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Chapter 1

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BIOL 1000
Tamara Kelly

BIO 1000 Notes Chapter 1.1 Notes: • Light function #1: Source of energy that directly or indirectly sustains organisms. • Light function #2: [Source of info] Provides organisms with info about physical world that surrounds them. • Ex: Green alga Chlamydomonas = uses light for both energy and information • Sun releases electromagnetic radiation(differentiable by their wavelength-distance between two successive peaks) Wavelength = measured in nanometers (10^-9 m) Light: Portion of the electromagnetic spectrum that humans can detect with their eyes. Photons: Stream of energy particles (light composed of this) LIGHT = wave of photons. • Wavelength & Energy inversely related (SHOWN BELOW): • The longer the wavelength = the lower the energy of the photons it contains. • Shorter wavelength blue = consists of photons of higher energy than red light. • 380(400) - 700(750) = visible light = wavelengths we can see. • Light interacts with matter, when photon hits object, photon has 3 possible fates: • 1. Reflected off object 2. Transmitted through object 3. Absorbed by object(must take place if photons want to be used as a source of energy or info) moved from ground state to excited state(higher-energy level)electron within molecule. Electron • NOTE: proton only absorbed by electron if photon energy =’s energy difference between electron’s ground state & excited state. If not = photon transmitted through molecule or reflected. • EXCITED STATE ELECTRON = source of energy required for photosynthesis & vision. Eyespot: Allows individual cells to gather info about location & intensity of light source (light sensor) DOES NOT GENERATE AN IMAGE---Eye does that. Pigments: Major class of molecules that ar very efficient at absorbing photons (light absorbers) • Ex: chlorophyll a(involved in photosynthesis), 11-Cis-retinal(involved in vision), indigo(dye jeans blue), Carmine, Beta-Carotene • Pigments absorb light at different wavelengths (cause they differ in # of excited states available to excitable electrons) Ex: Pigment absorbs only blue photons cause they have only one high-energy excited state. • May look different but all have CONJUGATED SYSTEM. BIO 1000 Notes Conjugated System: A bonding arrangement/region where carbon atoms are covalently bonded to each other with alternating single & double bonds. RESULTS in delocalization of electrons(electrons not attached to particular atom or bond in a molecule). CRITICAL TO LIGHT ABSORPTION. • PIGMENTS COLOUR = result of photons of light it does NOT absorb(instead reflected or transmitted through pigment to reach our eyes) Chapter 1.2 Notes: • 1. Light absorbed 2. Potential energy of excited electrons within pigment molecules used in photosynthetic electron transport to synthesize NADPH & ATP 3. Molecules consumed in Calvin cycle of photosynthesis to convert CO2into carbohydrates(sugar) & release O 2 • Photosynthetic apparatus of a C.reinhardtii cell absorbs millions protons/second. • Cellular respiration breaks down carbohydrates, trapping released energy as ATP PHOTOSYNTHESIS(rate of O relea2e) increases in blue/yellow/red light. Not green as MOST(some is) is reflected not absorbed or transmitted(Why plants green). • Not all organisms that use light as source of energy are photosynthetic(don’t use light energy to convert CO 2nto carbohydrates). Ex: Halobacterium(hypersaline enviro) have pigment-protein complex called bacteriorhodopsin(light-driven proton pump). Its pigment component(retinal) = captures photons of light that provide energy supply to pump protons out of cell(creates difference of H+ concentration across plasma membrane = source of potential energy used by ATP synthase to convert ADP to ATP) Chapter 1.3 Notes: Photoreceptor: The basic light sensing system • Most common in nature = Rhodopsin(basis of vision in animals, in C.reunhardtii serves as light-sensing unit of the eyespot) -- structurally similar & evolutionarily related to bacteriohodopsin found in Halobacterium Rhodopsin Molecule: Consists of opsin(protein) that binds to retinal(single pigment molecule & derivative of Vitamin A) RHODOPSIN = in bacteria & humans. Opsin: Membrane proteins that span a membrane multi times and form complex with retinal molecule at the centre. • Absorption of photon of light = retinal pigment molecule change shape(straightens- shape matters) = triggers alteration to opsin protein = alterations in intracellular ion concentration & electrical signals. ULTIMATELY THEN trigger signaling events, which allows organism to respond to the light. • Some organisms can sense light without eyes (Plants,Algae,Invertebrates, some prokaryotes). Eyespot of C.Reinhardtii = found within chloroplast in region associated with cell membrane. Composed of 2 layers of carotenoid-rich lipid globules(focus & direct incoming light toward photoreceptors) BIO 1000 Notes • Eyespot has no role in photosynthesis = instead photoreceptors allow cell to sense light direction & intensity (ex: move away from predators) • Using flagella, C. respond to light by swimming toward or away from light(called phototaxis) • Phototaxis = allow cell to stay in optimum light environment to maximize light capture for photosynthesis • Light absorption(eyespot) = linked to swimming response by a signal transduction pathway(light absorption triggers change in ion concentration(k,ca), which generate electrical events THAT change beating pattern of flagella. Phytochrome: Photoreceptor in plants that senses the light enviro & essential for photomorphogenesis(normal developmental process activated when seedlings exposed to light • present in cytosol of all plant cells. seedlings exposed to wavelengths of red light = phytochrome becomes active & starts signal transduction pathway that reaches nucleus. • In nucleus = signals activate genes which code for proteins involved in photo & leaf develop - ABSORB RED LIGHT. CONTAIN chromophore which are linked to proteins Differentiation between eye of invertebrate & eyespot of C.Reinhardtii: • Vision. Vision needs eye to focus & absorb light but also brain(or simple nervous system) to interpret signals from eye. WE SEE WITH OUR BRAIN NOT EYES. Ocellus: Simplest eye, consists of a cup or pit lined with up to 100 photoreceptor cells. • Photoreceptor cell = is a modified nerve cell that contains thousands of individual photoreceptor molecules. • Flat worms of genus Planaria contain ocelli = allows them to orient themselves in response to light • Eye of planaria not much more advanced than eyespot of C.Reinhardtii = both sense light intensity & direction to a light source. 2 types of image-forming eyes: 1. Compound eyes = Built of 100‘s of ommatidia(individual units) fitted together. Common in arthropods(insects&crustaceans). Incoming light focused onto bundle of
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