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I'm studying metabolic networks from a bioinformatics point of view, but I guess my question is pretty biological so I thought that maybe here I could get the best answers.

So, as the title says I was wondering, if I have one metabolite that is involved in two different reactions as reactant, is it possible that they both start at the same time at a certain point? I'm assuming that, in order to fire, the reactions need a certain amount of that metabolite, so if there is enough concentration to make both start, can the two reactions actually start in the same exact moment? What if the concentration of the metabolite is not enough to "satisfy" both?
Between the lines, are reactions mutually exclusive with respect to the shared metabolite or not?
In my mind, the quickest of the two gets the amount that it needs from the metabolite and the other one will just wait for the latter to have again enough concentration, is this intuition correct?

If you think this question is not appropriate, I will delete it and ask somewhere else. Any suggestion, also books or similar about the topic, is welcome!
I'm a computer scientist and I know just the basics of molecular biology, but I think that my job is mainly speaking to biologists in order to find solutions to different problems, so this is the reason why I chose to write here basically.

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    $\begingroup$ Are the two different competing reactions for the same metabolite enzyme-catalyzed? The kinetic parameters of the two enzymes as well as the levels of the enzymes, and whether or not the enzymes are inhibited by 'downstream' metabolic products ('feedback inhibition') might then be all-important. You might also want to check out the law of mass action. An example, though, of the type of competition you are thinking about would be great! $\endgroup$ – user1136 Aug 17 at 10:42
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    $\begingroup$ As a computer scientist, a little molecular biology is not going to help dispell your incorrect assumptions. You need to read some basic enzymology to find out how substrate concentration affects enzyme reactions and appreciate the stochastic nature of molecular interactions. Try section 8.4 of Berg et al. at NCBI Bookshelf. $\endgroup$ – David Aug 17 at 11:50
  • $\begingroup$ What do you mean by "moment"? How big is your time interval? Usually chemical reactions are modelled as Poisson process i.e. in an infinitesimally small time interval, the probability of happening of more than one events tends to be 0. Perhaps you should read about stochasticity in chemical reactions (check out papers by Dan Gillespie). When the amount of a reactant approaches such limits that you describe, the stochastic effects dominate. These reactions can be simulated using Monte-Carlo algorithms. However, your question does not directly concern biology and is hence off-topic. $\endgroup$ – WYSIWYG Aug 19 at 8:21

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