 Previous |
Lecture index |  Next |
Lecture 28: Photosynthesis light reactions
Reading material: Principles of Biochemistry, Chapter 16.
Abstract: Photosynthetic organisms convert solar energy into chemical energy. In plants, algae, and cyanobacteria, complex carbohydrates are formed from water and carbon dioxide using light energy, but also anoxygenic organisms photosynthesise. In plants, photosynthesis takes place in the chloroplast. In the light reactions, water is split, oxygen gas is released, and NADPH and ATP is produced. In the Calvin cycle, (dark reactions) carbon dioxide is converted (fixed) to carbohydrate by using NADPH and ATP produced in the light reactions. The photochemical (light) reactions of photosynthesis take place in the thylakoid membrane of the chloroplast. Light is primarily absorbed by chlorophylls and carotenoids in light harvesting complexes and then rapidly transferred to a reaction centre where charge separation occurs. In plants, two reaction centres working in series, photosystem I and photosystem II creates sufficient reducing power to oxidise water, reduce NADP and generate a transmembrane proton gradient for ATP production. A transmembrane protein complex, the cytochrome b/f complex mediates the flow of electron from photosystem II to photosystem I and pumps protons into the tylakoid space. The protons flow back through an ATP-synthase in a way similar to mitochondrial ATP production. A cyclic electron flow through photosystem I leads to the production of ATP without concomitant production of NADPH.
Key concepts:
Chloroplast
Light reactions
Dark reactions
Thylakoid
Light harvesting complexes
Reaction centre
Photosystem I and II
Cytochrome b/f complex
ATP-synthase
Links:
Page created 98.01.05 by b6jamwoo@ulmo.stud.slu.se
Contents: Inger Andersson
Updated 2000.08.16 by stefan@xray.bmc.uu.se
Copyright © 1998-2000. Department of Molecular Biology SLU. All rights reserved.