Relationship between wavelength and energy content
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; PIGMENTS ARE 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; THEY ARE 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 excited state of chlorophyll resulting from absorption of photons. • What happens
•
of light? Energy excites an electron! Chlorophyll has 2 excited states
the
when chlorophyll absorbs a photon
Excited electrons are used to do workmake ATP • 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 photon of light, the pigment must have an excited state, the energy of which matches the energy of the photon (ie energy gap must = energy of photon) • Why is chlorophyll green? There is no intermediate excited state between the blue and the red; the red and blue photons are absorbed, but the green photon is not. Key features of eyespot that allow for directionality and amplification of light signal • 2 types of channelrhodopsin; LOCATED ON PLASMA MEMBRANE; one absorbs better than the other • These orange globules are found in the chloroplast and are filled with carotenoid • 2 features of the orange globules= DIRECTIONALITY AND AMPLIFICATION: they have the ability to amplify the strength of the light AND tell Chlamy where the light is coming from • Chlamy can turn to block light • The orange globules amplify the light environment; they shade the photoreceptor • Orange globules actually reflects blue light, even though carotenoids absorb blue light Distinctions between photochemistry & photoisomerization • Photoisomerization: Photon excites one of the pi-bonding electrons, and once in the excited state, the molecule can swivel and alter its conformation, going between trans and cis. • Conformation change in pigment=conformation change of protein attached to said pigment • Photochemistry: Bonds are being formed/broken (creating an entirely new molecule, not just an isomer) •
Major similarities and differences between phototransduction in eyespot vs eye. • (EYESPOT) Chalmy: trans to cis • (EYE) Channelrhodopsin: cis to trans • (EYESPOT) Channelrhodopsin absorbs light and directly alters ion flow: channel goes form closed to open and allows ions to flow • (EYE) But in eye, light activates a pathway that eventually changes ion movement into and out of the cell: doesn’t DIRECTLY change the flow, but it activates a single transduction pathway that eventually does • Channelrhodopsin=direct • Eye: contains components in between • But the photoreceptors are incredibly similar Reasons why life has evolved to detect the narrow band of energy represented by “visible light”. • The reason ALMOST ALL organisms use visible light is because visible light has the perfect energy wavelength required to excite the electron • Ie microwaves cant excite electrons, they are only sufficient to slightly move the molecules around (too weak), whereas ionization energies such as gamma rays actually destroy the pigment/cell (too strong) • Thus shorter wavelengths are too strong and longer wavelengths are too weak Basics of bioluminescence. • Bioluminescence: ability to make your own light • We know photon excites electron using energy of a chemical form (ie ATP), but bioluminescence works the other way: you start at the excited state and when the electron decays, a photon is released into the environment in the form of light • There is a cost to this: energy of ATP is used to excite electron
Four “fates” of excited state of chlorophyll resulting from absorption of photons. • What happens
•
of light? Energy excites an electron! Chlorophyll has 2 excited states
the
when chlorophyll absorbs a photon
Excited electrons are used to do workmake ATP • 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 photon of light, the pigment must have an excited state, the energy of which matches the energy of the photon (ie energy gap must = energy of photon) • Why is chlorophyll green? There is no intermediate excited state between the blue and the red; the red and blue photons are absorbed, but the green photon is not. Key features of eyespot that allow for directionality and amplification of light signal • 2 types of channelrhodopsin; LOCATED ON PLASMA MEMBRANE; one absorbs better than the other • These orange globules are found in the chloroplast and are filled with carotenoid • 2 features of the orange globules= DIRECTIONALITY AND AMPLIFICATION: they have the ability to amplify the strength of the light AND tell Chlamy where the light is coming from • Chlamy can turn to block light • The orange globules amplify the light environment; they shade the photoreceptor • Orange globules actually reflects blue light, even though carotenoids absorb blue light Distinctions between photochemistry & photoisomerization • Photoisomerization: Photon excites one of the pi-bonding electrons, and once in the excited state, the molecule can swivel and alter its conformation, going between trans and cis. • Conformation change in pigment=conformation change of protein attached to said pigment • Photochemistry: Bonds are being formed/broken (creating an entirely new molecule, not just an isomer) •
Major similarities and differences between phototransduction in eyespot vs eye. • (EYESPOT) Chalmy: trans to cis • (EYE) Channelrhodopsin: cis to trans • (EYESPOT) Channelrhodopsin absorbs light and directly alters ion flow: channel goes form closed to open and allows ions to flow • (EYE) But in eye, light activates a pathway that eventually changes ion movement into and out of the cell: doesn’t DIRECTLY change the flow, but it activates a single transduction pathway that eventually does • Channelrhodopsin=direct • Eye: contains components in between • But the photoreceptors are incredibly similar Reasons why life has evolved to detect the narrow band of energy represented by “visible light”. • The reason ALMOST ALL organisms use visible light is because visible light has the perfect energy wavelength required to excite the electron • Ie microwaves cant excite electrons, they are only sufficient to slightly move the molecules around (too weak), whereas ionization energies such as gamma rays actually destroy the pigment/cell (too strong) • Thus shorter wavelengths are too strong and longer wavelengths are too weak Basics of bioluminescence. • Bioluminescence: ability to make your own light • We know photon excites electron using energy of a chemical form (ie ATP), but bioluminescence works the other way: you start at the excited state and when the electron decays, a photon is released into the environment in the form of light • There is a cost to this: energy of ATP is used to excite electron
