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What neutralizes important ions in the cell?

by Erland
Tags: cell, important, ions, neutralizes
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Erland
#19
Jul14-14, 06:43 AM
P: 339
It was perhaps unwise of me to use word "neutralize", since that indicates some kind of action by some kind of agent. Some of you seem to believe that I meant something like that. I didn't.

What I mean is simply this: If the typical net charge of a cell is at most 15 millions units of elementary charge (positive or negtive) and if there is a billion ATP-molecules in the cell, each with a net charge of -4 units of elementary charge, then there must be other particles/ions in the cell with a total charge of at least +3.985 billions units of elementary charge. This is simply a logical consequence of the assumptions (based on the article Simon linked to). So I just wonder which these positively charged particles/ions are.

It could of course be that NAD+ balances a substantial part the ATP but to me, this does not seem very plausible, since this seems to indicate some kind of connection between ATP and and NAD+ which I am unaware of.

Sodium and magnesium ions have also been suggested in the thread, and this seems more plausible to me. After all, the phosphorus in ATP must ulimately come from food (unless it is present in very large amount at birth and then becomes diluted as we grow, but this does not seem plausible), and phosporus in the food might come from salts such as sodium phosphate and magnesium phosphate.
My own guess, that the "counterions" (good word, never heard it before) are mainly hydrogen, is less likely. I thought it came from phosphorus acid, but I don't think we ingest so much of that (again, correct me if I am wrong).

I will look at the links you people gave more closely, but I now consider the question of the counterions to ATP as anwered. Thanks for that, all!

So, now remains the question of the counterions in the cell to NAD+...
atyy
#20
Jul14-14, 09:36 AM
Sci Advisor
P: 8,395
Quote Quote by Simon Bridge View Post
... well in blood, the sodium is typically outside the cell, hence the membrane potential.
But sure - if that is the question, then Na+ would be a reasonable answer, though, considering the reasoning, I'm concerned it is misleading...

How about it Eriand, is that what you wanted to know?
Quote Quote by Erland View Post
It was perhaps unwise of me to use word "neutralize", since that indicates some kind of action by some kind of agent. Some of you seem to believe that I meant something like that. I didn't.

What I mean is simply this: If the typical net charge of a cell is at most 15 millions units of elementary charge (positive or negtive) and if there is a billion ATP-molecules in the cell, each with a net charge of -4 units of elementary charge, then there must be other particles/ions in the cell with a total charge of at least +3.985 billions units of elementary charge. This is simply a logical consequence of the assumptions (based on the article Simon linked to). So I just wonder which these positively charged particles/ions are.

It could of course be that NAD+ balances a substantial part the ATP but to me, this does not seem very plausible, since this seems to indicate some kind of connection between ATP and and NAD+ which I am unaware of.
@Simon Bridge, I think Erland's understanding is similar to yours? It doesn't seem he's asking for so specific a counterion, just for example, whether it is sodium, magnesium, hydrogen etc.

Quote Quote by Erland View Post
Sodium and magnesium ions have also been suggested in the thread, and this seems more plausible to me. After all, the phosphorus in ATP must ulimately come from food (unless it is present in very large amount at birth and then becomes diluted as we grow, but this does not seem plausible), and phosporus in the food might come from salts such as sodium phosphate and magnesium phosphate.
My own guess, that the "counterions" (good word, never heard it before) are mainly hydrogen, is less likely. I thought it came from phosphorus acid, but I don't think we ingest so much of that (again, correct me if I am wrong).

I will look at the links you people gave more closely, but I now consider the question of the counterions to ATP as anwered. Thanks for that, all!

So, now remains the question of the counterions in the cell to NAD+...
@Erlang, I wouldn't take my suggestions as anything close to final. I thought your question was reasonable, and was just trying to explain it (maybe) a bit to Simon Bridge. To be honest, I had guessed hydrogen too. I don't understand the sodium answer - sodium is high in the extracellular fluid, but is that also the case in the cell?
Ygggdrasil
#21
Jul14-14, 11:09 AM
Other Sci
Sci Advisor
P: 1,379
1) Let's say you have water and you mix in some sodium chloride and sodium acetate. In the solution, what ions are neutralizing the sodium? The sodium ions exist surrounded by a solvation shell of water, and do not interact with either the chloride or acetate ions in solution. Basically all of the negative charges in the water (the chloride and acetate ions) are helping to neutralize the charge of the sodium ions. So, when you ask what ions in the cell neutralize the charge of the ATP, the answer is all of the positively charged substances in the cell.

2) Now, we've reduced the question to one with a much clearer answer: what are the main charged ions present in the cell? The following wikipedia page is probably relevant for this discussion: http://en.wikipedia.org/wiki/Cytosol#Ions

Potassium is the primary cation present inside cells. Most of the negative charge inside of cells is probably accounted for by the proteins (which tend to have an overall negative charge) and DNA. Calcium and magnesium are important cations within the cell (and regulate many important proteins), but these cations are often bound by proteins and thus the free concentrations are quite low.
atyy
#22
Jul14-14, 02:53 PM
Sci Advisor
P: 8,395
@Ygggdrasil, would the answer be different depending on whether the ATP is in the cytosol or a mitochondrion, or is potassium also the major cation in mitochondria?

Also, how about the magnesium which googling about seems to indicate is coordinated with ATP, at least in the cytosol? Does that mean that magnesium is associated with ATP more closely than the ratio of free magnesium to potassium ions would suggest?
Ygggdrasil
#23
Jul14-14, 10:02 PM
Other Sci
Sci Advisor
P: 1,379
I'm not aware of any mechanisms that would cause potassium to not be the major cation in mitochondria, but a quick search didn't yield any good sources describing the concentrations of ions in the mitochondrial matrix.

I have also heard that magnesium ions are coordinated by the triphosphate group of nucleotides (and this would make some sense because most enzymes that use nucleotide triphosphates require magnesium as a cofactor), but this is probably a special case.


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