogenase is a direct part of the ETC. It is also known as electron carrier II. 2. Fumarate is then converted to malate by hydration with the use of fumarase. 3. Malate is converted into oxaloacetate by malate dehydrogenase the byproducts of which are NADH.
  23. 23. Electron Transport Chain The energy released in these e- transfers is used to pump H+ (protons) out of the matrix into the intermembrane space. This produces a proton gradient (different [H+] on each side) – a state of high potential energy. 1a. At enzyme complex I, NADH is oxidized to NAD+ and e- are transferred between different proteins in this cluster, then to coenzyme Q (CoQ or Ubiquinone). Protons are pumped. 1b. FADH2 is oxidized (transfers its e-) to the CoQ at enzyme complex II. The reduced CoQ joins the rest of the “chain”. 2. The reduced CoQ travels to enzyme complex III where the e- are transferred between proteins and then to cytochrome c. Protons are pumped.
  24. 24. 3. Cytochrome c travels to the enzyme complex IV where the e- are transferred between proteins and then to O2 to form water. More protons are pumped. The H+ ions that have been pumped into the intermembrane space can only get back into the matrix through ATP Synthase. The energy released as H+ flow back to the matrix is coupled with the formation of ATP: ADP+Pi →ATP+H2O (oxidative phosphorylation 1) Each NADH that enters the electron transport chain produces 3 ATP molecules (i.e H+ ions are pumped at complexes I, III and IV) whereas each FADH2 (that joins the “chain” at complex two) produces 2 ATP molecules (i.e H+ ions are pumped only at complexes III and IV)
  25. 25. Synthesis of ATP A cell has two ways of generating ATP: Chemiosmosis Substrate level phosphorylation Chemiosmosis is the production of ATP due to hydrogen ion gradient across a membrane. According to chemiosmotic model, the electron transport chain in the inner mitochondria has proton pumps. In 1961, Peter Mitchell realised that the buildup of hydrogen ions on one side of a membrane would be a source of potential energy and that the movement of ions across the membrane, down an electrochemical gradient, could provide the energy needed to power the formation of ATP from ADP and Pi. He called this chemiosmosis theory.
  26. 26. Structure of Mitochondria Mitochondria have an inner and outer phospholipid membrane. The outer membrane is smooth and the inner membrane is folded into cristae Between the inner and outer membranes is the intermembrane space. The matrix is enclosed by the inner membrane, its where the link reaction and Krebs cycle takes place The inner membrane is impermeable to most small ions, including hydrogen ions (protons) and has embedded in it many electron carriers and ATP synthase enzymes. Some of the electron carriers have a coenzyme that pumps (using energy released from the passage of electrons) protons from the matrix to the intermembrane space.
  27. 27. Because the inner membrane is impermeable to small ions, protons accumulate in the intermembrane space, building up a proton gradient – a source of potential energy.
  28. 28. Chemiosmosis The ATP synthase enzymes are large and protrude from the inner membrane into the matrix and allow protons to pass through them. Protons flow down a proton gradient, through the ATP synthase enzymes, from the intermembrane space into the matrix. This flow is called chemiosmosis. The force of this flow drives the rotation of part of the enzyme and allows ADP and Pi (inorganic phosphate) to be joined to make ATP. Oxidative phosphorylation is the formation of ATP by the addition of inorganic phosphate to ADP in the presence of oxygen. Hence production of ATP by chemiosmosis is Oxidative phosphorylation. 4H+ + 4 e– + O2 → 2H2 O
  29. 29. Question An average adult human with a typical weight of 70 Kg consumes about 65 Kg of ATP per day. How could you explain this? Answer : The average adult human consumes approximately 11,700kJ (2800 Calories) per day. About 50% of metabolic pathways leads to production of ATP ,thus of the 11,700 kJ a person consumes , about 5850 kJ ends up as ATP. The hydrolysis of 1 mole of ATP produces 50 kJ of energy . This means the body cycles through 5850/50 =117 moles of ATP each day . The disodium salt of ATP has a molecular weight of 551 g/mol .
  30. 30. So , an average person hydrolyzes about : 117 moles 551 g/mole = 64,467 g of ATP per day✖ 64,467 / 1000 = 64 Kg The average adult human ,with a typical weight of 70 kg consumes approximately 64 kg per day, an amount nearly equal to the person’s weight .
  31. 31. Anaerobic respiration Anaerobic respiration is the metabolic process in which oxygen is absent, and only the stage of glycolysis is completed. This process occurs mostly in microorganisms, but it can also be a temporary response to anoxic, or oxygen-less, conditions in the cells of multicellular organisms . In the absence of oxygen . pyruvate can follow one of two metabolic pathways: lactate (lactic acid) fermentation. alcoholic fermentation :occurs in plants and yeasts which are respiring anaerobically
  32. 32. lactate fermentation. ● The pyruvate from glycolysis is converted in a single step to lactate (lactic acid). ● The reaction is catalysed by lactate dehydrogenase and the process requires hydrogen from NADH
  33. 33. alcoholic fermentation ● Pyruvate is first converted to ethanal by decarboxylation (removal of carbon dioxide). ● The carbon dioxide is released as a gas. ● Acetaldehyde (Ethanal)is then reduced to ethanol using hydrogen from NADH.
  34. 34. references books: ❖ Advanced biology , Michael Kent , Oxford , chapter 6:Respiration , 6-2 glycolysis and fermentation , page 102 and 103 . ❖ Introduction-to-organic-and-biochemistry-7th-edition Guyton and Hall Textbook of Medical Physiology 12th Edition
  35. 35. references wibesites: ❖ https://highered.mheducation.com/sites/dl/free/0073525502/930160/mad25502_ch08.pdf ❖ http://www.pearsonschoolsandfecolleges.co.uk/AssetsLibrary/SECTORS/Secondary/PDFs/Science/HeinemannScience/OCRALevelSampleLessons/OCRA2Biology_StudentBook97804356 ❖ https://www.slideshare.net/scuffruff/glycolysis https://www.youtube.com/watch?v=FE2jfTXAJHg ❖ https://www.khanacademy.org/science/biology/cellularfermentation/glycolysis/a/glycolysis ❖ https://www.google.com.sa/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&uact=8&ved=0ahUKEwjg-p3a2pnTAhXGUBQKHVw5A_wQFghaMAc&url=http%3A%2F%2Fwe ❖ https://www.google.com.sa/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&uact=8&ved=0ahUKEwjg-p3a2pnTAhXGUBQKHVw5A_wQFghRMAY&url=https%3A%2F%2Fw ❖ https://www.google.com.sa/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&cad=rja&uact=8&ved=0ahUKEwjg-p3a2pnTAhXGUBQKHVw5A_wQFghIMAU&url=https%3A%2F%2Fso ❖ https://pubchem.ncbi.nlm.nih.gov/compound/flavin_adenine_dinucleotide#section=Top ❖ http://www.biology-nline.org/dictionary/Flavin_adenine_dinucleotide ❖ http://www.laney.edu/wp/cheli-fossum/files/2012/01/Electron-transport-chain.pdf ❖ http://www.chm.bris.ac.uk/motm/atp/atp1.htm ❖ http://www.nslc.wustl.edu/courses/Bio2960/labs/Metabolism%20Lecture.pdf ❖ https://books.google.co.uk/books?id=iGPsen3fSOIC&pg=PA66&lpg=PA66&dq=amount+of+at ❖ Http://Www.Chem.Uwec.Edu/Webpapers2001/Clareymm/Pages/Intro/Nadintro.Html ❖ https://www.boundless.com/biology/textbooks/boundless-biology-textbook/cellular-respiration-7/energy-in-living-systems-73/electrons-and-energy-353-11579/ ❖ https://chem.libretexts.org/Core/Biological_Chemistry/Vitamins,_Cofactors_and_Coenzymes/Nicotinamide_Adenine_Dinucleotide_(NAD) ❖ https://chem.libretexts.org/Core/Biological_Chemistry/Vitamins,_Cofactors_and_Coenzymes/Nicotinamide_Adenine_Dinucleotide_(NAD)
  36. 36. thank you pbl G5

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  • Mariam Abou Touk - 110291
    NADH produced during glycolysis must be oxidised back to NAD+ to be used again in glycolysis. If this did not happen, NAD+would soon run out and the production of ATP would halt.
    If oxygen is available, NAD+ is regenerated when NADH releases hydrogen into the mitochondria. The hydrogen enters the electron transport system and generates about six more molecules of ATP . However. if oxygen is unavailable, NAD+ is regenerated by fermentation, a process in which no more ATP molecules are generated.
  • Mariam Abou Touk - 110291
    Glycolysis transfers only a small proportion of the energy in glucose to ATP. Anaerobic organisms have to satisfy their energy needs by glycolysis.
    despite its low level of ATP production. However, aerobic organisms can use oxygen to release a much greater proportion of the energy in glucose to make many more ATP molecules via the Krebs cycle, the next stage of aerobic respiration, and ultimately via the electron transport system.
  • Mariam Abou Touk - 110291
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