1. 5.2 Light Dependent Reactions
Unit 5: Cell Energy
5.2 Light Dependent Reactions

2. Light Dependent Reactions
Two sets of chemical reactions that occur in the thylakoid membrane
Light-dependent reactions use energy from sunlight to:
Convert ADP into ATP
Convert NADP+ into the high energy carrier NADPH
Produce oxygen as waste

3. Photosystems
Photosystems: Clusters of proteins surrounded by accessory pigments in the membrane of the thylakoid (Similar structure to the cell membrane!)
Absorb sunlight and generate high-energy electrons that are passed to a series of proteins embedded in the thylakoid membrane

4. Chemical Reaction #1: Photosystem II
Light energy is absorbed
High energy electrons are produced and passed to the electron transport chain
Water molecules are split to replace those electrons
H+ ions and oxygen are released
ATP is synthesized

6. Electron Transport Chain
A series of proteins that shuttle electrons
Electrons move down the chain to photosystem I
Energy from electrons is used to pump H+ ions across the thylakoid membrane and into the thylakoid space to create a concentration gradient of H+ ions

7. Electron Transport Chain Analogy

8. Electron Transport Chain-ATP Synthesis
H+ then diffuse back into the cell across the enzyme ATP synthase.
This causes ATP synthase to rotate, creating energy.
ATP synthase captures the energy and uses it to create a bond between ADP and an additional phosphate.
This creates ATP!

10. Chemical Reaction #2: Photosystem I
The electrons have lost energy in the electron transport chain and need to be reenergized in photosystem I by absorbing more sunlight
A second electron transport chain transfers these electrons to produce NADPH

13. Animation