Rebecca Davenport10/24/16BIOL 1406- BW1Ch 10 blueprint1. Part 1: Photosynthesis- the process that converts solar energy into chemical energy.a. Photo = light, Synthesis = to build; photosynthesis uses light energy to build sugars.b. Why is photosynthesis important? i. Directly or indirectly, photosynthesis nourishes almost the entire living worldc. Where does it occur? chloroplastsi. In plants, algae, certain other unicellular eukaryotes, and some prokaryotes.ii. Does NOT occur in just plants****d.e. Chemical reaction of photosynthesis:i. 6 CO2 + 12 H2O + Light energy → C6H12O6 + 6 O2 + 6 H2O ii. Chloroplasts split H2O into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules and releasing oxygen as a by-productiii. Reverses the direction of electron flow compared to respirationiv. Redox process in which H2O is oxidized and CO2 is reducedv. Endergonic process; the energy boost is provided by lightvi. Purpose: vii. Light energy viii. To build (sugar)ix. Stage x. Light reactions (linear electron flow)xi. Calvin cyclexii. Input xiii. Light energy (photon), waterxiv. CO2xv. output xvi. ATP, O2 (oxygen is waste), NADPHxvii.1 G3Pxviii. location xix. Thylakoid membranexx. Stroma xxi.f. Two stages of photosynthesis:i. Light reactions- the photo part1. Occurs in the thylakoid membrane2. Split H2O & Release O23. Reduce the electron acceptor NADP+ to NADPH4. Generate ATP from ADP by photophosphorylationii. Calvin cycle- the synthesis part1. In the stroma2. Forms sugar from CO2, using ATP and NADPH3. Begins with carbon fixation, incorporating CO2 into organic molecules.4. Requires both NADPH and ATPg. Site of photosynthesis in plants-i. Leaves (and other green areas) are the major locations of photosynthesisii. Chloroplasts are found mainly in cells of the mesophyll, the interior tissue of theleaf1.iii. CO2 enters and O2 exits the leaf through microscopic pores called stomataiv. A chloroplast has an envelope of two membranes surrounding a dense fluid called the stromav. Thylakoids are connected sacs in the chloroplast which compose a third membrane system (stacks = grana)vi. Chlorophyll, the pigment which gives leaves their green color, resides in the thylakoid membranes.vii.2. Autotrophs sustain themselves without eating anything derived from other organismsa. “Producers” make organic molecules from CO2 and other inorganic moleculesb. Photoautotrophs use the energy of sunlight to make organic moleculesi. Carbon source is CO2.3. Heterotrophs obtain their organic material from other organismsa. Heterotrophs are the “consumers” of the biosphereb. Almost all heterotrophs, including humans, depend on photoautotrophs for food and O2c.d.4. Part 2: Nature of lighta. The Nature of sunlight-i. Light travels in rhythmic wavesii. Wavelength is the distance between crests/peaks of wavesiii. The electromagnetic spectrum is the entire range of electromagnetic energyiv. Visible light consists of wavelengths that produce colors we can seev.vi. Photons are quantities of light energyb. Photosynthetic pigments: The light receptorsi. Pigments are substances that absorb visible lightii. Different pigments absorb different wavelengthsiii. Wavelengths that are not absorbed are reflected or transmittediv. An absorption spectrum is a graph plotting a pigment’s light absorption versus wavelengthv. An action spectrum profiles the relative effectiveness of different wavelengths of radiation in driving a processc. Pigmentsi. Chlorophyll a is the main photosynthetic pigmentii. Accessory pigments, such as chlorophyll b, broaden the spectrum used for photosynthesisiii. Accessory pigments called carotenoids absorb excessive light that would damage chlorophyll (photoprotection)d. Excitation of chlorophyll by lighti. When a pigment absorbs light, it goes from a ground state to an excited state, which is unstablee.5. Part 3: Light Reactions a. Photosystem- consists of a reaction-center complex (a type of protein complex) surrounded by light-harvesting complexesi. The light-harvesting complexes (pigment molecules bound to proteins) transfer the energy of photons to the reaction centerii. Water is considered source of energy.b. Linear electron flow- the primary pathway, involves both photosystems and produces ATP and NADPH using light energy.i. Two possible routes for electron flow:1. Cyclic-a. Electrons cycle back from Fd to the PS I reaction centerb. Uses only photosystem I and produces ATP, but not NADPHc. No oxygen is releasedd. May protect cells2. Lineara.b. Water is source of all electronsc. KNOW WHICH IS P680 AND P700!!!!ii. Photosystems = iii. Light harvesting complex +iv. Reaction centerv. vi. Pigments and carotenoidsvii. Primary electron acceptorviii. ix. x. Pair of “special” chlorophyll moleculexi. 8 steps involving two photosystems and two electron transport chains.xii.6. Part 4: Calvin cyclea. Regenerates its starting material after molecules enter and leave the cycleb. Builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPHc. Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde 3-phospate (G3P)d. For net synthesis of 1 G3P, the cycle must take place three times, fixing 3 molecules of CO2e. The Calvin cycle has three phases:i. Carbon fixation- taking carbon from CO2 and attaching it to other molecules. 1. * CO2 attached to a 5-carbon molecule, RuBP, using the enzyme Rubisco to get 2 molecules of 3-phosphoglycerate2. RuBP + CO2 >>Rubisco>>3 Phosphoglucerate ii. Reduction1. *3-phosphoglycerate gets phosphorylated and reduced , loses its phosphate group to become G3P2. *For every three CO2 that enter the Calvin Cycle, 6 G3P are made, but only one exits3. * Uses 6 ATP and 6 NADPHiii. Regeneration of the CO2 acceptor (RuBP)1. *Carbon skeletons of 5 G3P rearranged to form 3 RuBP2. *Requires 3 ATPiv.f. Alternative mechanisms of carbon fixation:i. Dehydration is a problem for plants, sometimes requiring trade-offs with other metabolic processes, especially photosynthesisii. On hot, dry days, plants close stomata, which conserves H2O but also limits photosynthesisiii. The closing of stomata reduces access to CO2 and causes O2 to build upiv. These conditions favor an apparently wasteful process called photorespiration1. Photorespiration: a. In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a three-carbon compound (3-phosphoglycerate)b. In photorespiration, rubisco adds O2 instead of CO2
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