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Biology 1001A
Tom Haffie

Lecture 2 Electromagnetic Spectrum -gamma rays < x rays < ultraviolet radiation < near-infrared radiation < microwaves < radio waves -visible light= narrow region of entire EM Spectrum -light behaves like a wave: short wavelength (gamma rays) vs long wavelength (radio waves) -EM spectrum is separated based on wave length -energy of the light is inversely related to wavelength *** -gamma rays have more energy, have shorter wavelength -radio waves have less energy, longer wavelength -blue light has more energy than red light bc shorter wavelength -light as discrete particles of quanta; quanta blue light, quanta of red light -quanta aka photons (have a discrete, quantifiable amount of energy) -how much energy in photon of red vs blue light? More energy in blue vs red photon Pigments absorb light -in order to use energy, must absorb light -molecules which absorb light = pigments ex. Chlorophyll, indigo are both common with a conjugated system -conjugated system: alternation between a double to single bond; indicates a specific kind of electron configuration—many nonbonding electrons (Pi orbital electrons) -nonbonding electrons will interact with photons of light; not required for bonding thus readily accessible to track energy -Exception: retinal does involve bonding electrons **pigments are bound specifically to proteins; when you isolate a protein, you can keep pigment attached if careful enough --pigment protein complexes; pigment is bound noncovalently to protein; need to be careful when isolating, if too harsh then they will detach -protein electrophoresis: if isolate mitochondria proteins and isolate on the gel, must stain the gel with a blue dye and can visualize the bands -with pigment protein complexes don’t need to stain, able to run electrophoresis without staining; don’t want pigment to detached to proteins Light absorption and emission -what happens with a pigment molecule absorbs a photon of light? -single molecule of chlorophyll, for one pi nonbinding electron, floating around -electron can exist in ground state or two other excited states -for chlorophyll only 2 excited states; other molecules or pigments have 1- 8 -shine white light on single molecule of chlorophyll?? -if electron absorbs blue photon of light—enough energy to get electron into higher excited state **blue photon has a high amount of energy and is enough energy to get electron from ground state to higher excited state -chlorophyll with electron in a higher excited state—loose some energy as heat very quickly (10^-12 s) heat loss -higher excitation state decays to lower excited state -blue photon absorbed, an electron in a higher excited state quickly reduces to lower excited state -this is exactly the state you would get if chlorophyll absorbed red photon—red photon doesn’t have as much energy and only gets you to lower excited state -**doesn’t matter if you absorb blue or red photon, energy is different, very fast after absorption—you are really dealing with the energy in lower excited state -what happens to the energy in lower excited state? 4 fates (ways) to get rid of (use) excited state (1) excited state decays, electron drops back down to ground state and you lose heat—if pigment is in chlamydomas, if all the energy was lost as heat, the cells would heat up and die, there cant be a lot of heat lost in normal conditions (2) even from lower excited state you can lost a bit of energy as heat; decay a little bit to subexcited state, then you can lose the remainder energy (fluorescence- emission of light)—this is a different red, since we’ve lost some energy to heat, wavelength of this light is a little longer in wavelength, slightly lower energy bc some energy was lost in heat **fluorescence emissions slightly longer wavelength, lower energy (3) can do work with light (the entire point to trap energy and do work); work is photochemistry (use light to change the structure of a pigment) (4) transfer energy of excited state pigment to neighbouring pigment -Why is chlorophyll green in colour? Bc there is no green excited state (no excited state between blue and red photon absorption) if there was then chlorophyll would be able to absorb green light -but its not bc no green excited state; so green photons are lost, chlorophyll cannot absorb it; so photon is either reflected or transmitted through pigment Albert Einsten & Stark experiments -if you have one electron and one photon -one photon can excite one electron (1:1); energies must match -a photon cannot excite more than one electron; cant have 4 photons excited one electron -for energy to be absorbed, to trap the photon, the energy in photon must match the amount of energy required to get from ground state to lower excited state; to absorb a red photon, energy in red photon must match energy difference between ground state and lower excited state: REQUIRED for absorption to take place; which is why green photons don’t get absorbed, energies don’t match, there is no excited state here—green photons have more energy than lower excited state, and less energy than higher excited state, they don’t match so the photon is not absorbed -above explains absorption spectrum, re: look at photosynthesis chapter, -look at graph of absorption spectrum as a function of wavelength; turn graph on side to understand better -ex. chlorophyll -high absorption in blue, less absorption in red -fluorescence emission spectrum -strong absorption band in the blue represents excited state; absorption in red represents other excited state -fluorescence emission shifter to longer wavelength; is decay from other excited state -absorption characteristics reflect excited states of pigments Phototransduction vs Photosynthesis -photochemistry—whether you want to use this for vision or photosynthesis there must be a photochemical event -look at discs in the rod, the photochemical event takes place in the photoreceptor molecule itself (molecule in the membrane) -actual photochemical event is the isomerization of pigment retinal -photosynthesis is different -structural unit of light capture and photochemistry in photosynthesis is called photosystem -much more light capturing in photosystem than in isomerization of retinal -photosystem comprised of two parts: (1) deep purple antenna—purple is protein, chlorophylls are individually bound to protein—surrounds… (2) reaction centre is in the middle, has special chlorophyll molecule -antenna= lots of pigment proteins; no photochemistry of photosystem; simply energy transfer as distinct from photochemistry -ex. Chl* + Chl  Chl + Chl* -Chlorophyll is absorbing a photon of light: electron gets excited to higher energy state, which is excited state chlorophyll (Chl*) -ENERGY TRANSFER: fate of excited state is that energy can transfer from a chlorophyll to a neighbouring chlorophyll; electron goes back down to a ground state and transfer to another chlorophyll -for this to occur, think about atomic distances, 6 angstroms between pigments; 2 pigments, one absorbs a photon of light, becomes excited and energy from excited s
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