Fall 2004 3rd Test Briefly explain what you would expect to be the most immediate effect on enzyme activity and cellular free energy change of the hexokinase-catalyzed reaction of glycolysis if the concentration of glucose-6-P was suddenly increased to 8.3mM from its usual steady-state concentration of 0.083mM. Hexokinase would slow down its activity of turning glucose into G6P. The cellular free energy would immediately decrease because the ATP being used to make G6P would no longer be needed Briefly explain why the hexokinase-catalyzed reaction, which is an irreversible step at the start of glycolysis, does not commit glucose to continue through glycolysis. Because at this point, glucose can still be used to foster another reaction. Whereas, if it were to the step with F-1,6-BiP, this can?t be used in other reactions, therefore, it has to go through with glycolysis. Cancer cells grow much more rapidly than do the blood vessels that nourish them; thus, as asolid tumors grow, they are unable to obtain oxygen efficiently to the point of experiencing hypoxia. How would you expect glycolysis in cancerous and normal cells to differ with respect to: Metabolic fate of pyruvate: Without Oxygen, the pyruvate would be unable to go through the TCA cycle, instead the pyruvate would form lactate Maintenance of redox via regeneration of NAD+ from NADH-H+: ___________________________________________________________________________________________________________________________________________________________________________________________________ ATP yield from catabolism of glucose: Since the pyruvate was unable to go through the TCA cycle rather than the 30-32 produced through the ATP cycle Briefly describe the four key reactions and mechanism of their regulation in the tricarboxylic acid cycle Briefly explain how bacteria are able to utilize acetate as their sole carbon source to achieve a net synthesis of tricarboxylic acid cycle intermediates, and eventually even sugar. Briefly explain why the malate-aspartate shuttle yields an average of 2.5 ATP whereas the glycerol-phosphate shuttle yields an average of only 1.5 ATP per mole of cytosolic NADH-H+ equivalent oxidized in mitochondrial electron transport. _ Briefly describe how metablic control of Glucose-6-phosphate utilization is achieved under cellular conditions where both NDAPH and ATP are needed, but ribose-5-phosphate is not. _ The most obvious symptom of diabetes is high blood glucose levels is caused by inadequate cellular uptake of glucose. In liver cells of a diabetic patient, glucose concentration is thus very low, and large amounts of acetyl-CoA are produced. Briefly describe how and by what metablic control mechanisms these symptons affect hepatic glycogen metabolism and glucogenesis in a diabetic patient. Briefly describe the mechanism by which steady-state intracellular [fructose-2,6-bis-phosphate] is regulated, and how fructose-2,6-bisphosphate in turn regulates the substrate cycle represented in the opposing pathways of glycolysis and gluconeogenesis. Briefly describe the process and purpose of cyclic electron transport in Photosystem I with respect to generation of O2, NADPH, and ATP. During normal metabolism, for example, the keto acid pyruvate can be easily converted to the amino acid alanine. Explain how this is possible, i.e., what is the biochemical mechanism for the conversion? When studying fatty acid oxidation and fatty acid synthesis of a saturated fatty acid, the first three steps/reactions in beta-oxidation (ignoring thiolase; step 4) and the last three steps/reactions in fatty acid synthesis in each synthesis cycle (ignoring thioesterase) are essentially the reverse of each other. Please explain this by contrasting and comparing these portions of oxidative and synthetic pathways for fatty acids. Start by listing the intermediates/metabolites and relevant enzymes in each of the two pathways. A hypothetical friend of yours (who is also a HUGE auburn football fan) has a daily energy requirement of about 1800 Kcal/day. Upon hearing that Auburn was shut out from the national championship game this person binged out on excessive amounts of carbohydrate-containing snack items, regular soft drinks and pizza. This Excess consumption will cause a consequent initiation of lipid anabolism. In the following list, enzymes found in liver or adipose involved with fatty acid synthesis and triacyglycerol synthesis from glucose are listed, but not in order, as follows: 1. Glycerol Phosphate acyl transferase 2. ATP citrate lyase 3. Pyruvate Dehydrogenase 4. AcetylCoA carboxylase 5. Diacylglycerol acyl transferase 6. Fatty acid synthase 7. Citrate synthase 8. All the glycolosis enzymes 9. Elongatses and desaturases Describe the biochemical function of: ATP citrate Lyase Ty Acid Synthase Glycerol Phosphate Acyltransferase When Amino acids or proteins are catabolized, the body will synthesize a nitrogen-containing excretory product Why is this so, and how does the handling of N differ rom catabolism of C- and H-containing metabolites? Outline the complete pathway of urea synthesis in liver cells (i.e. starting point, all intermediates, and enzymes, etc.) Draw the chemical structure of urea and indicate what the origins of the two nitrogen atoms are in the urea molecule
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