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Photosynthesis Notes

Pharmacology Notes > BIOL10212 Biochemistry Notes

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Lecture 19/20 - Biochemistry - 23-26/04/18
INTRODICTION TO PHOTOSYNTHESIS:A process that converts light energy into chemical energy. This chemical energy is used to convert atmospheric CO2 into carbohydrate
Solar energy is captured and converted into chemical potential as ATP and
ATP and NADPH are then used to convert CO2 to sugar phosphates (and then to carbohydrates)Several autotroph organisms are able to capture electromagnetic radiation from the visible spectrum (380-700 nm) of the Sun and convert it into chemical energy
à Green plants (40% of conversion)
à Algae and bacteria (60% of conversion)
Net reaction of photosynthesis can be represented as:
6CO2 + 6H2O + energy (light) → C6H12O6 + 6O2
Reverses oxidation of glucose through cellular respiration to produce energy:
C6H12O2 + 6O2 → 6CO2 + 6H2O + energy (ATP)

6CO2 + 6H2O + energy (light) → C6H12O6 + 6O2-

The oxidation of water is driven by solar energy during the light reactions of photosynthesis
Electrons from water oxidation pass through an electron-transport chain (which resembles the mitochondrial Electron Transport Chain) to NADPH and create a proton gradient
Proton gradient is used to synthesize ATP

THE 'DARK PHASE' OF PHOTOSYNTHESIS:"Dark phase" reactions are light-independent, carbon-fixation reactions
Reduction of gaseous CO2 to carbohydrate
Requires reducing power and energy which is provided by NADPH and ATP LIGHT-DEPENDENT REACTIONS OF PHOTOSYNTHESIS:High energy electrons are transported through two photosystems, reducing power is generated, then ATP is synthesized.Electrons derived from H2O oxidation drive the formation of a proton gradient which is then used in the synthesis of ATP
Electrons derived from H2O oxidation eventually reduce NADP+ to NADPH
O2 is a by-product of water oxidation

2H2O + 2NADP + 3Pi + 3ADP ⇄ 2NADPH + 2H + O2 + 3ATP


CHLOROPLAST STRUCTURE:Thylakoids contain flattened sacks which contain chlorophyll and the other components required for light phase of photosynthesis PHOTOPHOSPHORYLATION OVERVIEW:

1. Chlorophyll-containing structures are photosystem I
and photosystem II

2. Cytochrome bf links PSII
and PSI. Plastoquinone,
plastocyanin, ferredoxin are the electron carriers

3. ATP-synthase uses high concentration of protons in thylakoid lumen as source of energy → ATP synthesis

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