Chapter 14.1 and 14.2: Glycolysis and Feeder Pathways

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Chapter 14.1 and 14.2: Glycolysis and Feeder Pathways. CHEM 7784 Biochemistry Professor Bensley. CHAPTER 14.1 and 14.2 Glycolysis. Today’s Objectives : To learn and understand the. Process of harnessing energy from glucose via glycolysis - PowerPoint PPT Presentation

Text of Chapter 14.1 and 14.2: Glycolysis and Feeder Pathways

  • Chapter 14.1 and 14.2: Glycolysis and Feeder PathwaysCHEM 7784BiochemistryProfessor Bensley

  • CHAPTER 14.1 and 14.2 GlycolysisProcess of harnessing energy from glucose via glycolysisVarious pathways by which carbohydrates other than glucose enter glycolysis Todays Objectives: To learn and understand the

  • Central Importance of GlucoseGlucose is an excellent fuelGlucose is a versatile biochemical precursorFour major pathways of glucose utilization

  • Glycolysis: The Big PictureAnaerobic process carried out by all cells but at different ratesConverts hexose to two pyruvatesGenerates 2 ATP and 2 NADHFor certain cells in the brain and eye, glycolysis is the only ATP generating pathway

    Glucose + 2 ADP + 2 NAD+ + 2Pi

    2 Pyruvate + 2 ATP + 2 NADH + 2 H+ + 2H20

  • Glycolysis: ImportanceGlycolysis is a sequence of ten enzyme-catalyzed reactions by which glucose is converted into pyruvate

    Two phases: First phase converts glucose to two G-3-P Second phase produces two pyruvate molecules

    Three possible fates for pyruvate

  • Glycolysis: The Preparatory Phase

  • Glycolysis: The Payoff Phase

  • STEP 1 - The Hexokinase ReactionThe first step, phosphorylation of glucose, is catalyzed by hexokinase in eukaryotes, and by glucokinase in prokaryotesThis process uses the energy of ATP

  • STEP 2 - Phosphohexose IsomerizationAn aldose can isomerize into ketose via an enediol intermediateOverall Glucose-6-Phosphate is converted to Fructose-6-Phosphate

  • STEP 3 - The Second Priming Reaction; The First Commitment This is an irreversible stepThe product, fructose 1,6-bisphosphate is committed to become pyruvate and yield energy

  • STEP 4 - Aldolases Cleave 6-Carbon Sugars Step four is the cleavage of Fructose 1,6-Bisphosphate

  • STEP 5 - Triose Phosphate Interconversion DAP is converted enzymatically to GAP

  • STEP 6 - Glyceraldehyde 3-Phosphate Dehydrogenase Reaction First step in the Payoff Phase of GlycolysisFirst energy-yielding step in glycolysis

  • STEP 7 - First Substrate-Level Phosphorylation1,3-bisphosphoglycerate is a high-energy compound that can donate the phosphate group to ADP to make ATP

  • STEP 8 - Conversion of 3-Phosphoglycerate to 2-PhosphoglycerateThis is a reversible isomerization reaction

  • Mechanism of the Phosphoglycerate Mutase Reaction

  • STEP 9 - Dehydration of 2-PhosphoglycerateThe goal here is to create a better phosphoryl donorLoss of phosphate from 2-phosphoglycerate would merely give a secondary alcohol with no further stabilization

  • STEP 10 - Second Substrate-Level Phosphorylation but loss of phosphate from phosphoenolpyruvate yields an enol that tautomerizes into ketone

  • Feeder Pathways for Glycolysis

    FIGURE 14-1 Major pathways of glucose utilization. Although not the only possible fates for glucose, these four pathways are the most significant in terms of the amount of glucose that flows through them in most cells.**FIGURE 14-2a The two phases of glycolysis. For each molecule of glucose that passes through the preparatory phase (a), two molecules of glyceraldehyde 3-phosphate are formed; both pass through the payoff phase (b). Pyruvate is the end product of the second phase of glycolysis. For each glucose molecule, two ATP are consumed in the preparatory phase and four ATP are produced in the payoff phase, giving a net yield of two ATP per molecule of glucose converted to pyruvate. The numbered reaction steps are catalyzed by the enzymes listed on the right, and also correspond to the numbered headings in the text discussion. Keep in mind that each phosphoryl group, represented here as P, has two negative charges (PO32).*FIGURE 14-2b The two phases of glycolysis. For each molecule of glucose that passes through the preparatory phase (a), two molecules of glyceraldehyde 3-phosphate are formed; both pass through the payoff phase (b). Pyruvate is the end product of the second phase of glycolysis. For each glucose molecule, two ATP are consumed in the preparatory phase and four ATP are produced in the payoff phase, giving a net yield of two ATP per molecule of glucose converted to pyruvate. The numbered reaction steps are catalyzed by the enzymes listed on the right, and also correspond to the numbered headings in the text discussion. Keep in mind that each phosphoryl group, represented here as P, has two negative charges (PO32).

    ****FIGURE 14-4 (part 1) The phosphohexose isomerase reaction. The ring opening and closing reactions (steps 1 and 4) are catalyzed by an active-site His residue, by mechanisms omitted here for simplicity. The proton (pink) initially at C-2 is made more easily abstractable by electron withdrawal by the adjacent carbonyl and nearby hydroxyl group. After its transfer from C-2 to the active-site Glu residue (a weak acid), the proton is freely exchanged with the surrounding solution; that is, the proton abstracted from C-2 in step 2 is not necessarily the same one that is added to C-1 in step 3.*FIGURE 14-4 (part 2) The phosphohexose isomerase reaction. The ring opening and closing reactions (steps 1 and 4) are catalyzed by an active-site His residue, by mechanisms omitted here for simplicity. The proton (pink) initially at C-2 is made more easily abstractable by electron withdrawal by the adjacent carbonyl and nearby hydroxyl group. After its transfer from C-2 to the active-site Glu residue (a weak acid), the proton is freely exchanged with the surrounding solution; that is, the proton abstracted from C-2 in step 2 is not necessarily the same one that is added to C-1 in step 3.

    ***FIGURE 14-5 (part 1) The class I aldolase reaction. The reaction shown here is the reverse of an aldol condensation. Note that cleavage between C-3 and C-4 depends on the presence of the carbonyl group at C-2. A and B represent amino acid residues that serve as general acid (A) or base (B).*FIGURE 14-5 (part 2) The class I aldolase reaction. The reaction shown here is the reverse of an aldol condensation. Note that cleavage between C-3 and C-4 depends on the presence of the carbonyl group at C-2. A and B represent amino acid residues that serve as general acid (A) or base (B).*FIGURE 14-5 (part 3) The class I aldolase reaction. The reaction shown here is the reverse of an aldol condensation. Note that cleavage between C-3 and C-4 depends on the presence of the carbonyl group at C-2. A and B represent amino acid residues that serve as general acid (A) or base (B).*FIGURE 14-5 (part 4) The class I aldolase reaction. The reaction shown here is the reverse of an aldol condensation. Note that cleavage between C-3 and C-4 depends on the presence of the carbonyl group at C-2. A and B represent amino acid residues that serve as general acid (A) or base (B).*FIGURE 14-5 (part 5) The class I aldolase reaction. The reaction shown here is the reverse of an aldol condensation. Note that cleavage between C-3 and C-4 depends on the presence of the carbonyl group at C-2. A and B represent amino acid residues that serve as general acid (A) or base (B).***FIGURE 14-7 (part 1) The glyceraldehyde 3-phosphate dehydrogenase reaction.*FIGURE 14-7 (part 2) The glyceraldehyde 3-phosphate dehydrogenase reaction.*FIGURE 14-7 (part 3) The glyceraldehyde 3-phosphate dehydrogenase reaction.*FIGURE 14-7 (part 4) The glyceraldehyde 3-phosphate dehydrogenase reaction.*FIGURE 14-7 (part 5) The glyceraldehyde 3-phosphate dehydrogenase reaction.***FIGURE 14-8 (part 1) The phosphoglycerate mutase reaction.

    *FIGURE 14-8 (part 2) The phosphoglycerate mutase reaction.**FIGURE 14-10 Entry of dietary glycogen, starch, disaccharides, and hexoses into the preparatory stage of glycolysis.

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