BIOL 1107 1nd Edition Lecture 18Outline of Last Lecture I. PhotosynthesisII. Chloroplasts and ChlorophyllIII. Cyclic vs. Noncyclic Electron flowOutline of Current Lecture I. Calvin cycleII. C4 PlantsIII. CAM PlantsCurrent LectureI. Calvin Cycle- Uses ATP and NADPH to convert carbon dioxide to sugar- Location: stroma- It is a metabolic pathway similar to Krebs cycle in that a starting material is regenerated after molecules enter and leave the cycle- Carbon enters the cycle in the form of CO2 & leaves in the form of sugar - Cycle spends ATP as an energy source and consumes NADPH as reducing power for adding high-energy electrons to make the sugar- Carbohydrate produced directly from the cycle is actually not glucose, but a 3-carbon sugar name G3P- G3P is a sugar—the same 3-carbon sugar formed in glycolysis by the splitting of glucoseThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.II. C4 Plants- so named because they preface the Calvin cycle w/ an alternate mode of carbon fixation that forms a 4-carbon compound as its first product- Examples: sugarcane and corn, members of the grass family- In C4 plants, there are two distinct types of photosynthetic cells: bundle-sheath cells and mesophyll cells- Bundle-sheath cells are arranged into tightly packed sheaths around the veins of the leaf- Between the bundle sheath and the leaf surface are the more loosely arranged mesophyll cells- First step is addition of CO2 to PEP to form the four-carbon product oxaloacetate- In effect, mesophyll cells of a C4 plant pump CO2 into bundle sheath, keepingthe CO2 concentration in bundle-sheath cells high enough for rubisco to accept carbon dioxide rather than oxygen- In this way, C4 photosynthesis minimizes photorespiration and enhances sugar production- This adaptation is especially advantages in hot regions w/ intense sunlight, and it is in such environments that C4 plants evolved and thrive todayIII. CAM Plants- Second photosynthetic adaptation to arid conditions has evolved succulent (water-storing) plants (including ice plants), many cacti, pineapples, and representative of several other plant families - At night, these plants open their pores (stomata)- During day, they close those stomata- So, how do light reactions occur in these plants?- During night, when their stomata are open, these plants take up CO2 and incorporate it into a variety of organic acids- This mode of carbon fixation is called CAM - The mesophyll cells of CAM plants store the organic acids they make during the night in their vacuoles until morning, when the stomata close- During the day, when the light reactions can supply ATP and NADPH for Calvincycle, CO2 is released from organic acids made the night before to become incorporated into sugar in the chloroplasts- CAM pathway is similar to C4 pathway in that carbon dioxide is first incorporated into organic intermediates before it enter Calvin cycle- The difference is that in C4 plants, the initial steps of carbon fixation are separated structurally from Calvin cycle, whereas in CAM plants, the two steps occur at separate
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