How to read biosynthetic pathways

[Axis8Mundi]

---

Members don't see this ad.

Here is a following question from TPR Bio workbook that pertains to the passage and diagram of the biosynthetic pathway I have attached.

The question reads:

What of the following are reactants in the production of purines?

A. Glutamine and PRPP only
B. Carbomyl phosphate and PRPP
C. glutamine and carbomyl phosphate
D. Gluatmine, CO2, ATP, and PRPP

The answer given is A and explains that glutamine and PRPP are the only building blocks while Answer D which includes CO2 and ATP are reactants.

My question is how do you read these diagrams. What qualifies as a reactant and what qualifies as a building block. Furthermore, doesn't the question ask for the 'reactants'?

 

[summergirl]

Lol, I remember this question from TPR Science workbook. It's A LOT easier if you just look at the diagram. They are asking about the reaction indicated by the diagonal arrow pointing to the bottom left corner , which makes GMP and AMP. You can see that the reactants are only glutamine and PRPP. If you want more confirmation, go to the passage and read the sentence about purines (right in the middle of your screenshot), which tells you the reactants.
CO2 and ATP are reactants for pyrimidines, as shown in the diagram.

 

[DocMC]

If there is a diagram that is the way to go. However I have noticed AAMC will explain heavy and dense pathways without diagrams. As soon as you realize you have this type of passage, start drawing it out as quickly as possible. It will save you a ****load of time on the questions that require an understanding of the pathway. The questions become much less intimidating. Goodluck.

 

[zporter301]

Yeah, I think like summergirl said, the question is asking you to know the difference between purines and pyrimidines.