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Lecture 2

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Department
Biology
Course
Biology 1002B
Professor
Tom Haffie
Semester
Winter

Description
Lecture 2: Light: Energy & Information  The energy of the life is inversely related to the wavelength  Shorter wavelength = more energy Pigments absorb light  Has to take energy of the photons and trap the energy in a molecule  Pigments absorb photons of light  Pigments have a conjugated system: double bond, single bond, double bond, etc.  Represent an abundance of electrons that are non-bonding pi orbital electrons  Readily available to be excited by a photon of light; ready to trap the light  Retinal is one exception where the electrons are non-bonding  Pigments aren’t free in the cell, it’s bound non-covalently to proteins to form pigment-protein complexes  After centrifugation, you can see proteins stay attached to pigments Light absorption and emission  Chlorophyll has two possible excited states  Ground state; lower excited state; higher excited state  A blue photon will cause the electron to rise to the higher excited state because there’s a lot of -12 energy in the blue photon; instant heat loss (10 seconds); electron ends up in the lower excited state, which is exactly the state that the electron would be in if it was excited by a red photon  Whether you shine blue light or red light, the amount of energy available is always at the lower excited state, regardless of the colour of the light because the decay is so fast from the higher excited state to the lower excited state  One photon can excite one electron; photochemical equivalence  4 fates of excited state that are competing processes  Heat loss: decays back to ground state  Lose just a little energy as heat, and get to a sub-excited state, and lose the rest as fluorescence  Always deep red and has slightly longer wavelength than the wavelength that the electron can absorb due to the lost heat  Photochemistry: use the energy to do work -> carbon fixation, etc.  Energy transfer: transfer energy to another molecule  There is no green excited state; there is no excited state that can absorb the green photon, that’s why chlorophyll is green  The energy of the photon must perfectly match the energy required to go from ground sate tot eh excited state Phototransduction vs. Photosynthesis  Photochemistry is essential for both of these  Photochemistry occurs in the photoreceptor  The photon is driving the isomerization of retinal (photochemistry)  The unit of photochemistry in the retina is the photoreceptor  The unit of photochemistry for photosynthesis is the photosystem  Antenna on the outside, reaction centre in the middle  The photons can be absorbed by pigments in the antenna, and the energy is transferred to the reaction centre  The concept of the en
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