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# Oxidative Phosphorylation and Photophosphorylation

BIOCHM-YYJ68F

Chloroplasts, like mitochondria, couple electron transport with the establishment of a proton gradient across a membrane and the synthesis of ${ATP}$ with a proton-translocating ${ATP}$ synthase complex.

Consider the 5 statements below comparing/contrasting chloroplast photophosphorylation with mitochondrial oxidative phosphorylation.

Select ALL of the statements that​ correctly describe BOTH processes.

A

In mitochondria, electrons are donated to the electron transport chain by reduced coenzymes (${NADH}$ and ${ FADH }_{ 2 }$) generated by oxidative metabolism.

In chloroplasts the source of electrons is sunlight.

B

In mitochondria, oxygen serves as the final electron acceptor producing water.

In chloroplasts the reverse occurs, water is split yielding oxygen, and the final electron acceptor is the coenzyme ${ NADP }^{ + }$.

C

In mitochondria, the electrochemical gradient driving ${ATP}$ synthesis is largely the voltage differential across the inner mitochondrial membrane (cristae).

In chloroplasts the electrochemical gradient driving force is largely generated by the difference in proton concentration or pH across the thylakoid membrane.

D

In animal mitochondria, electron transport and oxidative phosphorylation are independent of light.

In plants, mitochondrial oxidative phosphorylation only occurs in the dark and chloroplast photophosphorylation is strictly light dependent.

E

During electron transfer in mitochondria, protons are pumped into the intermembrane space and ${ATP}$ is synthesized in the matrix, but then transported out to the cytosol for anabolic metabolism.

In chloroplasts, electron transfer is coupled to the pumping of protons into the thylakoid lumen and ${ATP}$ is synthesized and used in the stroma in the carbon reduction cycle (Calvin cycle).