AAMC FL Practice Exam

What is an intermediate for the Calvin cycle derived from Ribose 5-phosphate?

1. Ribulose 5-phosphate

2. Fructose 1,6-bisphosphate

3. Glucose 6-phosphate

4. Erythrose 4-phosphate

The correct answer is: Ribulose 5-phosphate

Ribulose 5-phosphate is indeed an intermediate in the Calvin cycle that is derived from Ribose 5-phosphate. The pentose phosphate pathway, which is closely linked to the Calvin cycle, converts Ribose 5-phosphate into Ribulose 5-phosphate. This conversion is facilitated by the enzyme ribose-5-phosphate isomerase. In the context of the Calvin cycle, Ribulose 5-phosphate plays a crucial role, as it undergoes carboxylation with carbon dioxide to form 3-phosphoglycerate, which is then used to generate glucose and other carbohydrates. Understanding the relationship between Ribose 5-phosphate and Ribulose 5-phosphate is important, as it highlights how these compounds interact within metabolic pathways, particularly for photosynthetic organisms that rely on these processes for carbon fixation and energy production. The other options represent different metabolites that are not directly derived from Ribose 5-phosphate in the context of the Calvin cycle, thus making them less relevant to this specific question.