20. A practical class was going on where the students were demonstrating ATP synthesis in vitro using active mitochondria. Some students added one of the following to their tubes
A. Dinitrophenol (DNP), an uncoupler
B. Mild acidification of the medium
C. Glutilferone, that permeabilizes both the membranes
D. An outer membrane permeable He quencher compound. Elila
In which one of the above, ATP synthesis will be detected?
(1) A            (2) B
(3) C            (4) D

In practical classes demonstrating ATP synthesis in vitro using active mitochondria, various compounds can influence the ability of mitochondria to produce ATP. Understanding which conditions support or inhibit ATP synthesis is critical for interpreting experimental results.

The Compounds and Their Effects

• A. Dinitrophenol (DNP), an uncoupler:
  DNP dissipates the proton gradient across the mitochondrial inner membrane by shuttling protons back into the matrix, bypassing ATP synthase. This uncoupling of electron transport from ATP synthesis leads to increased oxygen consumption but no ATP production.

• B. Mild acidification of the medium:
  Mild acidification outside mitochondria increases the proton concentration in the intermembrane space, helping maintain or enhance the proton motive force. This supports ATP synthesis by ATP synthase, making this condition favorable for ATP production.

• C. Glutathione (likely intended as a membrane permeabilizer):
  If a compound permeabilizes both mitochondrial membranes, it disrupts the proton gradient and membrane potential, preventing ATP synthesis.

• D. An outer membrane permeable proton quencher compound (e.g., Elila):
  Proton quenchers collapse the proton gradient by neutralizing protons, uncoupling electron transport from ATP synthesis, thus inhibiting ATP production.

Why Mild Acidification Supports ATP Synthesis

• ATP synthesis depends on the proton motive force generated by a proton gradient across the inner mitochondrial membrane.

• Increasing proton concentration in the intermembrane space (acidification) enhances this gradient.

• This drives ATP synthase activity, resulting in ATP production.

Why Other Treatments Inhibit ATP Synthesis

• DNP (A) uncouples oxidative phosphorylation by collapsing the proton gradient.

• Membrane permeabilizers (C) disrupt membrane integrity, abolishing the proton gradient.

• Proton quenchers (D) neutralize the proton gradient, preventing ATP synthesis.

Summary Table

Final Answer:

(2) B — Mild acidification of the medium