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Lecture 2

Biology 1002B Lecture Notes - Lecture 2: Photochemistry, Chlorophyll, Photon

Course Code
BIOL 1002B
Tom Haffie

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Lecture 2 Outcomes
1. Relationship between pigments and associated protein.
Pigments are never free in the cell, always attached to proteins
If pigments are free in the cell, can’t transduce the light to do anything
Pigment is what changes and and for it to do anything, the pigment change in
structure has to cause a protein change in structure
2. Four “fates” of the excited state of chlorophyll resulting from
absorption of photons.
Lose the energy as heat to the environment (excited state decays to ground
Fluorescence: pigment spits out the photon
Photochemistry: using light to drive a chemical change
Energy transfer: photosystems with chlorophyll pass on the energy of the
electron (not an oxidation reaction  just passing of energy)
3. Relationship between energy of photon and electron excited states
to explain pigment colour and absorption spectrum.
Blue light absorbed: electron goes to high excited state
Red light absorbed: electron goes to lower excited state
Strong absorption for red and blue
Not having capacity to absorb green light (green photon passing through)
gives chlorophyll its colour.
4. Distinctions of photochemistry between phototransduction (vision,
eyespot...) & photosynthesis
Phototransduction (vision, eyespot):
oUsing energy of light to change a bond in the photoreceptors
oIsomerization of retinal
oOxidization of chlorophyll
oOxidizing an electron that is already in an excited state
oElectron leaving is a photochemical event
5. Major similarities and di+erences between phototransduction in
eyespot vs eye.
Channelrhodopsin and rhodopsin are similar structurally which be due to
homology but functionally they do very di-erent things.
Channelrhodopsin is a membrane pore that closes and opens channels.
Rhodopsin is not a pore:
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