Photosynthesis Lecture Notes

Overview

Photosynthesis is essential for life as it converts sunlight, CO2, and water into glucose and oxygen.
Developed 450 million years ago.
Comprised of two main types of reactions:
- Light-dependent reactions
- Light-independent reactions (Calvin Cycle)

Chloroplasts: Key organelle containing chlorophyll.
- Thylakoids: Membranous sacs where chlorophyll is stored.
- Grana: Stacks of thylakoids.
- Stroma: Space surrounding thylakoids.
- Thylakoid membranes: Phospholipid bilayers maintaining ion concentration.

Initiation by photons exciting chlorophyll electrons.
Photosystem II (PSII):
- Electron Transport Chain: Transfers excited electrons, capturing energy.
- Involves water splitting to replenish lost electrons, releasing oxygen.
Cytochrome Complex:
- Transfers electrons from PSII to Photosystem I (PSI).
- Pumps protons into thylakoid, creating a concentration gradient.
ATP Synthase:
- Uses proton gradient to convert ADP to ATP.
Photosystem I (PSI):
- Re-excites electrons to help form NADPH.
End products: ATP, NADPH, and oxygen.

Occurs in the stroma.
Carbon Fixation:
- CO2 combines with Ribulose Bisphosphate (RuBP) using the enzyme RuBisCo.
Reduction Phase:
- ATP and NADPH convert 3-Phosphoglycerate to G3P.
- G3P can form carbohydrates like glucose.
Regeneration of RuBP:
- Requires 5 G3Ps to regenerate 3 RuBPs.
- Consumes ATP and NADPH.
Cycle results in formation of G3P: used for carbohydrate synthesis.

RuBisCo's role in CO2 fixation and inefficiency due to presence of oxygen in the atmosphere.
Importance of understanding the enzyme functions and cycles for exams.
Encouragement to review materials for better understanding.