Biochemistry - I Mondays and Wednesdays 9:0-10:4 AM (MR-107) SPRING 017 Lecture 1 Based on Profs. Kevin Gardner & Reza Khayat 1
utline Bioenergetics Fates of glucose Glycolysis Feeder pathways for glycolysis Why learn about Glycolysis and Gluconeogenesis? Capable of supplying a huge array of metabolites used by many cellular processes, biofuels, high rate of glycolysis in tumors, lactose intolerance etc.
Bioenergetics In aerobic organisms, the ultimate electron acceptor in the oxidation of carbon is The oxidation product is C and the reduction product is The more reduced a carbon is, the more exergonic (energy releasing) its oxidation will be Rapid but reduced amount of energy Slow but tremendous amount of energy
Bioenergetics - Two elpful Pointers Text uses SI units of energy: joules & kilojoules 4.184 J = 1 cal 4.184 kj = 1 kcal = 1 dietary Cal note 1 Cal (dietary) = 1000 cal (chemical) 4
Adenosine Triphosphate (ATP) B B B PP P Rib A A A ø Mg ø Adenine MgATP Reactions written with substrate as ATP, but true substrate is Mg/ATP - Mg + shields the negative charge of terminal phosphates and allows for nucleophilic attack by enzyme or other substrates Enzymes that bind ATP -4 need Mg + present ATP -> ADP + Pi has ΔG of -0. kj/mol each of us has about 0. mol of ATP at any given time cannot be stored, usually recycled ~00 cycles per day
Fates of Glucose The complete oxidation of glucose to carbon dioxide and water proceeds with a standard freeenergy change of -,840 kj/mol Glycolysis is first part of this, handling oxidation to pyruvate 6
verview of Glycolysis ccurs in cytoplasm 7
Terminology Note that you ll see plenty of ΔG ( delta G prime naught = standard free energy change ) values on next slides; remember that those are determined at standard conditions (p 7.0, 1 mm MgCl, 1M other reactantsthese values are obviously not at equilibrium! As such, ΔG values tell you which direction a reaction will spontaneously proceed in, and how far this is from equilibrium, when at standard conditions! ΔG values ( actual free energy change ) at any specific condition requires knowledge of actual reactant & product concentrations: Read section 1.1 G RT ln K n. eq aa bb cc dd G G RT ln [C]c [D] d [A] a [B] b terms in red are those actuall Mass action ratio 8
Preparatory Phase - R1 6 C P 4 1 Glucose 6-phosphate Reaction 1. Glucose is phosphorylated for subsequent phases and the reaction is irreversible under conditions in the cell Kinase: Transfers gamma-phosphate from ATP to a substrate molecule. 9
Preparatory Phase - R 6 C P 4 1 Glucose 6-phosphate Reaction. The enzyme catalyses the reversible isomerization of an aldose to a ketose. Isomerase: facilitate intramolecular rearrangement. 10
Preparatory Phase - R 6 C P 4 1 Glucose 6-phosphate Glucose 6-phosphate 4 6 C P 1 Fructose 6-phosphate 6 C P 4 Binding and Dissociation 1 opening of and closing 4 the ring of the ring 1 C Phosphohexose isomerase B: 1 C C C 4 C C + 6 C P B C C + C C Proton abstraction by active-site Glu (B:) leads to cis-enediol formation. cis-enediol intermediate B: C C C C C General acid catalysis by same C C P Glu facilitates C P formation of fructose 6- phosphate. nce protonated, a general base (B:) can act as a general acid (B) The general base is Glu. 11
Preparatory Phase - R 6 C P 4 1 Glucose 6-phosphate Reaction. Called PFK1 to distinguish it from PFK, that catalyses the formation of fructose, 6-bisphosphate from fructose 6-phosphate in a separate pathway. Large negative ΔG favors product formation, and reaction is practically irreversible in cell. Compensates for reaction having positive ΔG. 1
Preparatory Phase - R4 6 C P 4 1 Glucose 6-phosphate Reaction 4. Aldolase catalyses a fully reversible reaction that converts a 6C compound into two different C compounds. Note ΔG 1
Preparatory Phase - R 6 C P 4 1 Reaction. nly glyceraldehyde -phosphate (GP) is directly degraded in the subsequent payoff steps of glycolysis. Rapid interconversion between GP & DAP. 14
Cleave between C and C4 R4 & R 1
Payoff Phase - R6 6 C P 4 1 Glucose 6-phosphate Reaction 6. The first step in the payoff phase leads to the formation of a high energy acyl phosphate and eventually formation of ATP. This acyl phosphate is highly reactive, and hence the positive ΔG. This product forms because of the low concentration NAD + in cells (e.g. it is kinetically driven rather than thermodynamically) 16
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Payoff Phase - R7 6 C P 4 1 ATP generated! Reaction 7. The enzyme transfers the high energy phosphoryl group to ADP forming ATP. The enzyme is named for the reverse direction, as the reaction is reversible. The large negative ΔG pays for the prior reactions thermodynamically. 18
Payoff Phase - R8 6 C P 4 1 Glucose 6-phosphate Reaction 8. The enzyme catalyzes the reversible shift of the phosphoryl group between the C- and C- of glycerate. 19
Payoff Phase - R9 6 C P 4 1 Glucose 6-phosphate Reaction 9. This enolase reaction generates a high energy compound, phosphoenolpyruvate, that will spontaneously release its phosphate. 0
Payoff phase - R10 6 C P 4 1 Glucose 6-phosphate ATP generated! Reaction 10. The transfer of the phosphoryl group to ADP forms ATP and completes glycolysis. This is another substrate-level phosphorylation (like step 7). The product pyruvate tautomerizes rapidly and nonenzymatically to its preferred keto form, this tautomerization also drives the reaction forward since it removes the product. 1
verall Balance Sheet Glucose NAD 88n pyruvate NAD (14 ) G 1 146 kj/mol ADP P i 88n ATP (14 ) G (0. kj/mol) 61.0 kj/mol G s G 1 G 146 kj/mol 61 kj/mol 8 kj/mol Glucose ATP NAD 4ADP P i 88n pyruvate ADP NAD 4ATP Glycolysis is essentially an irreversible process The complete oxidation of glucose to carbon dioxide and water proceeds with a standard free-energy change of -,840 kj/mol (remaining portion of reaction occurs in oxidative phosphorylation)
Why Many Phosphorylated Intermediates? All products/reactants after glucose are phosphorylated Glucose is transported into cell via facilitated passive diffusion by a carrier (GLUT). This carrier is reversible. Phosphorylation changes charge and structure of glucose. This inhibits its transport through GLUT and out of cell. Energy released in hydrolysis of phosphodiester bond of ATP is partially retained in the phosphodiester bond of a product/ reactant. igh energy intermediates (BPG and PEP) can transfer phosphate to ADP to make ATP. Binding energy of phosphate intermediates to enzymes is increased because of phosphate. This helps drive catalysis.
Feeder Pathways for Glycolysis Many carbohydrates are catabolized through glycolysis Some are converted to D-glucose, others are catabolized to intermediates of glycolysis The most significant are: Monosaccharides: fructose, mannose, and galactose Disaccharides: maltose, lactose, trehalose, and sucrose 4