BIOL 204 Lecture Notes - Lecture 36: Light-Independent Reactions, Atp Synthase, Thylakoid
26 May 2018
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BIOL204 – Photosynthesis Stages
Photosynthesis Overview
- Amount of CO2 incorporated into organic form by photosynthetic organisms
= 11x1023 kg carbon/year
- Half of this is generated by marine photosynthetic microorganisms
phytoplankton
- Phytoplankton is found mainly near poles (Arctic) because water near
equator is warm but nutrient poor and cant support phytoplankton growth
- Photosynthetic organisms are:
o Photoautotrophs
o Primary producers
o Convert sunlight into chemical energy, assemble simple inorganic
molecules into complex organic ones
o They serve as food sources for consumers, and provide chemical
energy for bacteria/fungi/decomposers
2 Parts of Photosynthesis
- 2 Stages of photosynthesis (both happen in chloroplasts):
o 1) Light-dependent reactions (Light reactions)
▪ Capture light energy to synthesize NADPH and ATP
▪ ETC utilizes electrons donated from water, water is split and
oxygen is released as a by-product to environment
o 2) Light-independent reactions (Calvin cycle)
▪ Process of CO2 fixation - Electrons from NADPH and ATP are
used to convert CO2 from inorganic to organic
• Reduction where electrons are added to CO2,
converting it to a carbohydrate (1C:2H:1O)
▪ 3C sugars are the major product of Calvin cycle
- Overall equation of photosynthesis is: 6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O
- Sugar (glucose) is major product of photosynthesis
In Eukaryotes, Photosynthesis Takes Place in Chloroplasts
- Chloroplast is an organelle formed from 3 membranes that define 3
compartments:
o Outer membrane – covers surface of organelle
o Inner membrane – lies inside the outer membrane
o Intermembrane compartment – lies between outer/inner
o Stroma – aqueous environment within inner membrane, hold the 3rd
membrane, holds enzymes that catalyze the reactions of Calvin cycle
o Thylakoid membrane – third membrane, flattened closed sacs, holds
pigments, electron transfer carriers, ATP synthase enzymes
Electrons in Pigment Molecules Absorb Light Energy
- 3 fates of an excited-state electron within pigment:
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