Glycogen Breakdown

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Glycogen Breakdown. Glycogen is cleaved by phosphate to give ________________________________________ Cleavage reaction is ______________________, not hydrolysis No _______ is involved in reaction Reaction is catalyzed by glycogen phosphorylase. Glycogen Breakdown. - PowerPoint PPT Presentation

Transcript of Glycogen Breakdown

  • Glycogen BreakdownGlycogen is cleaved by phosphate to give ________________________________________Cleavage reaction is ______________________, not hydrolysisNo _______ is involved in reactionReaction is catalyzed by glycogen phosphorylase

  • Glycogen BreakdownIn the second reaction, glucose-1-phosphate is isomerized to __________________________This reaction is catalyzed by phosphoglucomutase

    Complete breakdown requires debranching enzymes to degrade the ________________ linkages

  • Debranching Glycogen

  • How is Glycogen formed from Glucose?Not exact reversal of glycogen breakdown to glucoseGlycogen synthesis requires energyEnergy supplied by hydrolysis of ___________________Glucose-1-phosphate reacts with UTP to make UDPGPyrophosphate is also formedUDPG is then added to a growing chain of glycogen, catalyzed by glycogen _______________________

  • How is Glycogen formed from Glucose?Coupling of UDPG formation with hydrolysis of ____________________________ drives formation of UDPG to completion

  • Reaction Catalyzed by Glycogen Synthase

  • Control of Glycogen MetabolismGlycogen phosphorylase is a major control point in the synthesis and breakdown of glycogenGlycogen phosphorylase activity can be allosterically controlled, as well as, controlled through _________ modification

  • Control of Glycogen Metabolism (Contd)The activity of glycogen synthase is subject to the same type of covalent modification as glycogen phosphorylase, but the response is oppositeIn addition:Hormonal signals (glucagon or epinephrine) _______ its phosphorylationAfter phosphorylation, glycogen synthase becomes __________ at the same time the hormonal signal is activating phosphorylaseGlycogen synthase can be phosphorylated by several other enzymes including phosphorylase kinaseDephosphorylation is by phosphoprotein phosphatase

  • SummaryGlycogen is the storage form of glucose in animals, including humans. Glycogen releases glucose when energy demands are high

    Glucose polymerizes to form glycogen when the organism has no immediate need for the energy derived from glucose breakdown

    Glycogen metabolism is subject to several different control mechanisms, including covalent modification and allosteric effects

  • GluconeogenesisGluconeogenesis: pyruvate glucose Gluconeogenesis is __________________________ of glycolysis; that is, pyruvate to glucose does not occur by reversing the steps of glucose to pyruvateThree irreversible steps in glycolysis- Phosphoenolpyruvate to pyruvate + ATP- Fructose-6-phosphate to fructose-1,6-bisphosphate- Glucose to glucose-6-phosphateNet result of gluconeogenesis is reversal of these three steps, but by different __________________ and using different __________________

  • Oxaloacetate is an IntermediateIn first step, pyruvate is carboxylated to oxaloacetateRequires ________________ (CO2 carrier)Pyruvate carboxylase is subject to allosteric control; it is activated by _______________________

  • Gluconeogenesis (Contd)Next, decarboxylation of oxaloacetate is coupled with phosphorylation by ___________ to give PEP

    The net reaction of carboxylation/decarboxylation isPyruvate + ATP +GTP Phosphenolpyruvate + ADP + GDP + Pi

  • Pyruvate Carboxlyase Reaction

  • Role of Sugar PhosphatesOther different reactions in gluconeogenesis relative to glycolysis involve phosphate-ester bonds bound to sugar-hydroxyl groups being hydrolyzed

    G = -16.7kJ mol-1Fructose-1,6-bisphosphatase is an ________ enzyme, inhibited by AMP and activated by ATP

  • Role of Sugar Phosphates (Contd)Another reaction is the hydrolysis of glucose-6-phosphate to ___________ and _______

    Reaction also spontaneous (G = -13.8 kJ mol-1)Reaction catalyzed by glucose-6-phosphatase

  • Control of Carbohydrate MetabolismAllosteric control: fructose-2,6-bisphosphate (F2,6P)An allosteric ________ of phosphofructokinase (PFK)An allosteric ________ of fructose bisphosphate phosphatase (FBPase)High concentration of F2,6P stimulates __________; a low concentration stimulates ____________ Concentration of F2,6P in a cell depends on the balance between _________________ (catalyzed by phosphofructokinase-2) and _______________ (catalyzed by fructose bisphosphatase-2)Each enzyme is controlled by phosphorylation/dephosphorylation

  • Synthesis and Breakdown of F2,6P

  • Mechanisms of Metabolic Control

  • Substrate CyclingSubstrate cyclingopposing reactions can be catalyzed by different enzymes and each opposing enzyme or set of enzymes can be ________________________

    Fructose-6-Phosphate + ATP Fructose-1,6,-bisphosphate + ADP

    Fructose-1,6,-bisphosphate + ADP Fructose-6-Phosphate + PiBoth Reactions are exergonic, and the net reaction is

    ATP +H2O ADP + Pi

  • Organs Share Carbohydrate MetabolismThe Cori cycleUnder vigorous ____________ ____________, glycolysis in muscle tissue converts glucose to pyruvate; NAD+ is regenerated by reduction of pyruvate to lactateLactate from muscle is transported to the _________, reoxidized to pyruvate, and converted to glucoseThe liver shares the stress of vigorous exercise

  • The Cori Cycle

  • Control Points in Carbohydrate MetabolismFirst and last steps in glycolysis are major control points in glucose metabolism________________________ Inhibited by high levels of glucose 6-phosphateWhen glycolysis is inhibited through phosphofructokinase, glucose 6-phosphate builds up, shutting down hexokinase________________________ (PK) is an allosteric enzymeInhibited by ATP and alanineActivated by fructose-1,6-bisphosphate________________________ have 3 different subunitsM predominates in muscle, L in liver, and A in other tissuesNative PK is a tetramerLiver isoenzymes are subject to covalent modification

  • SummaryA number of control mechanisms operate in carbohydrate metabolism. These include allosteric effects, covalent modification, substrate cycles, and genetic control

    In the mechanism of substrate cycling, the synthesis and the breakdown of a given compound are catalyzed by two different enzymes

  • The Pentose Phosphate PathwayThe Pentose Phosphate Pathway (PPP) is an alternative to __________________, and differs in several waysIn glycolysis, ATP production is important, in PPP, _________________________________As the name implies, ____________ sugars, including ribose, are produced from glucoseOxidizing agent is NADP+; it is reduced to NADPH, which is a reducing agent in biosynthesesBegins with two oxidation steps (NADP+) to give ____________________________________Following this, a series of ___________________________ occur during which three-, four-, five-, six-, and seven-carbon monosaccharide phosphates are produced

  • The Pentose Phosphate Pathway

  • Control of the Pentose Phosphate PathwayThe carbon-shuffling reaction are catalyzed by:________________________ for the transfer of two-carbon units and________________________ for the transfer of three-carbon unitsControl of the PPP is maintained by:Glucose-6-phosphate (G6P) can be channeled into either glycolysis or the pentose phosphate pathwayG6P channeling into glycolysis, if ________________G6P channeling into the pentose phosphate pathway, if _________ or __________________ are needed

  • Group Transfer Reactions

  • Relationship between PPP and Glycolysis