Chapter 22, Problem 14RE

Interpretation Introduction

Interpretation:

The observation that uncouplers of oxidative phosphorylation in the mitochondria also uncouple the photoelectron transport and ATP synthesis in the chloroplast is to be explained.

Concept introduction:

There are a series of redox reactions that are coupled to the phosphorylation of ADP to ATP, which is called photophosphorylation.

${\text{ADP + P}}_{\text{i}}\to \text{ ATP}$

Photosynthesis occurs in the presence of light, and water is converted to oxygen by oxidation and ${\text{NADP}}^{\text{+}}$ is reduced to $\text{NADPH}$.

${\text{NADP}}^{\text{+}}{\text{ + H}}_{\text{2}}\text{O }\to {\text{ NADPH + H}}^{\text{+}}\text{ + }\frac{1}{2}{\text{O}}_{\text{2}}$

The $\text{NADH}$ are oxidized to ${\text{NAD}}^{\text{+}}$, while oxygen is reduced to water. The reaction is given as:

$\text{NADH + }\frac{1}{2}{\text{O}}_{\text{2}}{\text{ + H}}^{\text{+}}\to {\text{ NAD}}^{\text{+}}{\text{ + H}}_{\text{2}}\text{O }$

The coupling of the reaction depends on the proton gradient across the membrane in both the mitochondria and the chloroplast.