3500Ch21 - Essentially all free energy used by biological...

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2/4/11 Essentially all free energy used by biological systems is from Photosynthesis is the process that traps solar energy. CO2 + H2O (CH2O) + O2 Formation of carbohydrates – primarily sucrose and starch. This happens in chloroplasts. Chlorophylls, capture the energy of light and generate high-energy light
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2/4/11 22 Photosynthesis: Occurs in chloroplasts granum
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2/4/11 Chloroplasts Typically 5 microm long. Leaf cells contain between 1-100, depending on the species, cell type, and growth conditions. 3 membranes Outer, Inner and Thylakoid membranes
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2/4/11 Chloroplast from spinach leaf –
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2/4/11 Thylakoid membranes This is where things happen! 50-50 lipids - proteins Are impermeable to most molecules and ions (as is the inner membrane) Contains Light-harvesting proteins Reaction centers Electron-transport chain proteins, ATP synthase
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2/4/11 Chloroplasts Have DNA, and the machinery to replicate and express protein. Like mitochondria they are not autonomous Plants are dependent on chloroplasts and Cyanobacteria – the hypothesized ancestor of chloroplasts
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2/4/11 Electrons Used to produce NADPH ATP They are used to reduce CO2 creating 3- phosphoglycer ate (Calvin cycle, Ch 22, Light is used to remove electrons from water creating O2. These electrons reduce NADP+ to NADPH.
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2/4/11 Light absorption by chlorophyll – Substituted tetrapyrrole Coordinated to a central Mg ion. It is differentiated from heme, which binds Fe Effective photoreceptors because of the extensive network of alternating single and double bonds.
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2/4/11 Chlorophyll – Similar to heme, Mg binds at the center of the structure.
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2/4/11 Absorption spectrum of chlorophyll a and b
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2/4/11 What happens when the lights are on? Light excites an electron from the ground energy level to an excited energy level Sometimes the electron returns to the ground state and the energy is converted to heat. In the presence of an electron acceptor,
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3500Ch21 - Essentially all free energy used by biological...

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