Chapter 22, Problem 15RE

Interpretation Introduction

Interpretation:

The reason for the requirement of a larger proton gradient in the chloroplast than in the mitochondria is to be determined.

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 chloroplast.

In the mitochondria, there is another type of gradient generation, called electrochemical gradient, which also contributes to the total potential energy production.