Overview
This lecture covers photosystems in photosynthesis, focusing on their structure, function, and the role of pigments in absorbing light energy.
Photosystem Structure
- Photosystems are complexes found in the thylakoid membrane involved in photosynthesis.
- Each photosystem contains multiple pigment molecules organized into accessory pigments and a reaction center.
- The reaction center of each photosystem contains two chlorophyll a molecules.
Types of Pigments
- Accessory pigments absorb light of various wavelengths and pass the energy to the reaction center.
- Different pigments maximize light absorption by capturing a spectrum of wavelengths (400–700 nm).
- The reaction center is the site where absorbed light energy is funneled and utilized.
Function of Photosystems
- Photosystems absorb light via pigments, transferring energy to the reaction center.
- Upon receiving enough energy, the reaction center becomes photoactivated and releases a high-energy electron.
- The primary role is to absorb light, activate the reaction center, and initiate electron release.
Photosystem I vs. Photosystem II
- Both photosystems have similar structure and function regarding light absorption and electron release.
- Photosystem II uniquely contains the oxygen-evolving complex enzyme, which participates in a later step.
Electron Replacement in the Reaction Center
- When the reaction center releases an electron, it must be replaced to maintain structural stability.
- Continuous loss of electrons without replacement would destabilize the reaction center.
Key Terms & Definitions
- Photosystem — Protein complex in thylakoids that absorbs light and releases electrons during photosynthesis.
- Accessory Pigments — Pigments that absorb different wavelengths of light and transfer energy to chlorophyll a.
- Reaction Center — The core of the photosystem, containing two chlorophyll a molecules, where photoactivation occurs.
- Photoactivation — Process where the reaction center absorbs enough energy to release a high-energy electron.
- Oxygen Evolving Complex — Enzyme present in photosystem II involved in water splitting (not detailed here).
Action Items / Next Steps
- Review the structure and function of photosystems, focusing on pigment roles and electron flow.
- Prepare for detailed study of the light-dependent reactions in upcoming lessons.