[El_Duderino]

Ok, so I listed the problems below that I have been having an issue with. Is the work that I have done on #'s 5, 6, and 7 correct? If so, how do I approach #8? I am having difficulty relating the % dissociation to the mitochondria and cytosol, as there's nothing about it in our notes.


5. The pH in the mitochondrion is 8.4 while the pH in the cytosol is 7.4. What is the difference in hydrogen ion concentration between the cytosol and the mitochondria?

pH = -log[H+]

8.4-7.4 = -log[H+]
1 = -log[H+]
 -1 = log[H+]

Difference in [H+] = 0.1 M


6. 2,4-Dinitrophenol has a pKa of 4.1. What fraction of the 2,4-dinitrophenol in the cytosol (pH = 7.4) is available for diffusion into the mitochondria?

Difference between pH and pKa is great (3.3), so:

100% Disocciated into mitochondria


7. What fraction of the 2,4DNP (pKa = 4.1) is available to move from the mitochondria (pH = 8.4) to the cytosol?

0%


8.      Based on the previous three questions, explain why 2,4DNP becomes trapped within mitochondria?

[renge ishyo]

What does a mitochondrion have as a general feature that largely prevents charged particles from exiting it? Think about the structure of the mitochondrion.

[El_Duderino]

What does a mitochondrion have as a general feature that largely prevents charged particles from exiting it? Think about the structure of the mitochondrion.

Selective outer membrane?

Also, was I correct in #'s 5-7?

[renge ishyo]

The selective outer membrane explains why the negatively charged base version of DNP can't cross the membrane, the neutral acidic version still can. The answer for #8 wants you to base the logic on the calculations made for questions #6-7.
For question #'s 6 and 7 actually calculate it out using the Hendersen Hasselbach equation to get the amount of base to acid both inside and outside. Compare the two ratios with the knowledge that only the acid version can cross the membrane while the base cannot.

For question 5, first convert to the hydrogen ion concentration at pH 8.4 and then again at pH 7.4 before subtracting the two numbers. Note that the pH concentration of 7.4 corresponds to a higher hydrogen ion concentration.

Hope this helps.