Lecture Notes: Photosystems in Photosynthesis

Overview of Thylakoid Structures

• Thylakoids contain:
  • ATP synthase
  • Electron transport chains
  • Photosystem I (PSI)
  • Photosystem II (PSII)

Photosystems Explained

General Structure of Photosystems

• Photosystems contain various pigments:
  • Photosynthetic pigments: Absorb light energy
  • Accessory pigments: Multiple types, each absorbing different wavelengths
    • Examples: Maroon, orange, purple (colors not to be memorized)
  • Reaction center: Two chlorophyll A molecules (Important)

Function of Pigments

• Accessory pigments: Absorb light at specific wavelengths
  • Example: Orange pigment absorbs 400 nm, purple pigment absorbs 700 nm
• Purpose: Maximize light absorption to range of 400-700 nm

Process of Light Absorption

1. Pigments absorb light energy
2. Energy is transferred to the reaction center
3. Reaction center becomes photoactivated
4. High-energy electron is released from the reaction center

• Purpose of electron release will be discussed later

Differences Between Photosystem I and II

• Photosystem I (PSI) and Photosystem II (PSII): Similar pigments and functions

Unique Feature of Photosystem II

• Contains an enzyme called Oxygen Evolving Complex (OEC)
  • Function of OEC to be discussed later

Important Additional Concepts

Electron Replacement in Reaction Center

• When a high-energy electron is released, it must be replaced to prevent destabilization of the reaction center
  • Replacement prevents breakdown and maintains stability
• Understanding this concept makes photosynthesis easier to explain