lecture21 - LECTURE 21 14 October 2009(P J Hollenbeck...

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-1- LECTURE 21 14 October 2009 (P. J. Hollenbeck) BIOL231 Plant Photosynthesis Read pp. 478-86; DVD 14.6, 147 Probs: exam II ‘05, #1; ECB Q14-16 &17 <Overview> Living cells require a continuous input of energy. As you know, this is because living systems continually consume energy that is "spent" in constructing, maintaining and organizing the cell (overcoming entropy). The input of energy comes from our star, the sun, and is converted into useful chemical energy by photosynthesis. Although we will focus on photosynthesis in plant cells, much of what we know about the detailed structure of the machinery comes from studies of photosynthetic bacteria.> Recall that the breakdown of sugar through glycolysis, the TCA cycle, electron transport and ATP 22 2 synthesis gives: glucose + O ==> CO + H O + ATP Photosynthesis is essentially the opposite: 2 2 2 CO + H O + solar energy ==> glucose + O As cell biologists, we want to understand photosynthesis at two levels: (i) be able to compare and contrast the organization of the mitochondrion and the chloroplast, recognizing where key reactions occur and how compartment boundaries are important in segregating reactions; (ii) be able to understand the overall schemes of glucose metabolism and glucose synthesis. I. Structure and function of the chloroplast [see fig. below and 14-25 thru -27 in ECB ] (A) Origin & organization of compartments (1) Although we will concentrate on the organization of photosynthesis in plant cells, remember that simpler and more “ingenious” systems of photosynthesis exist in bacteria, and these pre-date the evolution of plants, as we discussed in the last lecture. (2) The chloroplast, like the mitochondrion, seems likely to have its origin in endosymbiosis between an early eukaryotic cell and a procaryote: in this case, a photosynthetic bacterium similar to modern cyanobacteria. (3) Chloroplasts have an outer envelope comprised of two separate membranes with very little space in between: the outer envelope membrane , which has porins and is leaky like the outer mitochondrial membrane; and the inner envelope membrane , which is impermeable and contains a variety of transporters, similar to the inner mitochondrial membrane. (4) Within the envelope is a third, internal, membrane system called the thylakoid membrane that encloses an elaborately shaped compartment. The compartment has the form of many membranous sacs called thylakoids that are organized in many places into stacks called grana . Although the geometry looks complex, the lumens of these sacs and their stacks are all continuous with each other, forming a single innermost compartment called the thylakoid lumen . The space between the thylakoid membrane and the chloroplast envelope is called the stroma .
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-2- Fig 14-27 from ECB , comparing the structure of mitochondria and chloroplasts.
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lecture21 - LECTURE 21 14 October 2009(P J Hollenbeck...

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