7. When Pyruvate dehydrogenase complex (PDH) is phosphorylated, it is inactive. In cell A the PDH kinase enzyme is allosterically activated. In cell B the PDH kinase is allosterically inhibited. Use the table below to indicate which cell would fit each scenario. (4 points) Higher phosphorylated PDH Higher CO2 production Higher NADH/H production Higher O? consumed Cell A PDH Kinase is allosterically activated Cell B PDH Kinase is allosterically inhibited
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This means that when PDH is phosphorylated, it cannot carry out its function of converting pyruvate into acetyl-CoA. Show more…
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Pyruvate dehydrogenase is the entry point for the glycolytic product pyruvate into oxidative metabolism (the citric acid cycle and oxidative phosphorylation). Because it occupies such an important checkpoint in metabolism, it is tightly regulated. Determine whether the given conditions promote entry into oxidative metabolism or limit entry into oxidative metabolism. These abbreviations may be used: PDH is pyruvate dehydrogenase; PDK is pyruvate dehydrogenase kinase; PDP is pyruvate dehydrogenase phosphatase. Oxidative metabolism increases Oxidative metabolism is limited low O2 levels, inactive PDH high O2 levels, PDK inhibitor present high O2 levels, active PDP high O2 levels, PDK active low O2 levels, PDK active What is the fate of pyruvate (in a human) if a PDK inhibitor, such as dichloroacetate, is administered? It is processed to acetyl-CoA. It is processed to lactate. It is processed to ethanol.
Adi S.
The compound below is a transition state analog that binds to the pyruvate dehydrogenase enzyme complex (PDH) at the site for one of the five coenzymes used by the PDH. Binding is significantly tighter (inhibitor constant Ki < 5 x 10^10 M) than the naturally occurring coenzyme (inhibitor constant Ki < 1 x 10^-5 M), indicating it fits the active site. Binding results in the inactivation of the PDH. a) Which of the coenzymes required by the PDH does this molecular analog displace? List and draw the structure of this coenzyme. b) How does the transition state analog differ chemically from the naturally occurring coenzyme? c) Why would the chemical difference, described in part b, result in a loss of PDH enzyme activity? This can be illustrated by drawing the reactions; in words, or both:
1. Explain how the Pyruvate Dehydrogenase Complex is regulated by phosphorylation. In your answer, refer to the biological rationale for: Activation of PDH kinase by NADH Activation of PDH phosphatase by Calcium ions. Would you expect NAD+ or CoA-SH to affect the activity of the enzyme pyruvate dehydrogenase kinase? Explain. How is the PDH complex itself regulated allosterically? 2. Cell signaling can lead to short-term and long-term responses. Provide general examples of (i) a long-term change and (ii) a short-term change that occur after signaling molecules bind to a receptor on the cell surface. 3. In the epinephrine signaling pathway, Phosphorylase b (less active) is converted to Phosphorylase a (more active) by Glycogen phosphorylase kinase through the addition of a phosphate to serine 14. Explain in detail the importance of covalent modification in the control of this allosteric enzyme. 4. ATCase, a heterotropic allosteric enzyme, is a regulatory enzyme at the beginning of the pathway for the biosynthesis of pyrimidine nucleotides. ATCase exhibits positive cooperativity and is activated by ATP and inhibited by the pyrimidine nucleotide CTP. Both ATP and CTP affect the Km for the substrate aspartate but not Vmax when the second substrate (carbamoyl phosphate) is at saturation concentrations. List two important features of allosteric enzymes. What effect would a ratio of ATP:CTP of 1:4 have on the activity of ATCase? Draw a graph showing the activity of ATCase versus increasing aspartate concentration (draw the curve, no ATP or CTP present) and show a second curve that represents what you would expect with the ATP:CTP ratio of 1:4.
Sri K.
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