Question

Both mitochondria and chloroplasts use electron transport to pump protons, creating an electrochemical proton gradient, which drives ATP synthesis. Are protons pumped across the same (analogous) membranes in the two oraganelles? Directionality of the pump? Is ATP synthesized in analogous compartments? Fully explain your answers.

Answer 1

Basic differences between Photophosphorylation & Oxidative phosphorylation:

S.No	Photophosphorylation	Oxidative phosphorylation
1	It is the process in which ADP is phosphorylated to ATP by using energy of sunlight	It is the process in which ATP is generated due to the transfer of electrons from NADH or FADH2 to oxygen.
2	Occurs during Photosynthesis	Occurs during Cellular Respiration
3	Takes place in chloroplast (Thylakoids)	Takes place in mitochondria
4	Used to make energy in the form of ATP	Used to make energy in the form of ATP
5	electrons are transferred through a series of membrane proteins	electrons are transferred through a series of membrane proteins
6	electrons provide energy to pump protons (H+) to one side of the membrane	electrons provide energy to pump protons (H+) to one side of the membrane
7	the protons flow back through a special enzyme (ATP-synthase) which makes ATP	the protons flow back through a special enzyme (ATP-synthase) which makes ATP
8	Energy source: Sunlight	Energy source: Glucose
9	Final electron acceptor: NADP+	Final electron acceptor: Molecular oxygen (O2)

Directionality of Proton pumping:

S.No	Photophosphorylation	Oxidative phosphorylation
1	chemiosmosis begins in the stroma (the fluid of the chloroplast)	chemiosmosis begins in the mitochondrial matrix
2	the protons are pumped into the thylakoids (the discs in the chloroplast) across the thylakoid membrane, before diffusing back out into the stroma	the protons are pumped out of the matrix (across the cristae) into the intermembrane space, before diffusing back into the matrix
3	ATP synthase are embedded into the thylakoid membrane	ATP synthase are embedded into the cristae
4	movement of protons during ATP synthesis – out of the thylakoid space in photosynthesis	movement of protons during ATP synthesis – into the mitochondrial matrix in oxidative phosphorylation