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Lectures 14 & 15: Photosynthsis (Two Sets of Reactions for…
Lectures 14 & 15: Photosynthsis
6CO2 + 6H2O = C6H12O6 + O2
CO2 Reduced, H2O oxidated
Two Sets of Reactions for Photosynthesis
Calvin Cycle (CO2 reduced to form carbohydrates)
Three Steps
Reduction
ATP Donates Phosphate, NAPDH reduces
Yields 3 Carbon Triose Phosphates
Regeneration
RuBP rebuilt from 5 Triose Phosphates
Carboxylation (Addition of CO2)
CO2 added to RuBP, catalyzed by Rubisco
Yields Six-carbon, then immediately Two Three-Carbon
Light-harvesting Reactions (ATP & NADPH generated to drive Calvin Cycle)
Proton Pump w/ help of plastoquinone
Cytochrome-b6 transports electrons from Photosystem II to Photosystem I
Pq, then Pc, then Fd transport electrons
NADP+ Reductase is final stop of electrons
Where does Photosynthesis take place?
In Eukaryotes, Calvin Cycle in Stroma, light-harvesting in thylakoid membrane
Photorespiration: When rubisco binds to oxygen instead of CO2. Reduces efficiency of photosynthesis
Chloroplast Anatomy
From outside to inside:
Intermembrane Space
Inner Membrane
Outer Membrane
Stroma (like cytoplasm of chloroplast)
Thylakoid membrane
Thylakoid Space
Antenna chlorophylls transfer light energy to reaction center (located in photosystems)
Protection from excess light energy: Antioxidants, Xanthophyll pigments
Photosystem II pulls electrons from water- Produces Oxygen & Protons inside thylakoid
Photosystem I reduces NADP+
Proton gradient in lumen drives production of ATP