Lec 3 biochemistry.pdf

Biochemistry 2nd class semester 1 L3:Carbohydrates Assistant professor Ahmed Naseer Kaftan M.B.Ch.B. MSc. F.I.C.M.S Chemical pathology 1 Learning objectives: At the end of the lecture student should be able to: Underst...

Biochemistry 2nd class semester 1 L3:Carbohydrates Assistant professor Ahmed Naseer Kaftan M.B.Ch.B. MSc. F.I.C.M.S Chemical pathology 1 Learning objectives: At the end of the lecture student should be able to: Understand PDH complex Describe Krebs cycle and its regulation Describe ETC pathway and uncoupling effect Demonstrate PPP pathway Describe Glycogen metaboolism Email :[email protected] Website :http://Alkafeel.edu.iq 2 Carbohydrates Metabolism Krebs cycle & ETC  Link between Glycolysis and TCA is (CONVERSION OF PYRUVATE TO ACETYL CoA) Activated by hormone – Insulin Occurs in mitochondria Occurs in fed state Because link reaction is irreversible, therefore pyruvate can form acetyl CoA but acetyl CoA can never form pyruvate. Pyruvate is mainly derived from carbohydrates and acetyl CoA mainly form fats (TGs, Fatty Acids, Cholesterol) in the body. So we can conclude that carbohydrates (in excess) can form fats but fats can never be converted to carbohydrates because link reaction is irreversible.  Fates of pyruvate Lactate Oxaloacetate Acetyl co A Ethanol  PDH complex Complete oxidation of glucose occurs in both Cytosol (glycolysis) and mitochondria (Krebs’ cycle). In the presence of O2, pyruvate (the end product of glycolysis) passes by special pyruvate Timmy William transporter into mitochondrion which proceeds as follows:Oxidativeabout decarboxylation of pyruvate to You can talk a bit You can talk a bit this person here about this person here Acetyl-COA. Acetyl CoA is then oxidized completely to CO2, H2O through Krebs’ cycle  PDH complex Oxidative decarboxylation of pyruvate to acetyl coenzyme a (= acetyl coA) BY Pyruvate dehydrogenase (PDH) complex: It needs 5 coenzymes Timmy William You can talk a bit You can talk a bit about this person here about this person here  1) Vitamin B1 = Thiamin pyrophosphate = TPP. 2) Lipoic acid 3) Coenzyme A = CoASH. 4) Flavin adenine dinucleotide = FAD. 5) Nicotinamide adenine dinucleotide = NAD+. Location: PDH is located within the mitochondrial Timmy William matrix. You can talk a bit You can talk a bit Energy production:about → NADH+H this person here(through about respiratory this person here chain) →3ATP In vitro inhibition of PDH:  KREBS’ CYCLE Citric acid cycle (CAC), tricarboxylic acid cycle (TCA) or Catabolism of acetyl CoA Definition series of reactions in which acetyl CoA is oxidized into CO2, H2O and energy. Timmy William You can talk a bit You can talk a bit about this person here about this person here  KREBS’ CYCLE Nature of Pathway: catabolic and anabolic (Amphibolic) Neither activated by Insulin nor Glucagon Organelle: Mitochondria Organ/cell: In all the cells of the body (where mitochondria is present) A Vital Pathway for cellsTimmy William Occurs only in aerobic You conditions can talk a bit You can talk a bit Occurs both in Fedabout andthis Fasting person herestate about this person here TCA is called a cycle, not a pathway because it begins and ends with oxaloacetate  ATP number Glucose oxidation 36 or 38 ATP. Pyruvate oxidation -. 15 ATP. Acetyl CoA.. 12 ATP Timmy William You can talk a bit You can talk a bit about this person here about this person here  Functions (significance) of TCA TCA cycle is amphibolic i.e. it has catabolic and anabolic functions. Energy: 12 ATP Catabolic functions: Oxidation of carbohydrate, lipids and proteins. Anabolic functions: Formation Timmy of: William Amino acids: α-Ketoglutarate Transamination You can talk a bit Glutamate. You can talk a bit Glucose: α-Ketoglutarate Gluconeogenesis. about this person here about this person here Heme synthesis: Succinyl CoA → Heme. C02 used in (carboxylation reactions)  Regulation of TCA 3 enzymes can be rate limiting, depending on various complex conditions in the body: 1. Citrate Synthase 2. Isocitrate Dehydrogenase 3. Alpha-Ketoglutarate Dehydrogenase TCA Regulation Timmy William Inhibited by ATP, You NADH can talkand a bit succinyl You CoA. can talk These a bit compounds indicate high energy state of cell. about this person here about this person here Activated by ADP and NAD, which indicate low energy  Timmy William You can talk a bit You can talk a bit about this person here about this person here  Oxidation of extra mitochondrial NADH+H+ 1. The molecules of cytosolic NADH+H+ cannot penetrate mitochondrial membrane; however, they can be used to produce energy by respiratory chain phosphorylation in the mitochondria. Timmy William 2. This can be done by using special carriers for You can talk a bit You can talk a bit hydrogen of NADH+H+ these about this person carriers here are about this either person here (Glycerophosphate shuttle) or (Aspartate - Malate shuttle).  GLYCEROPHOSPHATE SHUTTLE It is important in certain muscles and nerve cells. The final energy produced is 2 x 2 ATP → 4 ATP. Mechanism: The coenzyme of cytosolic (glycerol -3- phosphate DH) is NAD+.,The coenzyme of mitochondrial (g3p DH) is FAD. MALATE - ASPARTATE Timmy SHUTTLE William -It is important inYou tissues particularly can talk a bit liver and heart. You can talk a bit The final energyabout produced this personis 2 x 3 about here ATPthis 6 ATP →person here - Mechanism: The coenzyme of cytosolic and mitochondrial (Malate dehydrogenase) is NAD+  Respiratory chain (electron transport chain) Definition It is the final common pathway in aerobic cells by which electrons derived from various substances are transferred to oxygen to form water. Site Timmy William Mitochondria You can talk a bit You can talk a bit about this person here about this person here  NADH (reduced nicotinamide adenine dinucleotide) and FADH2 (reduced form of flavin adenine dinucleotide) are produced by glycolysis, b-oxidation of fatty acids, the TCA cycle, and other oxidative reactions. NADH and FADH2 pass electrons to the components of the ETC, which are located in the inner mitochondrial membrane.  Mitochondrial membrane Mitochondrial membranes: The mitochondrion contains an outer and an inner membrane separated by the intermembrane space.  Mitochondrial matrix The gel-like solution of the matrix (interior) of mitochondria contain enzymes responsible for the oxidation of pyruvate, amino acids, and fatty acids (by b-oxidation) as well as those of (TCA) cycle. The synthesis of glucose, urea, and heme occurs partially in the matrix of mitochondria. In addition, the matrix contains NAD+ and FAD (the oxidized forms of the two coenzymes that are required as electron acceptors), and ADP and Pi, which are used to produce ATP.  Organization of the respiratory chain - The inner mitochondrial membrane contains 5 fixed enzyme complexes, called complex I, II, III,IV and V. Complex V catalyses ATP synthesis. a) Each complex accepts or donates electrons to relatively 2 mobile electron carriers such as coenzyme Q and cytochrome C. Timmy William b) Each carrier of electron transport chain can receive electrons from the more electronegative You can talk a bit about this person here You can talk a bit about this person here donor to the next more electropositive carrier in the chain.Finally electrons combine with oxygen and protons to form water.  Stages of electron transport 1. Transfer of electrons from NADH to coenzyme Q 2. Transfer of electrons from CoQ to cytochrome c 3. Transfer of electrons from cytochrome c to oxygen Two electrons are required to reduce 1 atom of O2; therefore, for each mole of NADH that is oxidized, 1/2 mole of O2 is convertedTimmy to H2O. William The energy produced by the transfer of electrons from cytochrome c to O2about is used to pump protons about thisacross the You can talk a bit You can talk a bit this person here person here inner mitochondrial membrane.  Oxidative phosphorylation 1. Electrons are transferred down the respiratory chain from NADH to oxygen. This is because NADH is a strong electron donor, while oxygen is a strong electron acceptor. 2. The flow of electrons from NADH to oxygen Timmy William (oxidation) results in ATP synthesis by phosphorylation ofabout ADP by inorganic You can talk a bit this person here phosphate “Pi” You can talk a bit about this person here (phosphorylation). Therefore, there is a coupling between oxidation and phosphorylation.  Chemiosmotic hypothesis: (Mitchell hypothesis). 1. Proton pump: a. The transport of electrons down the respiratory chain → Gives energy. b. This energy is used to transport H+ from the mitochondrial matrix → across inner mitochondrial membrane → inter membrane space. c. This is done by complexes I, lll and IV.  d. This process creates across the inner mitochondrial membrane: i. An electrical gradient: (with more positive charges on the outside of the Membrane than on the inside) ii. A pH gradient: (the outside of the membrane is at lower pH than the inside). e. The energy generated by this proton gradient is sufficient for ATP synthesis.  2. ATP synthase (complex V): a) It is formed of 2 subunits: b) The protons outside the inner mitochondrial membrane can re-enter the mitochondrial matrix by passing through ATP synthase enzyme. This results in the synthesis of ATP from ADP + Pi. At the same time decrease the pH and electrical gradients.  Leakage of electrons from the ETC produces reactive oxygen species (ROS), such as superoxide. hydrogen peroxide. and hydroxyl radicals. ROS damages DNA and Timmy proteins and causesWilliamlipid peroxidation. Enzymes You cansuch as superoxide talk a bit You can talk a bit dismutsae (SOD}.about catalase, and glutathione this person here about this person here peroxidase are cellular defenses against ROS  Inhibitors of respiratory chain ▪ Are compounds preventing the passage of electrons by binding to a component of the chain, blocking the oxidation, reduction reaction.  Uncouplers of respiratory chain These are substances that allow oxidation to proceed but prevent phosphorylation. So energy released by electron transport will be lost in the form of heat. This explains the cause of hotness after intake of these Timmy William You can talk a bit You can talk a bit about this person here about this person here Pentose phosphate pathway  Pentose Phosphate Pathway (Hexose Phosphate Pathway): Definition: It is an alternative pathway for glucose oxidation where: 1. ATP (energy) is neither produced nor utilized. 2. Its main function is to produce NADPH Timmy William,H and pentoses. You can talk a bit You can talk a bit Location about this person here about this person here 1. Intracellular location: Cytosol  Organ location: a) It is active in tissues where NADPH+H+ is needed for fatty acids synthesis. 1- Adipose tissue and liver. 2- Adrenal cortex and gonads. 3- Red cells 4- Retina Timmy William b) In many tissues:You Itcansupplies talk a bit pentoses You canfor talk a bit synthesis of nucleotides. about this person here about this person here  REACTIONS (STEPS) Two phases: oxidative and non-oxidative: 1. Oxidative (irreversible) phase: Where 3 molecules of “glucose-6-phosphate” are converted into 3 molecules of “Ribulsose-5-phosphate” with production of NADPH+H+ and CO2. 2. Non-oxidative (reversible) Timmy phase: William Where the 3 molecules of “ribulose-5-phosphate” You can talk a bit You can talk a bit are interacted and converted into here about this person 2 molecules ofperson here about this “glucose-6-phosphate” and one molecule of “glyc-3- phosphate”. REACTIONS (STEPS) Timmy William You can talk a bit You can talk a bit about this person here about this person here REACTIONS (STEPS) Timmy William You can talk a bit You can talk a bit about this person here about this person here NADPH Uses  Glucose 6-phosphate dehydrogenase G6PD catalyzes the oxidation of glucose 6-phosphate to 6-phosphogluconolactone , rate-limiting, and regulated step of the pathway. The nonoxidative reactions of the pentose phosphate pathway occur in all cell types synthesizing nucleotides and nucleic acids.  G6PD deficiency (favism) is a hereditary condition characterized by hemolytic anemia caused by the inability to detoxify oxidizing agents. G6PD deficiency is the most common disease-producing enzyme abnormality in humans. Glycogen metabolism  Glycogen metabolism Glycogen is the major storage form of carbohydrate in animals, consists of chains of a-1,4– linked D-glucose residues with branches that are attached by a-1,6 linkages The main stores of glycogen are found in skeletal muscle and liver,  Location of glycogen: Glycogen is present mainly in cytosol of liver and muscles. A. Liver glycogen is about 120 grams (about 6 % of liver weight). B. Muscle glycogen is about 350 grams (about 1 % of total muscle weight).  Functions of glycogen: A. Liver glycogen: It maintains normal blood glucose concentration especially during the early stage of fast (between meals). After 12-18 hours fasting, liver glycogen is depleted. B. Muscle glycogen: It acts as a source of energy within the muscle itself especially during muscle contractions.  Glycogenesis 1. Activation of Glucose to (UDPGlucose): 2. Formation of glycogen primer: which: Few molecules of glucose react with OH of tyrosine of a protein called glycogenin. 3. Glycogen synthase; “Key enz.” UDP-G molecules are added to glycogen primer causing elongation of the α1-4 branches up to 12-14 glucose units. 4. Branching enzyme: Transfers parts of the elongated chains (5-8 glucose residues) to the next chain forming a new α1-6 glycosidic bond.  Glycogenolysis 1. Phosphorylase “Key enz.”. -Acts on α1-4 bonds, breaking it down by phosphorolysis. – It removes glucose units in the form of glucose- 1-phosphate. It acts on the branches containing more than 4 glucosyl units. 2. Transferase: When the branch contains 4 glucose units, 3 of them are transferred to a next branch by transferase enzyme leaving the last one. 3.Debranching enzyme: Removes the last glucose unit that is attached to the original branch by α1-6 bond. Regulation of glycogen metabolism Timmy William You can talk a bit You can talk a bit about this person here about this person here  Fate of glucose-6-phosphate: a) In liver: glucose-6-phosphate is converted to glucose by glucose-6-phosphatase. b) In muscles: there is no glucose-6-phosphatase, so glucose-6 phosphate enters glycolysis to give lactate. Timmy William You can talk a bit You can talk a bit about this person here about this person here  Glycogen storage diseases: Definition: These are group of inherited disorders characterized by deposition of abnormal type or quantity of glycogen in the tissues.  Discussion ‫تخصيص وقت للنقاش التفاعلي مع الطلبة‬ 14/9/202 Email :[email protected] Website :http://Alkafeel.edu.iq 60 3 References Lippincott’s Illustrated Reviews: Biochemistry Textbook of Medical Biochemistry. M.D. Chatterjea, M. N Email :[email protected] Website :http://Alkafeel.edu.iq 61