Are the phosphate groups of ATP protonated at pH = 7?

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In summary, ATP at a pH of 7 has four phosphate groups, each with one proton removed, making it quadruply deprotonated. This is similar to inorganic phosphate, which has a pK of 6.8 at neutral pH. In life, ATP is always complexed with magnesium and its fourth pK is estimated to be between 6.6 and 6.95. Magnesium is crucial for all reactions involving phosphate or pyrophosphate transfer.
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Homework Statement



The problem states: "Draw the chemical structure of ATP at a pH of 7.

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The Attempt at a Solution



The textbook diagrams the phophate groups as unprotonated, but since H3PO4 has a pKa of <7, I was thinking that maybe each phosphate group would have lost one hydrogen atom?
 
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You mean lost a hydrogen ion, i.e. a proton, so they are deprotonated as you say.
I think inorganic phosphate is a good guide: it is a strongish acid for the first dissociation (pK ca. 2) then the second dissociation is at near neutral pH's pK ca. 6.8.

In ATP correspondingly 3 protons are always lost at physiological pH's. The fourth pK I have seen given as various values 6.6 up to 6.95. So at intracellular pH of about 7 rather more than half should be quadruply deprotonated. Then in life it is all complexed with Mg2+ anyway. As far as I know there is not a single reaction involving phosphate or pyrophosphate transfer, which must be at least half of all important reactions, that occurs in the absence of magnesium.
 

1. What is the structure of ATP?

ATP, or adenosine triphosphate, is a nucleotide molecule that consists of a nitrogenous base (adenine), a sugar (ribose), and three phosphate groups.

2. What is the function of ATP in biological systems?

ATP serves as the primary source of energy for cellular processes in all living organisms.

3. How does the pH affect the protonation of the phosphate groups in ATP?

The pH of a solution can affect the protonation state of molecules, including the phosphate groups in ATP. At a pH of 7, the phosphate groups in ATP are not protonated, meaning they do not have a positive charge.

4. What is the significance of protonated phosphate groups in ATP?

The protonation of the phosphate groups in ATP can impact the stability and reactivity of the molecule, which can affect its function as an energy source.

5. How is ATP able to release energy during cellular processes?

When the third phosphate group in ATP is cleaved by a hydrolysis reaction, a large amount of energy is released, which can be used by cells to perform various functions.

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