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Lecture 2: Light Energy and Information; Lecture Outcomes.docx

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Western University
Biology 1002B
Tom Haffie

Lecture 2 Outcomes Relationship between wavelength and energy content of a photon. • Light behaves as discrete particles of energy: we call these particles photons or quanta (packages of light); they have no mass, but they have energy • Wavelength is inversely proportional to energy (ie the energy of a photon is inversely related to its wavelength) • Photon of blue light (short wavelength) has more energy than a photon of red light (long wavelength) • Proteins don’t absorb light • Pigment absorbs light from the visible spectrum (not damaging) Molecular characteristic of pigments that make them able to absorb light. • Channelrhodopsin is a protein; it does NOT absorb light • Thus channelrhodopsin must have a pigment associated with it that actually absorbs the light • It is important to note that pigments don’t just float freely; PIGMENTSARE COVALENTLY BONDED TO PROTEINS • Pigments absorb light because they have a conjugated ring system: alternating bonding of double-single-double bonds • CRS is a very planar shape that provides non-bonding electrons (delocalized electrons) • These electrons are available to interact with photons of light; THEYARE NOT INVOLVED IN BONDING Relationship between pigments and associated protein. • See above • Proteins provide organization to pigments • Most proteins (ie in mitochondria or cytosol) don’t have pigments associated with them • We usually stain proteins via blue dye Four “fates” of the excited state of chlorophyll resulting from absorption of photons. • What happens when chlorophyll absorbs a photon of light? Energy excites an electron! • Chlorophyll has 2 excited states • Excited electrons are used to do workmakeATP • Environment of the pigment dictates which process is going to occur more of the time • 1) Heat Loss: losing all energy, doesn’t happen very often • 2) Fluorescence: you lose a little of the excited state thus wavelength becomes smaller =higher energy • 3) Photochemistry: using excited state to get work done, such as break bonds; happens more than anything else • 4) Energy Transfer: if two pigments are close enough together, excited state can fall to neighbouring pigment; electron doesn’t actually move, you’re simply moving energy; this is NOT oxidation or reduction. Relationship between energy of photon and electron excited states to explain pigment colour and absorption spectrum. • HOW does pigment interact with the photon? • Step 1) Photon must be absorbed by the pigment • Step 2) photon excites an electron in pigment from ground state to higher state • 1 photon of light can excite only 1 electron; this is called Photochemical equivalence • For a pigment to absorb a p
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