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Semester 2- Week 2

  1. Describe the overall structure of a chloroplast and where the two major steps of photosynthesis take places. Talk about the thylakoid and the stroma. Discuss the light reactions (Photosystems I and II, ATP synthase, the electron transport chain) and the Calvin Cycle.
    1. So in photosynthesis there are two reactions: the light-dependent and the light-independent. Light-dependent reactions occur in the the little stacks of thylakoids, in the chloroplasts, called the granum. In light-dependent reactions, energy from light excited electrons found in chlorophyll. Electrons are then taken to the electron transport chain and used to pump Photosystem II, which basically creates an builds up the proton gradient inside the thylakoid. The electrons that are now in Photosystem II are now replaced by the split of O2 into H+ ions. The the light energy drives the electron transport chain in photosystem I. Then these same electrons attach to NADP inside of the stroma, which then binds with H+ ion to turn NADP into NAPDH. After that pretty much all that happens is that the ions flow down the concentration gradient throughout ATP synthase and create a lot of ATP.

    2. Light- independent reactions are also commonly referred to as the Calvin Cycle. There are three stages of the Calvin Cycle: fixation, reduction, and regeneration. During the fixation stage, six 3-PGA molecules are formed by the split of 3 RuBP molecules and the addition of 3 C02 molecules. Through the addition of NADPH and ATP, six molecules of Glyceraldehyde 3- phosphate are created from the six 3-PGA molecules.During this process, one of the six G3P molecules leaves to go form glucose and is no longer a part of the cycle. The remaining G3P molecules turn back into RuBP when more ATP is added, and the cycle continues.
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