A student is trying to determine the mechanism for a reaction that uses ATP to a
ID: 1000889 • Letter: A
Question
A student is trying to determine the mechanism for a reaction that uses ATP to activate a carboxylate ion, which then reacts with a thiol. If the carboxylate ion attacks the -phosphorus of ATP, the reaction products are the thioester, ADP, and phosphate. However, whether it attacks the -phosphorus or the -phosphorus of ATP cannot be determined from the reaction products because the thioester, AMP, and pyrophosphate would be the products in both reactions. The mechanisms can be distinguished by a labeling experiment in which the enzyme, the carboxylate ion, ATP, and radioactively labeled pyrophosphate are incubated, and ATP is isolated. If the isolated ATP is radioactive, attack occurred on the -phosphorus. If it is not radioactive, then attack occurred on the -phosphorus. Choose an explanation out of A, B, C, D.
A) ATP will become radioactive if the mechanism involves attack on the -phosphorus because pyrophosphate is a reactant in the reverse reaction that forms ADP. ATP will not become radioactive if the mechanism involves attack on the -phosphorus because pyrophosphate is not a reactant in the reverse reaction that forms ADP.
C) ATP will become radioactive if the mechanism involves attack on the -phosphorus because pyrophosphate is a product of the reverse reaction that forms ATP. ATP will not become radioactive if the mechanism involves attack on the -phosphorus because pyrophosphate is not a product of the reverse reaction that forms ATP.
D) ATP will become radioactive if the mechanism involves attack on the -phosphorus because pyrophosphate is a reactant in the reverse reaction that forms ATP. ATP will not become radioactive if the mechanism involves attack on the -phosphorus because pyrophosphate is not a reactant in the reverse reaction that forms ATP.
A) ATP will become radioactive if the mechanism involves attack on the -phosphorus because pyrophosphate is a reactant in the reverse reaction that forms ADP. ATP will not become radioactive if the mechanism involves attack on the -phosphorus because pyrophosphate is not a reactant in the reverse reaction that forms ADP.
B) ATP will become radioactive if the mechanism involves attack on the -phosphorus because phosphate is a reactant in the reverse reaction that forms ATP. ATP will not become radioactive if the mechanism involves attack on the -phosphorus because phosphate is not a reactant in the reverse reaction that forms ATP.Explanation / Answer
D) ATP will become radioactive if the mechanism involves attack on the alpha-phosphorous because pyrophosphate is a reactant in the reverse reaction that forms ATP.
ATP will not become radioactive if the mechanism involves attack on beta-phosphorous because pyrophosphate is not a reactant in the reverse reaction that forms ATP.
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