Intro lecture Flashcards
How to grow better wheat
Enhance mechanisms giving off O2 (photosyn)
What is photosynthesis
Capture and use of light energy by organisms
What are reaction centres
Chlorophyll based, electron transfer, photochemistry, oxygenic and anoxygenic versions
Rhodopsin homologues use
Cis/trans retinal isomerisation - proton pumping
The two major types of photosynthesis
- Rhodopsin based 2. Reaction centres
How does rhodopsin based photosynthesis work
Uses photons of light to pump protons across membrane - generates protonmotive force used to drive ATP synthesis but not enough for organism to grow as doesn’t fix carbon
Retinal cofactor
Covalent Schiff base to Lys216 - 7 TM helix protein homologous to GPCR
What drives proton pumping in rhodospin homologues
Isomerisation from trans to cis - external reductant needed
Photosynthetic RX centre facts
All derived from common ancestor, membrane proteins, dimers, core of 5 TM helices, bind Chl, do photochemistry, donor oxidised, acceptor reduced, has other cofactors
PSI RC terminal electron acceptor
FeS
PSII RC terminal electron acceptor
Quinone
When did oxygenic photosynthetic bacteria arise
About 2 billion years ago
When did anoxygenic photosynthetic bacteria arise
About 3.2 billion years ago
How do green photosynthetic anaerobes work
Use H2S in photosynthesis to generate sulphur
Where did oxygenic photosynthesis evolve
Cyanobacteria
What are cyanoobacteria
Oxygenic phototrophs - internal membranes (thylakoid membranes) contains membrane protein complexes of the light RX
Where were chloroplasts derived from
Endosymbiosis of cyanobacterium
Where do light and carbon reactions take place
Chloroplast
How long is a chloroplast
5 micrometres
Thylakoid membrane organisation
PSI and ATP synthase located in stromal lamellae. PSII found in granal regions. Cytb6f found evenly distributed throughout membrane
What is eukaryotic photosynthesis done by
Endosymbionants
How many photons absorbed per chl per second
10 - inefficient
Antenna
Couple thousands of pigments to single RC so RC is excited many times per second
How does RC work
- Absorb photon - antenna pigment becomes excited
- Exciton can jump around antenna
- Small upward energy jumps possible but mainly downward
- Exciton diffuses around antenna but ends up in RC
What does light absorption lead to
Photoinduced charge separation
Major pigments
Chl a (CH3) and b (CHO)
Examples of accessory pigments
Carotenoids, bilins
What is the main light harvesting protein in plants
LHC2
What are major light harvesting proteins of cyanobacteria
Phycobiliproteins
