Turning glutamate into ribose-5-phosphate

[NicolasL]

Homework Statement

The question is simple: how much moles of ribose-5-P can you make from glutamate?

The Attempt at a Solution

I first turned glutamate into alpha ketoglutarate. I then put it in the Krebs cycle turning it into oxaloacetate. I then used the anaplerotic reactions to turn it into pyruvate. The pyruvate is transformed through neoglucogenesis to 2 fructose-6-P and glyceraldehyde-3-P (I think I need 5 pyruvates for this). I then put them into the pentose phosphate pathway which gives me 1 mole of ribose-5-P, but the answer should be 3 moles. Any help ?

 

[nate808]

Your approach is correct, but there are a few things to consider. First, you mentioned using 5 pyruvates for neoglucogenesis, but this only yields 1 fructose-6-P and 1 glyceraldehyde-3-P. So you would need a total of 10 pyruvates to get 2 fructose-6-P and 2 glyceraldehyde-3-P for the pentose phosphate pathway.

Second, the pentose phosphate pathway can also produce NADPH in addition to ribose-5-P. So for every 1 mole of ribose-5-P, you would also produce 2 moles of NADPH. This means that for 3 moles of ribose-5-P, you would need a total of 6 moles of NADPH.

Lastly, the pentose phosphate pathway can also produce other sugars such as glucose-6-P and erythrose-4-P, which can then be converted to ribose-5-P. So you may need to consider these other pathways as well in your calculation.

Overall, it is difficult to give an exact answer without knowing the specific conditions and enzymes involved in the process. But with these considerations in mind, you should be able to adjust your calculation to get a more accurate answer.