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Objectives
- Describe the components in the cell necessary to carry out the light reactions
- Explain the process of how light energy results in the formation of NADPH and ATP
- Discuss the flow of electrons from PSII to PSI
Key points
- The structure of chlorophyll allows it to absorb light in the blue and red parts of the spectrum
- chlorophyll is not free-floating in the chloroplast, but rather is bound to membrane proteins in the thylakoid
- the long fatty-acid chain on chlorophyll allows it to associate with the hydrophobic regions of these proteins
- Photochemistry (the removal of an electron from chlorophyll) only occurs at photosynthetic reaction centers
- reaction centers are surrounded by light harvesting complex proteins that act as antennas to harvest light
- transfer of energy between light-harvesting complex chlorophylls and reaction center chlorophylls is by resonance energy transfer
- Electron flow through the reaction center creates a H+ gradient
- flow is linear, with electrons re-supplied by the hydrolysis of H2O and reducing NADP+ to NADPH
- the H+ gradient drives the formation of ATP from ADP and Pi
- the energy for this electron flow comes, ultimately, from light
Questions for Practice
- Compare and contrast the electron transport system of photosynthesis with that of respiration. Identify the electron donors, transporters, membranes, H+ gradient, and terminal electron acceptor.
- Describe or draw the photosynthetic electron transport system.
- What role do the light harvesting complex proteins play in the light reactions?