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Photosynthesis – Part II Spring 2013 - Althoff Reference: Mader & Windelspecht Ch. 7) • Plants as Solar Energy Converters • Plants as Carbon Dioxide Fixers Lec 08 Solar Energy & Wavelengths • There are 7 basic categories of radiant (aka solar) energy in the electromagnetic spectrum: gamma rays x-rays UV ___________________ infrared microwaves radiowaves • Visible spectrum: 380-750 nm (nanometers) Visible Light • Wavelengths different for ______________ Increasing wavelength Increasing ENERGY Absorption Spectrum for __________________ Pigments chlorophyll a chlorophyll b carotenoids For the record… • Notice that the different photosynthetic pigments have different absorption spectrums • Chlorophyll a and b have a wider “_________” range than carotenoids….as carotenoids do not have any absorption beyond approximately 500 nm. • Because of the wider absorption spectrum, chlorophyll a and b play “THE” ____________ roles in photosynthesis… • Carotenoids play an _____________ role. Non-cyclic pathway Electron flow in light reactions 3 2a 2 3a 4 1 4 4a Electron Flow…starting with the light reactions • ______________________– the route electrons usually travel during the ___________________. 1 2 • Starts with “Photosystem II” (although it happens essentially first). • Pigments absorb solar energy, then pass to other pigments until it is concentrated in a particular pair of ____________________ molecules—known as the “______________________” • Electrons (e-) become so energized that they escape the reaction center and move to nearby _________ _________________ Electron Flow…from light reaction to Calvin cycle reactions… • Water splits, releasing ____ into the atmosphere 3 4 • The H+ stays in the ________________ and contribute to the formation of the H+ gradient. • Electron acceptor sends __________ electrons down an electron transport chain. • Combined with ATP synthase complexes, ATP production occurs…which is then…. • Used by the ______________________ in the _________ to reduce CO2 to a carbohydrate simultaneously on the Calvin cycle reactions side… 2a 3a 4a • Energized electrons leave the reaction center, to the electron receptor… • to merge with NADP+ and H+ to form ________. This is on the ____________________ side…2 electrons are accepted here. • In the Calvin cycle reactions, the NADPH along with the ATP that came from the light reaction side _________ CO2 to CH2O (aka a carbohydrate) Organization of the Thylakoid Membrane • Photosynthesis II – pigment complex and electronacceptor molecules; releases O2 • Electron transport chain carries electrons from PS II to PS I via _______________. H+ • ________________ pumped from stroma into complex is an thylakoid space. enzyme that joins • Photosynthesis I – pigment ADP + P to make ATP complex and electron acceptor molecules reduces NADP+ to NADPH ATP Production • Thylakoid space acts as a ____________ for many H+. • As water is _____________, two H+ remain in the thylakoid space. • Result: __________ in thylakoid space than in the stroma…then flow of H + to from _____________ concentration provides kinetic energy that allows ATP synthase complex enzyme to join ADP + P. This method of producing ATP is called chemiosmosis— what we looked before (Chapter 6) • Summarized in next slide PS II PS I chemiosmosis Plants as Carbon Dioxide Fixers • Calvin cycle discovered by ______________ and colleagues, used radioactive isotope 14C as a tracer to “follow around” the reactions. • Photosynthesis uses CO2 from the ______________ to produce carbohydrates. • Question…how does the CO2 get into atmosphere in the first place??? Answer: when ____________ take in O2 they ______ CO2. Of course, the CO2 is produced by cellular respiration (the details starting after the next exam). • Carbon dioxide (CO2) fixation is the first step of the Calvin cycle. As shown in the next slide ________________ Reactions – details these ATP & NADPH produced by light reactions 1 2 these ATP produced by light reactions 3 The Calvin cycle reactions 1 2 • ___________– 1st step – molecule of carbon dioxide from atmosphere is attached to _____ (ribulose-1, 5bisphosphate), a 5-carbon molecule. The result is a 6-carbon molecule, which splits into two __________ __________. Enzyme that speeds up this reaction is RuBP carboxylase—a protein that makes up 20-50% of the content of chloroplasts. Large amount necessary because, compared to other enzymes it is rather slow acting. • ______________– 2nd step – first 3-carbon molecule is called 3PG (3-phosphoglycerate). Each of 2 3PG molecules undergoes reduction to make ____ (glyceraldehyde-3-phosphate)—in 2 steps The Calvin cycle reactions…con’t 3 • _________________ – 3rd step – in diagram on previous slide, notice Calvin cycle reactions are multiplied by 3 because it takes three turns of the Calvin cycle to allow one G3P to exit…. • Results in 5 molecules of GCP per every 3 turns to reform 3 molecules of RuBP…and the cycle continues. • The reaction uses some of the ATP produced from light reactions. Importance of the Calvin cycle • _____ is a product of the Calvin cycle – it can be converted to other molecules the plant needs • ____________________ is among the organic molecules that result from GCP metabolism • This is of interest because glucose is “the” molecule that plants and animals most often _____________ to produce ATP molecules required to meet their energy needs. • Examine next slide to see the _______ of G3P. Fate of G3P Glucose phosphate Fatty acid synthesis Amino acid synthesis Starch (in roots and seeds) Cellulose (in trunks, roots and branches) + Fructose phosphate + Sucrose (in leaves, fruits and seeds)