AN OVERVIEW OF BIOCHEMICAL PATHWAYS- SOURCE OF ALL METABOLIC FUEL

AN OVERVIEW OF BIOCHEMICAL PATHWAYS-
SOURCE OF ALL METABOLIC FUEL

1. AN OVERVIEW OF BIOCHEMICAL PATHWAYS- SOURCE OF ALL METABOLIC FUEL Dr. T anmay Sanyal (W.B.E.S) Assistant Professor Krishnagar Govt. College

2. Metabolism - the sum of all chemical processes carried out by living cells Catabolism - the chemical reactions that break larger molecules into smaller molecules. It is usually an exergonic process. Anabolism - the chemical reactions that form larger molecules from smaller molecules. It is usually an endergonic process. Autotroph - an organism that obtains its energy from sunlight or inorganic chemicals. Plants, photosynthetic protists , and photosynthetic prokaryotes are autotrophs. Heterotroph - an organism that obtains its energy by consuming and degrading organic molecules. Some eat other organisms, some parasitize, some degrade the remains of once-living organisms. Animals, Fungi, many protists and most prokaryotes are heterotrophs. Cells harvest chemical energy from foodstuffs in a series of exergonic reactions. The harvested energy can then be used to power energy demanding processes including endergonic reactions.

3. Glycolysis Glykys = Sweet, Lysis = splitting During this process one molecule of glucose (6 carbon molecule) is degraded into two molecules of pyruvate (three carbon molecule). Free energy released in this process is stored as 2 molecules of ATP, and 2 molecules of NADH. Glucose + 2NAD+ = 2Pyruvate + 2NADH + 2H+  G o = -146 kJ/mol 2ADP + 2Pi = 2ATP + 2H 2 O  G o = 2X(30.5 kJ/mol) = 61 kJ/mol    G o (overall) = -146+61 = -85 kJ/mol In standard condition glycolysis is an exergonic reaction which tends to be irreversible because of negative  G o .

4. → It is also called as Embden-Meyerhof Pathway (EMP) → it is defined as the sequence of reactions converting glucose or glycogen to pyruvate or lactate with production of ATP. → Enzymes takes place in cytosomal fraction of the cell. → major pathway in tissues lacking mitochondria like erythrocytes, cornea, lens etc. → it is essential for brain which is dependent in glucose for energy. → under anaerobic condition = glu + 2ADP + 2iP -----  2 Lactate + 2ATP

5. Fate of glucose in living systems Glucose + 6O 2 = 6CO 2 + 6H 2 O  G o = -2840 kJ/mol Glucose + 2NAD + = 2Pyruvate + 2NADH + 2H +  Go = -146 kJ/mol

6. Historical Perspective Glycolysis was the very first biochemistry or oldest biochemistry studied. It is the first metabolic pathway discovered. Louis Pasture 1854-1864: Fermentation is caused by microorganism. Pastuer’s effect: Aerobic growth requires less glucose than anaerobic condition. Buchner; 1897: Reactions of glycolysis can be carried out in cell-free yeast extract. Harden and Young 1905: 1: inorganic phosphate is required for fermentation. 2: yeast extract could be separated in small molecular weight essential coenzymes or what they called Co-zymase and bigger molecules called enzymes or zymase. 1940: with the efforts of many workers, complete pathways for glycolysis was established.

7. There are 10 enzyme-catalyzed reactions in glycolysis. There are two stages Stage 1: (Reactions 1-5) A preparatory stage in which glucose is phosphorylated, converted to fructose which is again forphorylated and cleaved into two molecules of glyceraldehyde-3-phosphate. In this phase there is an investment of two molecules of ATP. Stage 2: (Reactions 6-10) (Pay off phase): The two molecules of glyceraldehyde-3- phosphate are converted to pyruvate with concomitant generation of four ATP molecules and two molecules of NADH. Thus there is a net gain of two ATP molecules per molecule of Glucose in glycolysis. Importance of phosphorylated intermediates: Possession of negative charge which inhibit their diffusion through membrane. Conservation of free energy in high energy phosphate bond. Facilitation of catalysis.

8. 1. Hexokinase reaction: Phosphorylation of hexoses (mainly glucose) This enzyme is present in most cells. In liver Glucokinase is the main hexokinase ( both ISOENZYMES ) which prefers glucose as substrate. It requires Mg-ATP complex as substrate. Un-complexed ATP is a potent competitive inhibitor of this enzyme. Enzyme catalyses the reaction by proximity effect; bringing the two substrate in close proximity.

9. 2. Phosphoglucose Isomerase or Phosphohexose Isomerase: Isomerization of G6P to Fructose 6 phosphate. This enzyme catalyzes the reversible isomerization of G6P (an aldohexose) to F6P (a ketohexose). This enzyme requires Mg ++ for its activity. It is specific for G6P and F6P.

10. 3. Phosphofructokinase-1 Reaction: Transfer of phosphoryl group from ATP to C-1 of F6P to produce Fructose 1,6 bisphosphate. I I I. This step is an important irreversible, regulatory step. The enzyme Phosphofructokinase-1 is one of the most complex regulatory enzymes, with various allosteric inhibitors and activators. ATP is an allosteric inhibitor, and Fructose 2,6 biphosphate is an activator of this enzyme. IV. ADP and AMP also activate PFK-1 whereas citrate is an inhibitor.

11. 4. Aldolase Reaction: Cleavage of Fructose 1,6 bisphosphate into glyceraldehyde 3 phosphate (an aldose) and dihydroxy acetone phosphate (a ketose). This enzyme catalyses the cleavage of F1,6 biphosphate by aldol condensation mechanism. As shown below, the standard free energy change is positive in the forward direction, meaning it requires energy. Since the product of this reaction are depleted very fast in the cells, this reaction is driven in forward direction by the later two reactions.

12. 5. Triose phosphate mutase reaction: Conversion of Dihydroxyacetone phosphate to glyceraldehyde 3 Phosphate. I. This a reversible reaction catalysed by acid-base catalysis in which Histidine-95 and Glutamate -165 of the enzyme are involved.

13. 6. Glyceraldehyde-3-phosphate dehydrogenase reaction (GAPDH): Conversion of GAP to Bisphosphoglycerate. I I I. This is the first reaction of energy yielding step. Oxidation of aldehyde derives the formation of a high energy acyl phosphate derivative. An inorganic phosphate is incorporated in this reaction without any expense of ATP. NAD + is the cofactor in this reaction which acts as an oxidizing agent. The free energy released in the oxidation reaction is used in the formation of acylphosphate.

14. 7. Phosphoglycerate kinase Reaction: Transfer of phosphoryl group fron 1,3 bisphosphoglycerate to ADP generating ATP. I I I . The name of this enzyme indicates its function for reverse reaction. It catalyses the formation by proximity effect. ADP-Mg bind on one domain and 1,3BPG binds on the other and a conformational change brings them together similar to hexokinase. This reaction and the 6 th step are coupled reaction generating ATP from the energy released by oxidation of 3- phosphoglyceraldehyde. IV. This step generates ATP by SUBSTRATE-LEVEL PHOSPHORYLATION.

15. 8. Phosphoglycerate Mutase Reaction: Conversion of 3- phosphoglycerate to 2-phosphoglycerate (2-PG). In active form, the phosphoglycerate mutase is phosphorylated at His-179. There is transfer of the phosphoryl group fro m enzyme to 3-PG, generating enzyme bound 2,3-biphosphoglycerate intermediate. In the last step of reaction the phosphoryl group from the C-3 of the intermediate is transferred to the enzyme and 2-PG is released . In most cells 2,3BPG is present in trace amount, but in erythrocytes it is present in significant amount. There it regulates oxygen affinity to hemoglobin .

16. 9. Enolase Reaction: Dehydration of 2-phosphoglycerate (2-PG) to phosphoenolpyruvate (PEP). Dehydration of 2-PG by this reaction increases the standard free enrgy change of hydrolysis of phosphoanhydride bond. Mechanism: Rapid extraction of proton from C-2 position by a general base on enzyme, generating a carbanion. The abstracted proton is readily exchanges with solvent. The second rate limiting step involves elimination of OH group generating PEP

17. 10. Pyruvate Kinase Reaction: Transfer of phosphoryl group from PEP to ADP generating ATP and Pyruvate. This is the second substrate level phosphorylation reaction of glycolysis. This enzyme couple the free energy of PEP hydrolysis to the synthesis of ATP This enzyme requires Mg ++ and K +

18. Energetics and products of Glycolysis:

19. 1. Gly-3-PO 4 - -- 1,3 Bisphosphoglycerate = 6 ATP 2. 1,3 Bisphosphoglycerate-3-Phosphoglycerate = 2 ATP 3. Phosphoenolpyruvate- - Enol pyruvate = 2 ATP ATP CONSUMED: 4. Glucose---- Glucose-6-PO 4 = 1 ATP 5. Fru-6-PO 4 ---- Fru-1,6 bisphosphate = 1ATP -------- --- - --- - ---- - ----- - -- ------- Net ATP synthesized 10 – 2 = 8 ATP Energetics of Glycolysis Pathway ATP FORMED:

20. Homolactic Fermentation In an anaerobic condition or in the need of sudden need of high amount of ATP, glycolysis is the main source for generation of ATP. NAD + is one of the crucial cofactor required for GAPDH reaction. In order to regenerate NAD + from the reduced form (NADH), this reaction takes place in muscle cells . Lactate dehydrogenase (LDH) reduces pyruvate to lactate using NADH and thereby oxidizing it to NAD + Other than regenerating NAD + for running GAPDH reaction, LDH reaction is a waste of energy, and its product lactic acid brings the pH lower and causes fatigue .

21. I NH IBI T O RS Iodoacetate inhibit Gly-3-PO4 dehydrogenase involved in gly-3-PO4 to 1,3-bisphosphoglycerate Arsenate inhibit synthesis of ATP in the conversion of 1,3 bisphosphoglycerate to 3- phosphoglycerate. Fluoride inhibit enolase in conversion of 2- Phosphoglycerate to phosphoglycerate Bromohydroxyacetonephosphate - Inhibitor of dihydroxy acetone phosphate (DHAP) Oxamate - Inhibitor of Lactate dehydrogenase

22. Effect of hormones in glycolysis Insulin stimulate Hexokinase & Glucokinase by converting glucose to glu-6-PO 4 Insulin stimulate Phosphofructokinase converting fru-6-PO 4 to Fru-1,6 bisphosphate Glucagon stimulate liver glu-6-PO 4 by converting glu-6-PO 4 to glucose & fru-1,6- bisphosphate. Fru-1,6- bisphosphate is converted to fru-6-PO 4

23. Regulation of Glycolysis: There are three steps in glycolysis that have enzymes which regulate the flux of glycolysis . The hexokinase (HK) The phoshofructokinase (PFK) The pyruvate kinase

24. GLUCONEOGENESIS GLYCOGENESIS GLYCOGENOLYSIS

25. Gluconeogenesis Gluconeogenesis is the process whereby precursors such as lactate, pyruvate, glycerol, and amino acids are converted to glucose. Fasting requires all the glucose to be synthesized from these non-carbohydrate precursors. Most precursors must enter the Krebs cycle at some point to be converted to oxaloacetate. Oxaloacetate is the starting material for gluconeogenesis

26. Pyruvate is converted to oxaloacetate before being changed to Phosphoenolpyruvate 1. Pyruvate carboxylase catalyses the ATP-driven formation of oxaloacetate from pyruvate and CO 2 2. PEP carboxykinase (PEPCK) concerts oxaloacetate to PEP that uses GTP as a phosphorylating agent.

27. Gluconeogenesis is not just the reverse of glycolysis Several steps are different so that control of one pathway does not inactivate the other. However many steps are the same. Three steps are different from glycolysis. 1 Pyruvate to PEP 2 Fructose 1,6- bisphosphate to Fructose-6-phosphate 3 Glucose-6-Phosphate to Glucose

28. Regulators of gluconeogenic enzyme activity Enzyme Allosteric Allosteric Enzyme Protein Inhibitors Activators Phosphorylation Synthesis PFK ATP, citrate AMP, F2-6P FBPase AMP, F2-6P PK Alanine F1-6P Inactivates Pyr. Carb. AcetylCoA PEPCK Glucogon PFK-2 Citrate AMP, F6P, Pi Inactivates FBPase-2 F6P Glycerol-3-P Activates

29. Fructose-6-phosphate PFK-2 PFK-2 F2,6Pase F2,6Pase Fructose-2,6-bisPhosphate Fructose-1,6-bisPhosphate P P PFK-1 FBPase (+) (-) cAMP-dependent protein kinase AMP (+) ATP (-) Citrate (-) AMP (-) AMP (+) F-6-P (+) citrate (-) F-6-P (-) Hormonal control of glycolysis and gluconeogenesis

30. Glycogen Storage Glycogen is a D-glucose polymer a(1 4) linkages a(1 6) linked branches every 8-14 residues

31. Glycogen Syntheisis

32. UDP-glucose Pyrophorylase

33. Glycogen Synthase

34. Glycogen Breakdown or Glycogenolysis Three steps Glycogen phosphorylase Glycogen + Pi <-> glycogen + G1P (n residues) (n-1 residues) Glycogen debranching Phosphofructomutase

35. Glycogen Phosphorylase

36. Glycogen Debranching Enzyme

37. Coordinate control of glycogen metabolism

38. Regulation of glycogen synthesis by protein phosphatase 1. Protein phosphatase 1 stimulates glycogen synthesis while inhibiting glycogen breakdown . Active enzymes are shown in green and inactive enzymes in red.

39. Regulation of protein phosphatase 1 (PP1) in muscle takes place in two steps. Phosphorylation of G M by protein kinase A dissociates the catalytic subunit from its substrates in the glycogen particle . Phosphorylation of the inhibitor subunit by protein kinase A inactivates the catalytic unit of PP1.

40. Insulin inactivates glycogen synthase kinase. Insulin triggers a cascade that leads to the phosphorylation and inactivation of glycogen synthase kinase and prevents the phosphorylation of glycogen synthase. Protein phosphatase 1 (PP1) removes the phosphates from glycogen synthase, thereby activating the enzyme and allowing glycogen synthesis. IRS, insulin-receptor substrate.

41. Glycogen Storage Disease

42. THE CITRIC ACID CYCLE It is called the Krebs cycle or the tricarboxylic and is the “hub” of the metabolic system. It accounts for the majority of carbohydrate, fatty acid and amino acid oxidation. It also accounts for a majority of the generation of these compounds and others as well. Amphibolic - acts both catabolically and anabolically 3NAD+ + FAD + GDP + Pi + acetyl-CoA 3NADH + FADH + GTP + CoA + 2CO 2

43. History By 1930 it was established that the addition of lactate, acetate succinate, malate, a-ketoglutaric acid (dicarboxylic acids) and citrate and isocitrate (tricarboxylic acids) when added to muscle mince that they stimulated oxygen consumption and release of CO 2 1935Albert Szent-Gyorgyi showed that Succinate Fumarate Malate Oxaloacetate Carl Martius and Franz Knoop showed Citrate cis-aconitate isocitrate a ketoglutarate succinate fumarate malate oxaloacetate

44. Martius and Knoop showed that pyruvate and oxaloacetate could form citrate non-enzymatically by the addition of peroxide under basic conditions. Krebs showed that succinate is formed from fumarate , malate or oxaloacetate . This is interesting since it was shown that the other way worked as well!! Pyruvate can form citrate enzymatically Pyruvate + oxaloacetate citrate + CO 2 The interconversion rates of the intermediates was fast enough to support respiration rates.

45. Overview

46. The citric acid cycle enzymes are found in the matrix of the mitochondria Substrates have to flow across the outer and inner parts of the mitochondria

47. Pyruvate to Acetyl CoA

48. Regulation of TCA Cycle

49. AMPHIBOLIC PATHWAY 1. Cells are constantly carrying out thousands of chemical reactions needed to keep the cell, and your body as a whole, alive and healthy. These chemical reactions are often linked together in chains, or pathways . All of the chemical reactions that take place inside of a cell are collectively called the cell’s metabolism . Overview of metabolism 2. Contains both catabolic and anabolic reactions. Catabolic – Energy from oxidation of acetyl CoA is stored in reduced coenzymes. Anabolic – Several intermediates are precursors in biosynthetic pathways Krebs Cycle is Amphibolic .

50. Pentose Phosphate Pathway One fate of G6P is the pentose phosphate pathway.

51. The pentose pathway is a shunt The pathway begins with the glycolytic intermediate glucose 6-P. It reconnects with glycolysis because two of the end products of the pentose pathway are glyceraldehyde 3-P and fructose 6-P; two intermediates further down in the glycolytic pathway. It is for this reason that the pentose pathway is often referred to as a shunt.

52. It’s a shunt

53. The pentose pathway can be divided into two phases. Non-oxidative interconversion of sugars

54. NADPH + H + is formed from two separate reactions. The glucose 6-phosphate DH (G6PD) reaction is the rate limiting step and is essentially irreversible. There is a medical story for this enzyme. Cells have a greater need for NADPH than ribose 5-phosphate .

55. Regulation of the Pentose Pathway Glucose 6-phosphate DH is the regulatory enzyme. NADPH is a potent competitive inhibitor of the enzyme. Usually the ratio NADPH/NADP + is high so the enzyme is inhibited. But, with increased demand for NADPH, the ratio decreases and enzyme activity is stimulated. The reactions of the non-oxidative portion of the pentose pathway are readily reversible. The concentrations of the products and reactants can shift depending on the metabolic needs of a particular cell or tissue .

56. Where do all the NADH’s and FADH2’s Go

57. What flows from the TCA cycle to ETS is the NADH. It is the oxidation of NADH drives the production of ATP. The TCA intermediates function in other pathways, the product of this oxidative pathway, NADH is the substrate for the ETS.

58. ATP accounting so far… Glycolysis : 2 ATP Kreb’s cycle : 2 ATP Life takes a lot of energy to run, need to extract more energy than 4 ATP ! What’s the point? A working muscle recycles over 10 million ATPs per second There’s got to be a better way!

59. There is a better way! Electron Transport Chain series of molecules built into inner mitochondrial membrane along cristae transport proteins & enzymes transport of electrons down ETC linked to pumping of H + to create H + gradient yields ~34 ATP from 1 glucose ! only in presence of O 2 ( aerobic respiration )

60. Mitochondria Double membrane outer membrane inner membrane highly folded cristae enzymes & transport proteins intermembrane space fluid-filled space between membranes

61. Glycolsis Krebs cycle 8 NADH 2 FADH 2 Remember the Electron Carriers? 4 NADH G l u co s e G3P Time to break open the bank!

62. Electron Transport Chain

63. Electron Transport Chain in t e rme m b r ane space inner mi t o c h ond rial membrane NAD + Q C NADH H 2 O H + e – 2H + + 2 H + H + e – FADH 2 1 O 2 NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex mi t oc h o ndrial matrix e – H H  e- + H + NADH  NAD + + H H F A D p e Building proton gradient! What powers the proton (H + ) pumps?…

64. Electrons flow downhill Electrons move in steps from carrier to carrier downhill to O 2 each carrier more electronegative controlled oxidation controlled release of energy make ATP instead of fire !

65. H + ADP + P i H + H + H + H + H + H + H + H + We did it! A TP Set up a H + gradient Allow the protons to flow through ATP synthase Synthesizes ATP ADP + P i → A TP Are we there yet? “proton-motive” force

66. Composition of the Electron Transport Chain Four large protein complexes. Complex I - NADH-Coenzyme Q reductase Complex II - Succinate-Coenzyme Q reductase Complex III - Cytochrome c reductase Complex IV - Cytochrome c oxidase Many of the components are proteins with prosthetic groups to move electrons.

67. Flow of electrons cyt c Q Complex I Complex II Complex III Complex IV - . 4 - . 2 . . 2 . 4 . 6 . 8 1 . NADH NAD + 1/2 O 2 Path of Electrons s u c c i n at e (FADH2) fumarate + 2 H + H 2 O Energy is not released at once, but in incremental amounts at each step.

68. Inner mitochondrial membrane Outer mitochondrial membrane H + H + H + H + H + H + H + H + H + H + H + H + H + H + H + ADP + P i A TP Electron T r ans port Chain ATP synthase complex

69. Oxidative phosphorylation The electron-transport chain moves electrons from NADH and FADH 2 to O 2 . In the mean time, ADP is phosphorylated to ATP. The two processes are dependent on each other. ATP cannot be synthesized unless there is energy from electron transport . Electrons do not flow to O2, unless there is need for ATP.

70. 3 ATP are generated when two electrons are transported from NADH to O2. The oxidation of FADH2 only produces 2 ATP.

71. Th y lakoid space Photophosphorylation Stroma ADP + Pi 2H + 2H + 2H + 2H + + 1 / 2 O 2 H 2 O ATP ATP synthetase 2H + 1 / 2 O 2 2e - 2H + 2e - 2H + NADP + NADPH + + H + Thylakoid me m brane 2e -

72. Amino acid oxidation and the production of urea Waste or reuse Oxidation

73. Ammonia has to be eliminated Ammonia originates in the catabolism of amino acids that are primarily produced by the degradation of proteins – dietary as well as existing within the cell: digestive enzymes proteins released by digestion of cells sloughed-off the walls of the GIT muscle proteins haemoglobin intracellular proteins (damaged, unnecessary)

74. Ammonia is toxic, especially for the CNS, because it reacts with  - keto glutarate , thus making it limiting for the TCA cycle  decrease in the ATP level Liver damage or metabolic disorders associated with elevated ammonia can lead to tremor, slurred speech, blurred vision, coma , and death Normal conc. of ammonia in blood: 30-60 µM Ammonia has to be eliminated

75. Overview of amino acid catabolism in mammals 2 CHOICES Reuse Urea cycle Fumarate Oxaloacetate

76. Nitrogen removal from amino acids Transamination Oxidative deamination Urea cycle Aminotransferase PLP

77. Step 1: Remove amino group Step 2: Take amino group to liver for nitrogen excretion Step 3: Entry into mitochondria Step 4: Prepare nitrogen to enter urea cycle Step 5: Urea cycle Nitrogen removal from amino acids

78. Excretory forms of nitrogen Excess NH 4 + is excreted as ammonia (microbes, aquatic vertebrates or larvae of amphibia), Urea (many terrestrial vertebrates) or uric acid (birds and terrestrial reptiles)

79. Step 1 . Remove amino group Transfer of the amino group of an amino acid to an -keto acid  the original AA is converted to the corresponding -keto acid and vice versa: Type of hydrolysis H2O + NH4+

80. Transamination is catalyzed by transaminases (aminotransferases) that require participation of pyridoxalphosphate : amino acid pyridoxalphosphate Schiff base +H2O Schiff base= Amine + aldehyde coupling product

81. Step 2 : Take amino group to liver for nitrogen excretion Glutamate dehydrogenase The glutamate dehydrogenase of mammalian liver has the unusual capacity to use either NAD + or NADP + as cofactor Glutamate releases its amino group as ammonia in the liver. The amino groups from many of the a-amino acids are collected in the liver in the form of the amino group of L -glutamate molecules.

82. 1. Glutamate transfe r res one amino group WITHIN cells: Aminotransferase → makes glutamate from a-ketogluta - rate Glutamate d ehydrogenase → opposite 2. Glutamine transferres two amino group BETWEEN cells → releases its amino group in the liver 3. Alanine transferres amino group from tissue (muscle) into the liver Nitrogen carriers

83. Move within cells Synth A tase = ATP In liver Move between cells

84. Glucose-alanine cycle Ala is the carrier of ammonia and of the carbon skeleton of pyruvate from muscle to liver. The ammonia is excreted and the pyruvate is used to produce glucose, which is returned to the muscle. Alanine plays a special role in transporting amino groups to liver .

85. Sources of ammonia for the urea cycle: Oxidative deamination of Glu , accumulated in the liver by the action of transaminases and glutaminase Glutaminase reaction releases NH 3 that enters the urea cycle in the liver ( in the kidney , it is excreted into the urine) Catabolism of Ser, Thr, and His (nonoxidative deamination) also releases ammonia: Serine - threonine dehydratase Serine →→ pyruvate + NH 4 + Threonine →→ a-ketobutyrate + NH 4 + Bacteria in the gut also produce ammonia.

86. Review: Nitrogen carriers  glutamate, glutamine , alanine 2 enzymes o u tside liver, 2 enzymes inside liver: Aminotransferase (PLP) → a-ketoglutarate → glutamate Glutamate dehydrogenase (no PLP) → glutamate → a-ketoglutarate ( in liver ) Glutamine synthase → glutamate → glutamine Glutaminase → glutamine → glutamate ( in liver )

87. Step 3 : entry of nitrogen to mitochondria

88. Step 4 : prepare nitrogen to enter urea cycle Regulation

89. Step 5 : Urea cycle aspartate Ornithine transcarbamoylase Argininosuccinate synthase Argininosuccinate lyase Arginase 1

90. OOA Oxaloacetate → aspartate

91. Urea cycle – review ( Sequence of reactions ) Carbamoyl phosphate formation in mitochondria is a prerequisite for the urea cycle ( Carbamoyl phosphate synth et ase ) Citrulline formation from carbamoyl phosphate and ornithine ( Ornithine transcarbamoylase ) Aspartate provides the additiona l nitrogen to form argininosuccinate in cytosol ( Argininosuccinate synthase ) Arginine and fumarate formation ( Argininosuccinate lyase ) Hydrolysis of arginine to urea and ornithine ( A rginase )

92. The overall chemical balance of the biosynthesis of urea NH 3 + CO 2 + 2ATP → carbamoyl phosphate + 2ADP + Pi Carbamoyl phosphate + ornithine → citrulline + Pi Citrulline + ATP + aspartate → argininosuccinate + AMP + PPi Argininosuccinate → arginine + fumarate Arginine → urea + ornithine Sum: 2NH 3 + CO 2 + 3ATP  urea + 2ADP + AMP + PPi + 2Pi

93. Regulation of urea cycle N-acetylglutamic acid – allosteric activator of CPS-I High concentration of Arg → stimulation of N-acetylation of glutamate by acetyl-CoA

94. Inborn errors of amino acid metabolism

95. The Cori Cycle Lactate from active muscle is converted to glucose in liver.

96. Carl and Gerty Cori Nobel Prize in Physiology and medicine 1947 “for their discovery of the course of the catalytic conversion of glycogen”

97. Lactate and alanine are glucogenic In muscle alanine is produced from pyruvate by transamination. pyruvate + glutamate  alanine + α -ketoglutarate In the liver alanine is converted back to pyruvate. In active muscle lactate builds up, passes through the blood and is converted to pyruvate in the liver. Thus, part of the metabolic burden of active muscle is shifted to the liver.

98. Why is ATP used as the most preferable source of energy? ATP is the main source of energy for most cellular processes. ... Because of the presence of unstable, high-energy bonds in ATP, it is readily hydrolyzed in reactions to release a large amount of energy . It is much more  energy  efficient to add and remove those phosphate groups  than  to add and subtract elements from a  glucose  molecule, as there is no way to effectively break it down without significantly changing its structure, which makes it harder to build back up.

99. Reference Principles of Biochemistry: Lehninger ; 6 th edition Principles of Biochemistry: Voet & Voet ; 4 th edition Biochemistry: Stryer & Berg; 9 th edition Biochemistry: Campbell; 8 th edition Biochemistry: Satyanarayan ; 5 th edition Biochemistry: Harper; 31 st edition Slideshare.com