CHAPTER 08

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It is very,informative,but i think the presentation could be little elaborative.

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Chapter 8:

From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Chapter 8 Section 8.1: Glycolysis Section 8.2: Gluconeogenesis Section 8.3: The Pentose Phosphate Pathway Section 8.4: Metabolism of Other Important Sugars Section 8.5: Glycogen Metabolism Carbohydrate Metabolism Overview

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Chapter 8: Overview From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Energy transforming pathways of carbohydrate metabolism include: glycolysis , glycogenesis , glycogenolysis , gluconeogenesis , and pentose phosphate pathway Figure 8.1 Major Pathways in Carbohydrate Metabolism

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Section 8.1: Glycolysis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Glycolysis (anaerobic process) occurs in almost every living cell Ancient process central to all life Splits glucose into two three-carbon pyruvate units Catabolic process that captures some energy as 2 ATP and 2 NADH Figure 8.1 Major Pathways in Carbohydrate Metabolism

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Section 8.1: Glycolysis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Glycolysis is an anaerobic process Two stages (stage 1 and 2): energy investment and energy producing Figure 8.2 Glycolytic Pathway

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Section 8.1: Glycolysis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Glycolytic Pathway: D -Glucose + 2 ADP + 2 P i + 2 NAD +  2 pyruvate + 2 ATP + 2 NADH + 2 H + + 2 H 2 O Figure 8.2 Glycolytic Pathway

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Section 8.1: Glycolysis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Reactions of the Glycolytic Pathway 1. Synthesis of glucose-6-phosphate Phosphorylation of glucose ( kinase ) prevents transport out of the cell and increases reactivity 2. Conversion of glucose-6-phosphate to fructose-6-phosphate Conversion of aldose to ketose Figure 8.3 Glycolytic Pathway Hexokinase Phosphoglucoisomerase

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Section 8.1: Glycolysis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Reactions of the Glycolytic Pathway Continued 3. Phosphorylation of fructose-6-phosphate This step is irreversible due to a large decrease in free energy and commits the molecule to glycolysis 4. Cleavage of fructose-1,6-bisphosphate Aldol cleavage giving an aldose and ketose product Figure 8.3 Glycolytic Pathway PFK-1 Aldolase Triose Phosphate Isomerase

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Section 8.1: Glycolysis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Reactions of the Glycolytic Pathway Continued 5. Interconversion of glyceraldehyde-3-phosphate and dihydroxyacetone phosphate Conversion of aldose to ketose enables all carbons to continue through glycolysis Figure 8.3 Glycolytic Pathway Aldolase Triose Phosphate Isomerase

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Section 8.1: Glycolysis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Reactions of the Glycolytic Pathway Continued In Step 2 (reactions 6-10), each reaction occurs in duplicate 6. Oxidation of glyceraldehyde-3-phosphate Creates high-energy phosphoanhydride bond for ATP formation and NADH 7. Phosphoryl group transfer Production of ATP via substrate-level phosphorylation Figure 8.4 Glycolytic Pathway (Stage 2) Glyceraldehyde-3- phosphate dehydrogenase Phosphoglycerate Kinase

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Section 8.1: Glycolysis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Reactions of the Glycolytic Pathway Continued 8. Interconversion of 3-phosphoglycerate and 2-phosphoglycerate First step in formation of phosphoenolpyruvate (PEP) 9. Dehydration of 2-phosphoglycerate Production of PEP, which has a high phosphoryl group transfer potential ( tautomerization ), locks it into the highest energy form Figure 8.4 Glycolytic Pathway (Stage 2) Phosphoglycerate Mutase Enolase

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Section 8.1: Glycolysis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Reactions of the Glycolytic Pathway Continued 10. Synthesis of pyruvate Formation of pyruvate and ATP Produces a net of 2 ATP, 2 NADH, and 2 pyruvate Figure 8.4 Glycolytic Pathway (Stage 2) Pyruvate Kinase

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Section 8.1: Glycolysis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press The Fates of Pyruvate Pyruvate is an energy-rich molecule Under aerobic conditions, pyruvate is converted to acetyl- CoA for use in the citric acid cycle and electron transport chain Figure 8.6 The Fates of Pyruvate

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Section 8.1: Glycolysis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press The Fates of Pyruvate Continued Under anaerobic conditions pyruvate can undergo fermentation: alcoholic or homolactic Regenerates NAD + so glycolysis can continue Figure 8.7 Recycling NADH During Anaerobic Glycolysis

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Section 8.1: Glycolysis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Energetics of Glycolysis In red blood cells, only three reactions have significantly negative D G values Figure 8.8 Free Energy Changes During Glycolysis in Red Blood Cells

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Section 8.1: Glycolysis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Regulation of Glycolysis The rate of the glycolytic pathway is controlled by three allosteric enzymes: Hexokinase PFK-1 Pyruvate kinase Allosteric enzymes are sensitive indicators of a cell’s metabolic state regulated locally by effector molecules The hormones glucagon and insulin also regulate glycolysis

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Section 8.1: Glycolysis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Regulation of Glycolysis Continued High AMP concentrations activate PFK-1 and pyruvate kinase Fructose-2,6-bisphosphate, produced via hormone- induced covalent modification of PFK-2, activates PFK-1 Accumulation of fructose-1,6-bisphosphate activates PFK-1 providing a feed forward mechanism

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Section 8.2: Gluconeogenesis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Figure 8.9 Carbohydrate Metabolism: Gluconeogenesis and Glycolysis

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Section 8.2: Gluconeogenesis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Figure 8.9 Carbohydrate Metabolism: Gluconeogenesis and Glycolysis

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Section 8.2: Gluconeogenesis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Gluconeogenesis is the formation of new glucose molecules from precursors primarily in the liver Precursors include: lactate, pyruvate, and a - keto acids Gluconeogenesis Reactions Reverse of glycolysis except the three irreversible reactions

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Section 8.2: Gluconeogenesis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Gluconeogenesis Reactions Continued Three bypass reactions: 1. Synthesis of phosphoenolpyruvate (PEP) via the enzymes pyruvate carboxylase and pyruvate carboxykinase 2. Conversion of fructose-1,6-bisphosphate to fructose-6-phosphate via the enzyme fructose-1,6-bisphosphatase 3. Formation of glucose from glucose-6-phosphate via the liver and kidney-specific enzyme glucose-6-phosphatase (why only in kidney and liver?)

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Section 8.2: Gluconeogenesis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Gluconeogenesis Substrates Three of the most important substrates for gluconeogenesis are: 1. Lactate- released by skeletal muscle from the Cori cycle After transfer to the liver lactate is converted to pyruvate then to glucose 2. Glycerol- a product of fat metabolism Figure 8.10 Cori Cycle

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Section 8.2: Gluconeogenesis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Gluconeogenesis Substrates Continued 3. Alanine - generated from pyruvate in exercising muscle Alanine is converted to pyruvate then glucose in the liver Figure 8.11 The Glucose Alanine Cycle

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Section 8.2: Gluconeogenesis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Gluconeogenesis Regulation Substrate availability Hormones (e.g., cortisol and insulin) Figure 8.12 Allosteric Regulation of Glycolysis and Gluconeogenesis

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+ Section 8.2: Gluconeogenesis From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Gluconeogenesis Regulation Continued Allosteric enzymes (pyruvate carboxylase , pyruvate carboxykinase , fructose-1,6-bisphosphatase, and glucose-6-phosphatase) Figure 8.12 Allosteric Regulation of Glycolysis and Gluconeogenesis

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Regulation of gluconeogenesis Substrate cycle Substrate cycles decrease the net flux through the cycle, and provide a check point for regulation of the flux. Glucagon hormone

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Regulation of Glycogen Metabolism by hormones Insulin, glucagon, epinephrine After “fest” glucose level in blood increase, insulin is then released from pancreas. Insulin increases the transportation rate of glucose into muscles and fat tissues. During “fasting” glucose level in blood decrease and glucagon is released by the pancreatic cells. It stimulates glycogen degradation in liver. Epinephrine (adrenaline) is released in response to “fight-or-flight” situation, or a sudden need for energy situation. It stimulates glycogen degradation, and glycolysis in muscle. Its increased levels are associated with increase of glucose released by liver into blood.

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Section 8.3: Pentose Phosphate Pathway From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Pentose Phosphate Pathway Alternate glucose metabolic pathway Products are NADPH and ribose-5-phosphate Two phases: oxidative and nonoxidative Figure 8.13a The Pentose Phosphate Pathway (oxidative) Glucose-6-phosphate dehydrogenase Gluconolactonase

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Pentose Phosphate Pathway: Oxidative Three reactions Results in ribulose-5-phosphate and two NADPH NADPH is a reducing agent used in anabolic processes Figure 8.13b The Pentose Phosphate Pathway (oxidative) Section 8.3: Pentose Phosphate Pathway 6-phosphogluconate dehydrogenase

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Pentose Phosphate Pathway: Nonoxidative Produces important intermediates for nucleotide biosynthesis and glycolysis Ribose-5-phosphate Glyceraldehyde-3-phosphate Fructose-6-phosphate Figure 8.13b The Pentose Phosphate Pathway (nonoxidative) Section 8.3: Pentose Phosphate Pathway

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Pentose Phosphate Pathway If the cell requires more NADPH than ribose molecules, products of the nonoxidative phase can be shuttled into glycolysis Figure 8.14 Carbohydrate Metabolism: Glycolysis and the Phosphate Pathway Section 8.3: Pentose Phosphate Pathway

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Section 8.4: Metabolism of Other Important Sugars From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Fructose, mannose, and galactose are also important sugars for vertebrates Most common sugars found in oligosaccharides besides glucose Figure 8.15 Carbohydrate Metabolism: Galactose Metabolism

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Section 8.4: Metabolism of Other Important Sugars From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Fructose Metabolism Second to glucose in the human diet Can enter the glycolytic pathway in two ways: Through the liver (multi-enzymatic process) Muscle and adipose tissue ( hexokinase )

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Section 8.4: Metabolism of Other Important Sugars Figure 8.15 Carbohydrate Metabolism: Other Important Sugars

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Glycogenesis Synthesis of glycogen, the storage form of glucose, occurs after a meal Requires a set of three reactions (1 and 2 are preparatory and 3 is for chain elongation): 1 . Synthesis of glucose-1-phosphate ( G1P ) from glucose-6-phosphate by phosphoglucomutase 2. Synthesis of UDP-glucose from G1P by UDP-glucose phosphorylase Section 8.5: Glycogen Metabolism

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Glycogenesis Continued 3. Synthesis of Glycogen from UDP-glucose requires two enzymes: Glycogen synthase to grow the chain Figure 8.16 Glycogen Synthesis Section 8.5: Glycogen Metabolism Glycogen synthase

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Branching enzyme Section 8.5: Glycogen Metabolism From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Glycogenesis Continued Branching enzyme Amylo - a (1,4 1,6)- glucosyl transferase creates a (1,6) linkages for branches Figure 8.16 Glycogen Synthesis a (1,6) Glycosidic Linkage is formed

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Glycogenolysis Glycogen degradation requires two reactions: 1. Removal of glucose from nonreducing ends (glycogen phosphorylase ) within four glucose of a branch point Section 8.5: Glycogen Metabolism

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Figure 8.17 Glycogen Degradation Section 8.5: Glycogen Metabolism

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Section 8.5: Glycogen Metabolism Figure 8.18 Glycogen Degradation via Debranching Enzyme Glycogenolysis Cont. Glycogen degradation requires two reactions: 2. Hydrolysis of the a (1,6) glycosidic bonds at branch points by amylo - a (1,6)- glucosidase ( debranching enzyme) Amylo- a (1,6)-glucosidase Amylo- a (1,6)-glucosidase

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Section 8.5: Glycogen Metabolism Figure 8.18 Glycogen Degradation via Debranching Enzyme Amylo- a (1,6)-glucosidase

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Regulation of Glycogen Metabolism Carefully regulated to maintain consistent energy levels Regulation involves insulin , glucagon , epinephrine , and allosteric effectors Section 8.5: Glycogen Metabolism Figure 8.20 Major Factors Affecting Glycogen Metabolism

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From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Figure 8.20 Major Factors Affecting Glycogen Metabolism Section 8.5: Glycogen Metabolism Glucagon activates glycogenolysis Insulin inhibits glycogenolysis and activates glycogenesis Epinephrine release activates glycogenolysis and inhibits glycogenesis

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Biochemistry in Perspective From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Catabolic pathways with a turbo step are optimized and efficient Energy is fed back into the system to accelerate the fuel input step Figure 8A Glycolysis and the Turbo Jet Engine

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Maintenance of glucose levels in mammalians Glucose in blood between 3 mM and 10 mM The liver regulates the distribution of dietary fuel and supplies fuel from its own reserves when dietary supplies are exhausted

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George Cahill studied utilization of glucose (1960) Phase 1 : Glucose enters liver, and is used by most tissues as primary fuel. Pancreas secretes insulin, which stimulates glucose uptake by muscle and fat tissues. Excess of glucose is stored as glycogen in liver and muscle cells. Phase 2 : The liver glycogen is consumed to maintain the glucose level in the blood. In the muscle, glycogen is metabolized to lactate to produce ATP for contraction, and the lactate is transported to other tissues as a fuel or for gluconeogenesis (in liver). Phase 3 : Liver glycogen is depleted, and the only source of glucose in the blood is gluconeogenesis in the liver, using lactate, glycerol and alanine. Fatty acids in the fat tissues become the alternate fuel for most of the tissues.

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