Photosynthesis Flashcards
Name the 4 structural regions of the chloroplast
- Envelope (pair of outer limiting membranes)
- Stroma (unstructured background matrix)
- Thylakoids (highly structured internal system of membranes)
- Lumen (intra-thylakoid space)
Thylakoids
- Can be stacked (appressed) or unstacked (non-appressed)
- Provides network of interconnections between grana
- Contains chlorophyll and carotenoid pigments
- The site of light dependent energy conserving reaction
Name the 4 major protein complexes in the thylakoid
- Photosystem II
- Cytochrome b6f complex
- Photosystem I
- ATP synthase
What is the redox reaction?
Energy transfer from one molecule to another (reduction and oxidation)
What is OILRIG?
Oxidation is loss of electrons (oil) and reduction is gain of electrons (rig)
Photosystem II (PSII)
- Multi-subunit protein complex
- Contains 300 chlorophyll molecules
- Light harvesting complex (LHC)
- Reaction centre core
- D1 and D2 proteins
- Oxygen evolving complex
Light transfers
Energy is transferred to pigments which absorb light until it reaches the reaction centre in PSII which transfers an electron to an electron acceptor
What reaction is carried out by the oxygen evolving complex in PSII?
2 H20 = O2 + 4H+ + 4e-
PSI reaction centre
Excites electrons and sends them to electron acceptor and stored in NADPH
What is oxidative phosphorylation?
High energy molecules in PSI cause proton molecules to flow down a gradient to produce ATP
Proton gradient across thylakoid membrane
- 3 pH units
- Lumen is more acidic than stroma
- NADPH is produced and proton gradient is used to produce ATP
Light dependent photosynthesis
Produces ATP and NADP
Dark reactions
ATP and NADPH make sugars from CO2
What is carbon fixing?
- Requires high energy molecules
- Fixed into carbohydrates via Calvin-Benson cycle
What are the 3 stages of the Calvin cycle?
- Carbon fixation
- Reduction of 3-PGA
- Regeneration of RuBP
What is the use of carboxylase in the Calvin cycle?
Produces 2 molecules of PGA
What is the use of oxygenase in the Calvin cycle?
Produces 1 molecule of PGA and PG
What is photorespiration?
- Uses oxygen instead of CO2
- Competes for reaction at the same site as enzyme
- Produces phosphoglycerate instead of carbon fixing
Important steps of Calvin cycle
- RuBP joins with CO2 to give 2 molecules of 3-PGA
- Enzyme that carries out first step is called RUBISCO
- Energy in the form of ATP and NADPH
- G3P can be used to make hexose sugars
- Most G3P is recycled back to RuBP
- Reaction occur in the stroma
