Glycogen Synthesis - Storing a Ready-reserve of Carbohydrate

OUTLINE: Introduction and review Transport Glycogenolysis Glycolysis Other sugars Pasteur: Anaerobic vs Aerobic Fermentations Pyruvate Krebs’ Cycle Oxidative Phosphorylation ANABOLISM I: Carbohydrates Carbon Assimilation – Calvin Cycle Stage One – Rubisco Carboxylase Know mechanism Oxygenase Glycolate cycle Stage Two – making sugar Stage Three - remaking Ru 1,5P2 Exam-1 material Exam-2 material Electron transport Chemiosmotic theory: Phosphorylation Fat Catabolism Fatty acid Catabolism Overview and regulation Calvin cycle connections to biosynthesis C4 versus C3 plants Kornberg cycle - glyoxylate Exam-3 material Mobilization from tissues (mostly adipose) Activation of fatty acids Transport; carnitine Oxidation: b-oxidation, 4 steps: Protein Catabolism Carbohydrate Biosynthesis in Animals precursors Cori cycle Amino-Acid Degradation Dealing with the nitrogen; Urea Cycle Dealing with the carbon; Seven Families Nucleic Acid & Nucleotide Degradation Gluconeogenesis reversible steps irreversible steps – four PHOTOSYNTHESIS: energetics 2-steps to PEP mitochondria Pyr carboxylase-biotin PEPCK FBPase G6Pase Overview of Photosynthesis Key experiments: Light Reactions energy in a photon pigments HOW Light absorbing complexes-”red-drop experiment” Reaction center Photosystems (PS) PSII – oxygen from water splitting PSI – NADPH Proton Motive Force – ATP Overview of light reactions Glycogen Synthesis UDP-Glc Glycogen synthase branching Pentose-Phosphate Pathway Regulation of Carbohydrate Metabolism Anaplerotic reactions Gluconeogenesis Why do we need glucose? RECALL: PEP • Physiologically necessary: Brain, nervous system, and red blood cells generate ATP ONLY from glucose. • When we can’t get it from pyruvate, amino acids are utilized, which allows generation of glucose when glycogen stores are depleted: – – – during starvation during vigorous exercise can generate glucose from amino acids, but not fatty acids DG°’ = –9 kcal/mol • Gluconeogenesis Costs 4 ATP, 2 GTP, and 2 NADH. Net reaction: 2 Pyruvate + 4 ATP + 2 GTP + 2 NADH + 2 H+ + 4 H2O à Glucose + 4 ADP + 2 GDP + 6 Pi + 2 NAD+ 1 Glycogen Synthesis Storing a ready-reserve of carbohydrate Glycogen Synthesis • Synthesis of glycogen requires two enzymes, whereas glycogen degradation, only used phosphorylase. Both pathways use a-phosphoglucomutase; the start and end junction is Glc 1-P. • Blood glucose must be: – – – – Phosphorylated: Glc à Glc-6-P Then converted: Glc 6-P à Glc 1-P Activated with UDP (UDP-Glc is the precursor) Added to glycogen 2 Glycogen Synthesis Glycogen Is Synthesized by Glycogen Synthase Glycogenin Starts a New Glycogen Chain Takes 2 “ATPs” to put Glc into polymer (Glc1P & UDP-Glc), but get 33 ATP of potential energy. Glycogen Synthesis General Structure of a Glycogen Particle Each chain has average of 2 1à6 branches fifth – 12th tier (last tier is unbranched) Calculate the number of Glc residues in a glycogen molecule: 29 – 212 x 12-14 = 6,000–57,000 Glc per glycogen Exponent= number of (MW = 106 – 107) tiers Synthesis of Branches in Glycogen 3 Pentose Phosphate Pathway Providing reduced electrons and ribose Pentose Phosphate Pathway (oxidative) Fructose 6-phosphate Fru1,6P2 (Non-oxidative) Pentose Phosphate Pathway, sometimes called the pentosephosphate shunt, is linked to Glycolysis Because it provides for essential components of these biomolecules, we will consider it part of anabolism. 4 Pentose Phosphate Pathway Dr. Kornberg: Pentose Phosphate Pathway (oxidative) (Non-oxidative) Pentose Phosphate Pathway, sometimes called the pentosephosphate shunt, is linked to Glycolysis Because it provides for essential components of these biomolecules, we will consider it part of anabolism. 5 Pentose Phosphate Pathway • Included in Anabolism because it provides the NADPH needed for so many biosynthetic reduction reactions, as well as the synthesis of pentoses. • But, can also be used for a shunt in the catabolism of Glc 6-P. • The main products are NADPH and ribose 5-phosphate (Rib 5-P). • Oxidative Phase oxidizes Glc 6-P to make NADPH • Non-oxidative Phase re-cycles pentoses to hexoses if not needed for biosynthesis. Uses of Pentose Phosphate Pathway (PPP): ØNADPH is an electron donor. – reductive biosynthesis of fatty acids and steroids – reductive biosynthesis of amino acids and nucleotide bases – repair of oxidative damage ØRibose 5-phosphate is a biosynthetic precursor of nucleotides. – used in DNA and RNA synthesis – or synthesis of some coenzymes Pentose Phosphate Pathway Oxidative Phase Generates NADPH and a Pentose Allosteric inhibition by product NADPH Mechanism lactone 6 Pentose Phosphate Pathway 5 Mechanism Overall 4 steps of oxidative branch of PPP Mechanism Pentose Phosphate Pathway (aldose) Ru 5-P (ketose) (ketose) Phosphogluco isomerase 3C′s 2C′s (aldose) Phosphogluco isomerase (ketose) (ketose) (aldose) (aldose) 2C′s (ketose) (aldose) Non-oxidative Phase Interconverts Rib 5-P to form Glc 6-P • No ATP is used in the non-oxidative phase. • Complete conversion of ribose-5-phosphate to glucose-6phosphate requires 6 Rib 5-P (30 carbons) to make 5 Glc 6-P (30 carbons). 7 Pentose Phosphate Pathway 6 2 6 (aldose) Ru 5-P (ketose) (ketose) 2 2 2C′s 3C′s 2 2 2 4 (ketose) (aldose) 5 4 2 Phosphogluco isomerase (aldose) Phosphogluco isomerase 2 1 (ketose) (aldose) 2C′s 2C′s 2 (aldose) (ketose) Non-oxidative Phase Interconverts Rib 5-P to form Glc 6-P • No ATP is used in the non-oxidative phase (completely reversible. • Complete conversion of ribose-5-phosphate to glucose-6phosphate requires 6 Rib 5-P (30 carbons) to make 5 Glc 6-P (30 carbons). Pentose Phosphate Pathway (ketose) (aldose) (aldose) (ketose) Transaldolase Mechanism CH2OH : TPP H+ | Protonated Schiff base (e– sink) E-NH2 + Ketose ⇌ E–N=C | HOCH | HC–O-H | R :B Enamine carbanion This carbanion is protonated in aldolase In transaldolase, it makes a nucleophilic attack on the aldehyde of the secondsubstrate aldose. ℗ TPP 8 Pentose Phosphate Pathway NADPH Regulates Partitioning into Glycolysis versus Pentose Phosphate Pathway • Used in tissues needing NADPH and ATP – ATP is low Dihydroxyacetonephosphate phosphate phosphate • Used in tissues requiring • Used in tissues more NADPH than Rib 5-P needing both Rib 5-P & NADPH – such as the liver and adipose tissue – ATP is plentiful • Used in tissues requiring more Rib 5-P than NADPH – such as the lymphocytes and fast growing tissues/cancer cells Pentose Phosphate Pathway Converting Cytosolic Electron Carriers (NADPH from PPP & NADH from glycolysis) to the Mitochondria Nicotinamide nucleotide transhydrogenase NADPH antiporter NADP+ Malate-Aspartate Shuttle • This more complicated shuttle is mostly present in liver, heart, and kidney. • It moves NADH & NADPH equivalents from cytosol to NADH & NADPH equivalents in the mitochondria. antiporter or NADPH 9 Regulation of Carbohydrate Metabolism Catabolism vs. Anabolism Gluconeogenesis Glycolysis versus Gluconeogenesis Glycolysis occurs mainly in the muscle and brain. • Opposing pathways that are both thermodynamically favorable: • Glycolysis: DG°’ = –35 kcal/mol • Gluconeogenesis: DG°’=–9 kcal/mol 7 PGI 6 5 Aldolase TIM 4 GAPDH 3 PGK 2 PGM 1 Enolase – operate in opposite direction • end product of one is the starting compound of the other • Seven Reversible reactions are used by both pathways. • Three ”glycolysis-specific” steps are reversed with Four “gluconeogenesis-specific” steps. Gluconeogenesis occurs mainly in the liver and kidney cortex. • Irreversible reactions of glycolysis must be bypassed in gluconeogenesis. – no ATP generated during gluconeogenesis; instead 6 ATPs and 2 NADH needed per Glc. – Some different enzymes results in the different pathways – differentially regulated to prevent a futile cycle 10 Catabolism vs. Anabolism Regulation of Carbohydrate Metabolism Gene controlled Glycogenolysis versus Glycogen Synthesis Catabolism Glycogen Glycogen Phosphorylase Glycogen Synthase Anabolism Phosphorylase Glycogen Synthase Hexokinase Glucose 6phosphatase Phosphofructokinase-1 Fructose 1,6bisphosphatase -1 Pyruvate Kinase – PEPCK – Pyruvate carboxylase UDP-Glc Glycolysis versus Gluconeogenesis UDP-glucose pyrophosphorylase Glc 1-P phosphoglucomutase • Regulated enzymes often correspond to points in the pathways that have the same substrate and product, but a different enzyme. • Also where there are junctions. • Can you name those enzymes? Acetyl-CoA Pyruvate Dehydrogenase Complex – Regulation of Carbohydrate Metabolism Regulation of Pyruvate Dehydrogenase Complex • Allosteric regulation by energy charge and substrate/product –ADP & pyruvate activates –ATP/NADH & acetyl-CoA inhibit • Regulated by reversible phosphorylation of E1 –phosphorylation: inactive –dephosphorylation: active • PDH kinase and PDH phosphatase are part of mammalian PDH complex. –Kinase is activated by ATP. • high ATP à phosphorylated PDH à less acetyl-CoA made • low ATP à kinase is less active and phosphoprotein phosphatase removes phosphate from PDH à more acetyl-CoA made 11 Catabolism vs. Anabolism Regulation of Carbohydrate Metabolism Gene controlled Glycogenolysis versus Glycogen Synthesis Catabolism Glycogen Glycogen Phosphorylase Glycogen Synthase Anabolism Phosphorylase Glycogen Synthase Hexokinase Glucose 6phosphatase Phosphofructokinase-1 Fructose 1,6bisphosphatase -1 Pyruvate Kinase – PEPCK – Pyruvate carboxylase UDP-Glc Glycolysis versus Gluconeogenesis UDP-glucose pyrophosphorylase Glc 1-P phosphoglucomutase • Regulated enzymes often correspond to points in the pathways that have the same substrate and product, but a different enzyme. • Also where there are junctions. • Can you name those enzymes? Acetyl-CoA Pyruvate Dehydrogenase Complex ✓ Regulation of Carbohydrate Metabolism Regulation of Pyruvate All tissues Kinase • Allosterically activated by fructose-1,6-bisphosphate – increase flow through glycolysis – Feed-forward activation • Allosterically inhibited by signs of abundant energy supply. –ATP –acetyl-CoA and long-chain fatty acids –alanine (enough amino acids) Liver only (under hormonal control) Inactivated by phosphorylation in response to signs of glucose depletion (low bloodglucoseàglucagon) (liver only) Glucose from liver is exported to the brain and other vital organs. This is not the only time we’ll see hormonal control of these pathways. 12 Regulation of Carbohydrate Metabolism Regulation of Pyruvate All tissues Kinase • Allosterically activated by fructose-1,6-bisphosphate – increase flow through glycolysis – Feed-forward activation • Allosterically inhibited by signs of abundant energy supply. –ATP –acetyl-CoA and long-chain fatty acids –alanine (enough amino acids) Liver only (under hormonal control) Inactivated by phosphorylation in response to signs of glucose depletion (low bloodglucoseàglucagon) (liver only) Glucose from liver is exported to the brain and other vital organs. This is not the only time we’ll see hormonal control of these pathways. 13