6F. What conformational state is stabilized by y in ATP synthase? Why might achieving this state require energy input from the PMF?

24. Consider the figure below, which is an alternate way to depict the energy changes occurring during a reaction from Substrate (S) to Product (P), when uncatalyzed (curve A) and when catalyzed by an enzyme (curve B). Note that curve B is not the same way we modeled an enzyme-catalyzed reaction in class; this model is a different, perhaps slightly more realistic, way of conceptualizing the energy changes over the course of a reaction than what we did in class. S and ES represent the transition states for reaction of the free substrate (S) or the enzyme-substrate complex (ES). T T activation energy for uncatalyzed reaction EST S edhosob nohtum od bluo woH abiow yedio 2 wwolaixa-y odi no vaigin oroda dapng odt ni o nfog) r gibadhoa P B ES EP progress of reaction activation energy for catalyzed reaction a) Explain briefly why, in curve B, the energy state of the enzyme-substrate complex is less than the energy state of the substrate alone. b) Suppose the enzyme in the diagram was mutated…

23. An important step in glycolysis is the formation of ATP and pyruvate from phosphoenol-pyruvate (PEP) and ADP. PEP ADP pyruvate+ATP The equilibrium constant (Keq) for this reaction is approximately 2.5x10°. Calculate standard free energy change (AG°') for this reaction. Show your work. onege b. Is the reaction exergonic or endergonic at standard conditions? If, at equilibrium, the concentrations of ADP and ATP are 0.2 mM and 2.0 mM, respectively, what is the equilibrium concentration ratio of [pyruvate] to [PEP]? Show your work. с.

4. The reaction shown below is part of the glycolytic pathway. The standard free energy change for this reaction is +0.4 kcal'mol. Glucose-6-phosphate (G6P) > Fructose-6-phosphate (F6P) A) What is K,' for this reaction at 25°C?

7. Flow of carbon atoms. What is the fate of the radioac- tive label when each of the following compounds is added to a cell extract containing the enzymes and cofac- tors of the glycolytic pathway, the citric acid cycle, and the pyruvate dehydrogenase complex? (The ¹4C label is printed in red.) (a) (c) H3C H3C O C. O C. COO COO- (b) (d) H3C H₂C O C. O C. (e) Glucose 6-phosphate labeled at C-1. COO™ S-COA

The following structure is ATP synthase. Which of the following statements is NOT true for the ATP synthase? B b2 6 a В a Y E H+ α C10 B ATP ADP + Pi N side 800000 P side

6

draw 3 allosteric enzyme curves for glycogen synthesis in the presence of high AMP, high NADH, and no regulators on 1 graph.

+ Explain why a strain of yeast with a defect in the enzyme alcohol dehydrogenase can grow well under aerobic conditions, but not under anaerobic conditions. The yeast strain grows well when aerobic because acetaldehyde is quickly converted to lactate. The yeast strain uses CO₂ to generate NAD+ when aerobic, but GAPDH needs NADH when anaerobic. The yeast strain grows equally well under aerobic and anaerobic, but polyphenol is lethal to this strain. The yeast strain cannot oxidize NADH to generate NAD+ for the GAPDH reaction when anaerobic. The yeast strain needs to generate ethanol in order to stimulate the PFK- 1 reaction when anaerobic.

3. One indication of the relative importance of various ATP-producing pathways is the Vmax of certain enzymes of these pathways. The values of Vmax of several enzymes from the pectoral muscles (chest muscles used for flying) of pigeon and pheasant are listed below. Vmax (umol substrate/min/g tissue) Enzyme Pigeon Pheasant Hexokinase 3.0 2.3 Glycogen phosphorylase Phosphofructokinase-1 Citrate synthase Triacylglycerol lipase 18.0 120.0 143.0 24.0 100.0 15.0 0.07 0.01 b. Compare oxygen consumption in the two birds.