Of the following statements about metabolic pathways is correct? So for A, it says the product of the last reaction in a cyclic metabolic pathway is a reactant in the first reaction. This is true. Remember, when we looked at the cyclic pathway, we ended with our product D. But product D can feed back into our first reactant A and the cycle begins all over again. So, basically the product of a reaction can help to become, the substrate or reactant of the next reaction. So here, A is true.
Catabolism always takes place through cyclic pathways. That is not true. Catabolism could go through linear or cyclic pathways. We talked about both possibilities when it comes to metabolism.
Linear catabolic pathways produce energy while cyclic catabolic pathways use energy. We never said this. All we said is that there are two types of pathways. There are linear as well as cyclic. We never talked about either of them creating energy or using energy.
And then here, the last reaction in some linear pathways can produce a starting material for the first reaction. Now in a linear reaction, think of it as a chain of reactions connected together, interconnected together, and it's an assembly line. At the end of the assembly line, that's it. That's our last product. That product doesn't loop back around to make our beginning reactant. So here, option A would be the only correct statement.
