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Lecture 2

Biology 1002 lecture 2 on LIGHT.pdf

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Western University
Biology 1002B
Tom Haffie

Lecture 2: Light Jan 10, 2013 • light behaves like a wave • visible light very small portion of light • the energy of light is inversely proportional to its wavelength more energy= shorter wavelength • • quanta or photon of light • photon has a descrete and quantifiable amount of energy • molecules that absorb light are called pigments • pigments have conjugated system (alternating double and single bond in ring) • • conjugated system have non bonding pi orbital electrons which are special because their electrons are always ready to absorb light? • pigments not free and floating in the cell but bound to proteins • if u isolate a protein carefully you can also get the pigment • the pigment is bound non covalently to the protein so you must be careful in your isolating behaviour • can run gel electrophoresis of proteins without stain when using pigment-proteins Lecture 2: Light Jan 10, 2013 Light Absorption and Emission • electron is excited into a higher state from ground state • eventually heat is lost (10 to the -12) and/or light is released (FLUORESCENCE IS SLIGHTLY LONGER WAVELENGTH THEN THE INTIAL WAVELENGTH) • the light can also do work called photochemistry • light can also transfer energy to another pigment • depending on which wavelength hits the electron it will enter into a lower or higher excited state Why is cholorphyll green? There is no green excited state for it to absorb green light so it reflected or transmitted through the pigment. • one photon excites one electron the energy must match the length it takes for a electron to reach its excited state
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