Photosynthetic pigments...

Learning objectives...•The roles of pigments in light

harvesting

http://www.teachers-direct.co.uk/resources/quiz-busters/quiz-busters-game.aspx?game_id=28036

• 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

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

Low resolution structures of photosystem II

• electron microscopy

• membrane preparations

• single particles - negative stain

arrangement in thylakoid membrane

Photosystem II - at 3.5Å resolution

Prosthetic groups of PSII core

• The 2 most important pigments involved in photosynthesis are chlorophylls and (1). The chlorophyll molecule consists of a complex ring called a (2) ring that is attracted to water so called (3). It also has a long lipid-soluble chain that is repelled by water and therefore called (4). Chlorophyll takes in certain wavelengths more than others. A graph of the amount of light taken in by different pigments is called the (5). Chlorophyll a acts as the (6) centres at the heart of the a complex of pigments molecules and associated (7) know collectively as a photosystem. Around the central chlorophyll molecule are (8) pigments that form a unit called a (9). Photosystem I has chlorophyll that absorbs light of wavelength (10) and found mostly in the (11) of the chloroplast. Photosystem II has chlorophyll that absorbs light of wavelength (12) and is found mainly in the (13).