LSM1401 Semester 2 2007‐08
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Tutorial 3
(24, 25, and 26 March 2008)
Questions
1. Pyruvate labelled with 14C in the methyl carbon was administered to isolated liver cells.
(a) Draw the structure of isocitrate, indicating the carbon(s) labelled with 14C, which would be produced after the first turn of the citric acid cycle.
(b) Malonate is a competitive inhibitor of succinate dehydrogenase, the enzyme that catalyses the dehydrogenation of succinate to fumarate. The isolated liver cells were treated with sufficient malonate to ensure that the activity of succinate dehydrogenase was completely inhibited and then administered with pyruvate labelled with 14C in the methyl carbon. After a time, isocitrate with the following structure was isolated.
Explain the observation.
2. Using the P/O ratios of 2.5 and 1.5 for the mitochondrial oxidation of NADH and FADH2 respectively, calculate the net ATP yield from the complete oxidation of
(a) 1 mole of oleic acid, 18:1(Δ9), and
(b) 1 mole of linoleic acid, 18:2(Δ9,12). Assume that the ATP yields of NADPH and NADH are the same.
3. In the presence of inorganic phosphate, fluoride ions inhibit the activity of enolase, the enzyme that catalyses the dehydration of 2‐phosphoglycerate to phosphoenolpyruvate. It has been observed that besides 2‐phosphoglycerate, 3‐phosphoglycerate also accumulates in the presence of inorganic phosphate and fluoride ions. However, 1,3‐bisphosphoglycerate does not accumulate. Explain.
LSM1401 Semester 2 2007‐08
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4. An adult uses about 7000 kJ of free energy daily. If the molecular weight of ATP is 507 and the ΔG°' for the synthesis of ATP from ADP and Pi is +30.5 kJ/mol, under standard biochemical conditions, calculate
(a) how many moles of ATP must be hydrolysed daily to provide the required amount of free energy,
(b) the mass of the total ATP hydrolysed daily, and
(c) how many times a molecule of ADP must be recycled daily if the total amount of ATP in an adult is 0.1 mole.
5. Consider to the following structure of palmitic acid.
Calculate the net ATP yield when one molecule of palmitic acid
(a) is completely oxidised to CO2 and water, and
(b) is converted to acetacetate in the liver, transported to the heart and oxidised to CO2 and water. The conversion of acetoacetate to acetyl‐CoA in the heart requires succinyl‐ CoA as donor of CoA.
Use the P/O ratios of 2.5 and 1.5 for the mitochondrial oxidation of NADH and FADH2 respectively in your calculations.
6. IVLE Review Questions on topics of (a) “Lipid Structure and Function”,
(b) “Carbohydrate Structure and Function”, and (c) “Cellular Metabolism”.
