The Biology Project: Biochemistry

Photosynthesis Problem Set 1

Problem 2 Tutorial: Energy source for ATP formation

The specific energy source for the reaction ADP + phosphate ATP by the enzyme ATP synthetase (CF1 Coupling Factor) in thylakoid membranes is:

The role of a hydrogen gradient in ATP synthesis

During photosynthetic electron transport, protons accumulate at high concentration inside the thylakoid space. The concentration gradient between the inside and outside of the thylakoids is the energy source used by the ATP synthase. Protons pass through a channel of the CF0-CF1 ATP Synthase enzyme. This movement of protons from a region of high concentration (inner thylakoid space) to low concentration (stroma) activates the conversion of ADP and Pi to ATP.
In the Transmission Electron Micrograph (TEM) to the right, notice the ATP Synthase particles on the stromal surface of thylakoid membrane. Because the membranes are unstacked, the "sac-like" nature of the thylakoids is exaggerated in this photo. The interior of these sacs has a high proton concentration during electron transport.

The Biology Project
University of Arizona
Thursday, October 3, 1996
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