Lecture 38Outline of Last Lecture I. Oxidative Phosphorylation InhibitionII. Hibernation A. 2,4-DinitrophenolIII. Heterotrophs vs. Phototrophs Outline of Current Lecture I. Photosynthetic EnergyII. Light Energy into Chemical EnergyA. Three ConditionsIII. ChloroplastsIV. Absorbance SpectrumCurrent Lecture This lecture continues on with the topic of photosynthesis. Greater than 1017 kcal of free energy are stored by photosynthesis on Earth per year. This is the same as 68 billion barrels of oil. This energy also corresponds to the assimilation of 1010 tons of carbohydrates. The purpose of photosynthesis is to capture light energy. This light energy is then used for the reduction of carbon dioxide into carbohydrates. This can be seen by the following equation. 6CO2 + 6 H2O + light energy yields C6 H12 O6 + 6O2The equilibrium constant for this reaction is 10-496 at 27 degrees Celsius. This value means that energy must be put into this reaction in order to drive it forward. This reaction can also be thought of as the reversal of glycolysis and mitochondrial respiration. The next question is how does the light energy become chemical energy? This transduction depends upon three things.1. There must be sequential oxidation-reduction reactions that pass electrons from water to NADPH. 2. These reactions must be compartmentalized in the chloroplast.3. A proton gradient must be generated from the above.Photosynthesis takes place in the chloroplasts of plant cells. Chloroplasts are a type of organelle found in plant cells. A part of the chloroplast called the stroma can be thought of as the equivalent to the mitochondrial matrix. The compartmentalization take place in the form of discs called thylakoids. Light energy is absorbed during photosynthesis through the use of photosynthetic pigments. This pigments have conjugated double bond systems. These pigments include the well-known chlorophyll. When BCHM 307 1nd Editionlooking at the absorbance spectrum of different photosynthetic pigments, it can be seen that they absorb blue and red light. This is in the range of 400-500 and 600 respectively. Accessory pigments can absorb outside these numbers and effectively extend the action spectrum for photosynthesis. Green light, in the 500-600 range, is never absorbed. This is why chloroplasts appear green; it is the only color not
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