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Lecture 2

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Western University
Biology 1002B
Tom Haffie

Lecture 2: Light: Energy and Information  Electromagnetic spectrum o Shorter the wavelength, the more energy it has, the longer it is the less energy it has o The energy of the light is inversely related to the wavelength o Light behaves like wave and particles, photons (packages of light, fixed amount of energy)  Pigments absorb light o The pigments absorb light because of the conjugated bonds, (double, single, double, single etc.) o Non-bonding Pi orbital electrons, they are available if needed to trap more light = more energy o Pigments don’t move around, they are bonded noncovalently to Pigment-protein complex, can resolve them in gel electrophoresis  Light absorption and emission o In chlorophyll there are 2 excited states, (higher and lower excited state) o Blue photon can excite the electron in chlorophyll to the higher excited state o One photon can only excite one electron o Lose energy to heat (10^-12 s) and the electron is ended up in the lower excited state, will be the same as the chlorophyll absorbed a red photon o Does matter what light is shined, regardless it’s all in the lower excited state because the decay from the higher excited state is just too fast o There are 4 fates of this lower excited state  Decay back to ground state through loss of heat  Loss a little as heat/energy and loss the rest as fluorescence (deep red, shift to a slighter longer wavelength because it lost a little bit of heat)  Photochemistry  Energy transfer o There is more fluorescence is more in the extracted chlorophyll compared to the not extracted chlorophyll  Chlorophyll has no green excited state cannot absorb the green photon,  The energy of the photon must match the energy of the pigment, if it does not match perfectly, it will not absorb it  Phototransduction versus photosynthesis o Photochemistry, where it takes place?  Looking at the rods and cones  Occurs in the photoreceptor  Isomerization of retinal  Photosynthesis
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