Pigments
Molecules with great ability to absorb photons
Eg) chlorophyll, indigo, retinal
What does it mean by absorbing light
Occurs when the person energy of the photon is transferred to an electron within a molecule
What is photosynthesis
Use of light energy to convert co2 into organic compounds such as carbohydrates
Water in photosynthesis
Oxidized to 02( loses electrons)
Co2 in photosynthesis
Reduced to glucose( gains electrons)
Photosynthetic apparatus
Series of large protein complexes embedded in the thylakoid membrane that are responsible for light reactions
Chlorophylls
Major photosynthetic pigments in plants, green algae, and Cyanobacteria
- contains both a and b molecules
Photosystem 1
Absorbs at 700nm wavelength
- P700
- occurs second in membrane
Photosystem 2
Absorbs light at 680nm wavelength
- P680
- occurs first
What is a Photosystem
Complexes by which pigments are bound very specifically to proteins. These pigment proteins are organized in the thylakoid membrane in complexes called photosystems.
Linear Electron Flow
1) PS2 transfers electron to primary electron acceptor. PS2 is oxidized and now needs and electron; rips electrons from H2O, protons are released in thylakoid
2) excited electrons move from PEA to the ETC
- energy is used to power proton pumps
3) electrons move through PQ, cytochrome complex, PC to PS1
- moves excited electron to primary electron acceptor; PS1 needs an electron
4) electron moves through ferredoxin to NADP+ reductase to reduce NADP+ into NADPH
What is the final electron acceptor in linear electron flow
NADPH
How does the first Photosystem get its electron filled
From the ETC before it
Cyclic Electron Flow
Makes more ATP than NADPH
- only uses PS1( P700)
1) electrons in P700 are excited and transferred to PS1 primary electron acceptor
2) High energy electrons move to ferredoxin
3) electrons move backwards to the cytochrome complex
- pumps protons and ATP is produced by chemiosmosis
4) electrons move to PC then back to P700 to fill the electron hole lol
Where do light dependent reactions take place
The thylakoid membrane
Where do light independent reactions take place
Occurs in the stroma
- synthesises sugars using energy from light reactions
Phase 1 of fixation.
Fixing a carbon atom into one molecule of the 5 carbon sugar RuBP to produce 2 molecules of 3 carbon compound 3- phosphoglycerate
Phase 2- reduction
Each molecule of 3-phospholycerate gets additional phosphate due to breakdown of ATP
- produce 2 molecules of 1,3- biphosphoglycerate. Each is gen reduced by electron from NADPH producing G3P
Phase 3- Regeneration
- each turn of Calvin cycle producing 2 molecules of G3P
- in multi step process, 5 of 6 carbons are re arranged to regenerate the single molecule of RUBP required for next round of carbon fixation
Chemiosmosis
Use of the proton gradient to drive the synthesis of ATP
- built over thylakoid membrane by linear electron flow
Calvin cycle process simplified
Ribulose Bisphosphate Carboxylase- Oxygenase fixes C02 to form 3-phosphoglycerate
3- phosphoglycerate gets reduced from 6ATP+6 NADPH into G3P
5 G3P and 3ATP regenerates 3 RuBP which is used in the next cycle to fix three more CO2
What is G3P used for
Used in cytosol to build
- sugars such as glucose
- fuel for cellular respiration
- building blocks for other molecules
