Flux and demand reactions

[kmerfeld]

Hello,

 

I am a beginner in this area. My background is in mathematics but was just hired to work in a biochemistry lab on campus, doing genome reconstruction and modeling. So I'm trying to get up to speed on some biochemistry terms.

 

The first one is flux. Here's my understanding: flux is essentially the amount of a subtance "passing through a certain volume." Is that essentially what it is? The amount of moles moving through a given space?

 

The second is demand reactions. My understanding is that these are reactions that consume metabolites but do not produce anything. That seems like an impossible reaction but that's how it was described to me. Can someone enlighten me on how these reactions work?

Thanks a lot,

 

Kevin

[BabcockHall]

I have never heard of demand reactions. Flux is sometimes used in metabolic control analysis, and for a pathway operating under steady state conditions, the overall flux through the pathway is equal to the rate of each step. Rates are typically given in units of concentration over time. I could also see flux being used as you suggest, but I have not encountered it myself.

[CaptainPanic]

Hello,

 

I am a beginner in this area. My background is in mathematics but was just hired to work in a biochemistry lab on campus, doing genome reconstruction and modeling. So I'm trying to get up to speed on some biochemistry terms.

 

The first one is flux. Here's my understanding: flux is essentially the amount of a subtance "passing through a certain volume." Is that essentially what it is? The amount of moles moving through a given space?

 

No, it is through an area... like through a window.

The material is passing through an area, to get into a volume. (And it might eventually also leave that volume again, but that is irrelevant).

 

The second is demand reactions. My understanding is that these are reactions that consume metabolites but do not produce anything. That seems like an impossible reaction but that's how it was described to me. Can someone enlighten me on how these reactions work?

 

Thanks a lot,

 

Kevin

 

I am not familiar with the term (but them I am a chemical engineer, not 100% expert in this field).

It could be "maintenance reactions". Maintenance is essentially a microorganism eating food, but not growing and not producing any product either. It's just maintaining its own body. It fits your description of no production... but I have never heard the word "demand" used in this context.

 

It could also have something to do with electron donors and electron acceptors... at least then the word "demand" would make more sense, but it doesn't really seem to fit the rest of the description.

 

Hope these two remarks can somehow put you on the right path. Also, there's a fair chance someone else will pass by this thread to enlighten you

[CharonY]

In metabolic contexts flux is not referring to volumes in a spatial sense, but are usually used to describe biochemical reactions. A compartment could then essentially be a metabolite pool and the flux would be defined by the reactions to and from that pool.As BabckockHall mentioned, often steady-state conditions are assumed, though it does not have to be the case (really depends on your modeling for instnframework).

Demand reactions, for instance, are simply unbalanced network reactions that allow compound accumulation. Under steady-state assumption the influx should equal the outflux. In reality, certain compounds may accumulate and this often has to be fit in into a given model somehow.

 

You may want to get some reads on biochemical systems theory (which is a bit oldish term but still pretty much the basis of it all) or books about metabolic modeling.

Edited March 13, 2013 by CharonY

[kmerfeld]

Thanks for your responses. I think I have the jist of it now.