Question

Use the data in Table2-4to estimate the net charge of an ATP molecule in vivo.

Short answer

In vivo, ATP has a net charge between to -3.5 to -4 .

Step-by-step solution

ATP Molecule

The organic complex adenosine triphosphate powers a variety of biological functions in living cells, including muscular contraction, nerve impulse transmission, and chemical synthesis.

Estimation of the net charge of an ATP molecule

The three phosphate groups in ATP behave similarly to the phosphate groups in phosphoric acid.The following are the $\text{pKa}$ values for phosphoric acid obtained from the table 2-4 :

$$\begin{gathered} {\text{pKa}}_{\text{1}}\text{= 2.15,} \\ {\text{pKa}}_{\text{2}}\text{= 6.82,} \\ {\text{pKa}}_{\text{3}}\text{= 12.38} \end{gathered}$$

Since each phosphoryl group has a pK value of 2.15, ionisation of the first proton on each one is complete at physiological pH (7.4), while ionisation of the second proton, if present, is more than halfway complete (since pH 7.4 is greater than the pK value of 6.82). Consequently, an ATP molecule has a net charge of between 3.5 and 4.

Hence, the net charge of ATP is between -3.5 and -4 .