Photosynthesis Flashcards
What are the two types of photosynthesis?
Oxygenic photosynthesis - electron donor: H20, by-product: O2 (plants, algae, cyanobacteria)
Anoxygenic photosynthesis - electron donor: H2S, by-product: elemental S (green/purple ulcer bacteria)
What are the two phases of photosynthesis?
Light reactions - photosynthetic electron transport chain // conversion of light energy into chemical energy —> ATP & NADPH
Carbon reactions - CO2 fixation (“dark” reaction / Calvin cycle)
Chlorophyll is the main … pigments
light-absorbing
What is the structure of a chlorophyll?
- Tetrapyrrole ring (porphyrin)
- Metal cofactor (centre of porphyrin)
- Phytol tail (long, hydrophobic side chain, non polar)
Phycobilins is the main … in cyanobacteria & red algae
pigment
What is the structure of phycobilins?
- Linear tetrapyrroles
- No metal cofactor
- No phytol tail
The light in photosynthesis can return in 3 different ways, which ways?
- Relaxation - lost as heat
- Fluorescence - lost as light of longer wavelength
- Transfer - to neighbouring pigment
What is Anoxygenic photobionts?
One photosystem
What is Oxygenic photobionts?
Two photosystems
What is the Z-scheme?
How the two photosystems work together to convert light into ATP
Describe the photosynthetic electron transport chain
Works in series - two different photosystems (I & II) —> absorbs a certain amount of light —> energy of light is transferred from one chl-molecule to another —> arrives to the reaction centre
—> special chlorophyll (PSII = P680), all excitation energy —> high energy state —> lose energy = lose electron —> PS has a net positive charge from losing an electron —> gains an electron from the oxidation from H2O
What is the photophosphorylation?
Light-dependent synthesis of ATP
There are two multiprotein segments in the ATP synthase, which are they?
- Transmembrane complex - CF0
- Hydrophilic extrinsic complex - CF1
What happens in the carbon cycle (Calvin cycle)?
Photosynthetic carbon fixation (in Stroma)
How many steps/phases does the C3 calvin cycle include?
13 steps / 3 phases
Describe the three C3 Calvin cycle phases.
- Carboxylation (1 reaction): CO2 + RuBP —> 3-PGA
- Reduction (2 reaction) (required ATP & NADPH): 3-PGA —> triose phosphate (GAP)
- Regeneration (10 reactions) (Requires ATP): GAP —> RuBR
*Calvin cycle needs more ATP than NADPH
What happens to the triose phosphate? (C3)
First used for these biosynthetic pathways in photosynthetic cells (source cells)
What happens to the excess triose phosphate? (C3)
Transported as sucrose —> transported through the phloem from source (leaf) to sink cells
Where does CAM photosynthesis occur?
Common in plants that inhibit extremely arid areas
Problem - How to avoid water loss in a hot & dry habitat and still photosynthesis?
Solution - temporal separation of CO2 uptake & fixation
Night: stomata open - CO2 —> malate
Day: stomata closed - malate —> CO2 + pyruvate (Calvin cycle)
