Photosynthesis Flashcards
What is the equation for photosynthesis?
CO2 + H2O –(light)—> (CH2O) + O2
What are the 2 stage processes in photosynthesis?
2H2O —(light)—-> O2 + 4[H*]
4[H*] + CO2 —–> (CH2O) + 4H2O
Where does photosynthesis occur?
The chloroplast
What are the 6 key points about a chloroplast?
- 5um long
- 1 to 1000 per cell
- Impermeable inner barrier
- Permeable outer membrane
- Stroma contrains carbohydrate enzymes
- Thylakoid is a highly folded vesicle
What is the structure of a chloroplast? (7)
Chloroplast envelope Thylakoid (membrane and space) Stroma Grana Strach granules Nuceloid Ribosomes
What is the principle photoreceptor?
Chlorophyll
What is chlorophyll also known as?
Light harvesting complex
How is light energy transferred to chemical energy?
Electromagnetic radiation is propagated as ‘photons’ (photooxidation)
What are the 2 reaction centres in photosynthesis and what do they do?
Photosystem 2 - oxidises H2O (P680)
Photosystem 1 - reduces NADP+ (P700)
How do electron pass from PS2 to PS1?
Electron transport chain
What light does PS1 respond to and what does this stimulate it to do?
<700nm
Creates biosynthetic reducing power in the form of NADPH
What does the cytochrome b6f complex do? (3)
Electrons travel from PS2 to PS1
Homologous to complex 3 (oxidative phosphorylation)
Generates a H+ gradient
What light does PS2 respond to and what does this stimulate it to do? (3)
<680nm
Generates a molecule of O2
Transfers e- from H2O to plastoquinone
Generates a H+ gradient
What is the structure of PS2 and where is it located?
Large protein assembly - 20 subunits Thylakoid membrane (Stroma/ TM / Lumen)
What are the key processes that occur in PS2?
Catalyses that transfer of e- from H2O to plastoquinone
P680+ (light) extracts e- from H2O
What is the equation in PS2?
2Q + 2H2O –(light)—> O2 + 2QH2
Why are electrons transferred from H2O to QH2?
QH2 e- are at a higher redox than in H2O
How does light P680nm extract e- from H2O? (4)
- Oxygen evolving complex
- Each time photon kicks electron from P680, e- are extracted from Mn
- 4 photons absorbed to extract 4 e-
- 4 e- used to reduce Q2 to QH2
What is occurs in PS2 that is vital for e- transfer?
Proton gradient
What does the cytochrome bf complex do?
Catalyse the transfer of e- from QH2 to plastocyanin
What occurs in the 2nd half of the Q cycle? (3)
Cytochrome bf reduces plastoquinone to plastoquinol
- takes up 2 H+
- oxidation, 2H+ released on stromal side
What is the proton gradient aided by?
Enzyme positioning
What is the structure and location of PS1?
Transmembrane complex - 14 polypeptides
Thylakoid membrane
What are the 3 activities that happen in PS1?
- E- from P700
- Ferredoxin contains FeS centre, transfers e- to NADP+
- P700 captures e- from reduced PC
