Q: About Metabolic Cycles


Glyoxylate Cycle

Glyoxylate Cycle


(I-07) A metabolic cycle can be defined as a metabolic pathway in which one of the final products is at the same time, one of the initial metabolites of the pathway, e.g. one initial metabolite is regenerated through the reactions of the metabolic pathway.  Observe the following metabolites. All of them have in common that they participate in metabolic cycles.


a)     acetyl CoA

b)     arginine

c)      alpha-ketoglutarate

d)     citrate

e)     citruline

f)       fumarate

g)     isocitrate

h)    malate

i)       ornithine

j)       oxalacetate

k)     succinate

l)       succinyl CoA

m)  urea



For each of the following metabolic cycles, which of the metabolites that appears above is the one that initiates and “close” the metabolic pathway, and so, allow us  to consider the pathway as a cycle?


1.- For the Krebs Cycle




2.- For the Urea cycle






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