Photosynthesis: Electron Transport

Electron Transport in Photosynthesis

Overview

Electron transport is a critical stage in photosynthesis, generating ATP and NADPH for the Calvin cycle.

Components

• Electron transport chain: A series of protein complexes (electron carriers) in the thylakoid membrane that facilitate electron transfer.
• Plastocyanin: A copper-containing protein that plays a key role in electron transport.
• Cytochrome b6f complex: A protein complex that receives electrons from plastocyanin and passes them to photosystem I.
• Photosystem I (PSI): Receives electrons from the cytochrome b6f complex and generates a proton gradient.

Process

1. Light-dependent reactions: Light energy excites electrons in photosystem II (PSII), which are then transferred to the electron transport chain.
2. Electron transport: The electron transport chain passes electrons from PSII to PSI, generating a proton gradient across the thylakoid membrane.
3. Proton gradient: The gradient is used to produce ATP through chemiosmosis.
4. NADPH production: Electrons from PSI reduce NADP+ to NADPH, which is used in the Calvin cycle.

Significance

• Generates ATP and NADPH for the Calvin cycle
• Plays a crucial role in the light-dependent reactions of photosynthesis

Electron Transport in Photosynthesis

Overview

• Electron transport generates ATP and NADPH for the Calvin cycle in photosynthesis.

Components

• Electron transport chain: a series of protein complexes (electron carriers) in the thylakoid membrane that facilitate electron transfer.
• Plastocyanin: a copper-containing protein that plays a key role in electron transport.
• Cytochrome b6f complex: a protein complex that receives electrons from plastocyanin and passes them to photosystem I.
• Photosystem I (PSI): receives electrons from the cytochrome b6f complex and generates a proton gradient.

Process

• Light energy excites electrons in photosystem II (PSII), which are then transferred to the electron transport chain.
• The electron transport chain passes electrons from PSII to PSI, generating a proton gradient across the thylakoid membrane.
• The proton gradient is used to produce ATP through chemiosmosis.
• Electrons from PSI reduce NADP+ to NADPH, which is used in the Calvin cycle.

Significance

• Generates ATP and NADPH for the Calvin cycle.
• Plays a crucial role in the light-dependent reactions of photosynthesis.

Photosynthesis

Definition and Equation

• Photosynthesis: process by which plants, algae, and some bacteria convert light energy into chemical energy
• Overall Equation: 6 CO2 + 6 H2O + light energy → C6H12O6 (glucose) + 6 O2

Light-Dependent Reactions

• Occur in thylakoid membranes of chloroplasts
• Light energy excites electrons, which are used to generate ATP and NADPH
• Two stages:
  • Light absorption: light energy is absorbed by pigments (e.g., chlorophyll)
  • Electron transport: electrons are passed along a series of electron carriers, generating ATP and NADPH

Light-Independent Reactions (Calvin Cycle)

• Occur in stroma of chloroplasts
• ATP and NADPH from light-dependent reactions are used to convert CO2 into glucose
• Three stages:
  • Carbon fixation: CO2 is fixed into a 3-carbon molecule
  • Reduction: 3-carbon molecule is reduced to form glyceraldehyde 3-phosphate (G3P)
  • Regeneration: G3P is used to regenerate RuBP, the 5-carbon molecule that initiates the cycle

Importance of Photosynthesis

• Produces oxygen as a byproduct, essential for life on Earth
• Provides energy and organic compounds for the food chain
• Supports aquatic life through phytoplankton and aquatic plants