Lesson 3 photosynthetic pigment extraction
Transcript of Lesson 3 photosynthetic pigment extraction
Photosynthetic pigment extraction
(f) define the term photosynthetic pigment;(g) explain the importance of photosynthetic
pigments in photosynthesis;
What colour should plants growing below the surface of water be??
• Light intensity varies hugely with depth.• Why does the intensity get lower as water depth increases?
Light absorption by chlorophylls
• All chlorophyll is associated with proteins to form light-harvesting complexes in the thylakoid membrane
• There is no free chlorophyll
Structure of LHCII trimer
Kühlbrandt et al. (1994) Liu et al. (2004)
LHCII trimers in grana stack
Light is absorbed by individual chlorophylls in the light-
harvesting complexes
Energy is transferred from one pigment to another via Resonance Energy Transfer
This transfer funnels the energy to a reaction centre where
electron transfer starts
Energy transfer in light-harvesting complexes
Analysis...
Rf value = distance pigment travelled distance solvent travelled
• Carotene (yellow/orange) 0.98• Xanthophylls (yellow) 0.15 or 0.28• Chlorophyll a (yellow/bright green) 0.59• Chlorophyll b (olive or blue/green or yellow/green) 0.42• Pheophytin (olive green) 0.81• Anthocyanin (red/pink/purple/blue) 0.32-0.62
• Photon of light strikes accessory pigment• Light energy is passed down to the reaction centre• 2 electrons are excited and released from the Mg atom
PSI = chlorophyll a P700nmPSII = chlorophyll b P680nm
Low resolution structures of photosystem II
• electron microscopy• membrane preparations• single particles - negative stain
arrangement in thylakoid membrane
Photosystem II - at 3.5Å resolution