A 43-year-old man prospecting for gold in Arizona becomes stuck in the desert after his truck breaks down. He brought a large supply of water with him but only a few granola bars as food. After 3 days, he is able to flag down a passing vehicle and obtain transportation to the nearest settlement. During this ordeal, his liver begins to synthesize large quantities of glucose from source molecules such as alanine, lactate, and glycerol. As part of this process, phosphoenolpyruvate is formed from oxaloacetate in a reaction that requires a specific nucleoside triphosphate as a cofactor. Which of the following reactions directly synthesizes this cofactor?

Question

A 43-year-old man prospecting for gold in Arizona becomes stuck in the desert after his truck breaks down.  He brought a large supply of water with him but only a few granola bars as food.  After 3 days, he is able to flag down a passing vehicle and obtain transportation to the nearest settlement.  During this ordeal, his liver begins to synthesize large quantities of glucose from source molecules such as alanine, lactate, and glycerol.  As part of this process, phosphoenolpyruvate is formed from oxaloacetate in a reaction that requires a specific nucleoside triphosphate as a cofactor.  Which of the following reactions directly synthesizes this cofactor?

Quizplus · Accepted Answer

11ec160b_36be_6019_9249_771086b90d56_MD0001_00 The majority of ATP used for cellular processes is generated by the oxidation of acetate in the tricarboxylic acid (TCA) cycle. The enzymes of the TCA cycle are located in the mitochondria and generate reduced nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FADH₂) (Choices C, D, F, and H). These molecules drive the process of oxidative phosphorylation, which converts their reducing potential into high-energy ATP via the electron transport chain. ATP can also be generated by substrate-level phosphorylation, which involves the direct transfer of a phosphate group from a reactive intermediate to a nucleotide diphosphate (eg, ADP, GDP). Succinyl-CoA synthetase converts succinyl-CoA to succinate and uses the high-energy thioester present in succinyl-CoA to drive GTP synthesis. This GTP can then be used to transphosphorylate ADP to ATP, or it may be utilized by specific GTP-hydrolyzing enzymes, such as phosphoenolpyruvate carboxykinase (converts oxaloacetate to phosphoenolpyruvate during gluconeogenesis). Educational objective: GTP is synthesized by succinyl-CoA synthetase during the conversion of succinyl-CoA to succinate in the citric acid cycle. During gluconeogenesis, phosphoenolpyruvate carboxykinase uses GTP to synthesize phosphoenolpyruvate from oxaloacetate.

A 43-Year-Old Man Prospecting for Gold in Arizona Becomes Stuck