Re: What are excess amino acids? How does the body 'know' they are in excess?

Hi,

So a little googling reminded me that excess amino acids are broken into the carbon part for fuel or fat, while the nitrogen is made into urea. As you said.

Okay, so how are substances (amino acids, salt, calcium, molybdenum, etc) detected as being in excess - how does the body 'know'?

Simply put, I've no idea either - but I can give my best guess!

One idea might be that the body could be considered as one giant chemical reaction. I which case, it would follow Le Chatelier's principle. Which is really just a fancy way to say that if you put more of a substance in (increase the concentration) you get more of a substance out.

That assumes the body is a reaction at equilibrium. It most definately is not, as living systems are generally far from equilibrium (we manage to maintain our temperature despite changes in our surroundings). So that was probably not quite right. :)

Another idea then, is that the body is highly sensitive to change, and reacts to oppose it. Just as we maintain a nice warm ready-brek like glow inside by detecting changes in temperature and then shivering or metabolising fat or whatever; so can we detect increased levels of tyrosine, or salt, and take some metabolic action to resist this increase. Or decrease.

So, for example, in the short term an increase in an amino acid might cause pumps in cell membranes to be switched on to force the excess into the blood, and the subsequent rise in the blood might then activate transporters to take the excess into the liver, where the machinery (enzymes, that is) that converts amino acids into fats and urea switches up a gear...and so on.

In the long term, a prolonged increase in some metabolite (that is, some chemical) can trigger changes in gene expression, leading to more enzymes to break it down, or more pumps to pump it out, and so on. Of course, in a human, it might even lead the body to activate the mind somehow (to go to the doctor and say "my urine is a funny colour"...and then alter diet accordingly!).

So, sorry if this seems a bit like hand-waving (it is) but I didn't think that describing the detail of the metabolic pathways involved would be all that helpful. Hope that it's possible to communicate this now to the student. I guess I should say that organisms might well act like simple chemical reactions, in certain situations, but that there is this complex system of checks and balances on top to regulate and channel the basic chemical forces.

gilleain torrance