How does the kalvin cycle work? Solution The Calvin Cycle The Calvin cycle is a

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The Calvin Cycle The Calvin cycle is a metabolic pathway found in the stroma of the chloroplast in which carbon enters in the form of CO2 and leaves in the form of sugar The cycle spends ATP as an energy source and consumes NADPH2 as reducing power for adding high energy electrons to make the sugar. There are three phases of the cycle. In phase 1 (Carbon Fixation), CO2 is incorporated into a five-carbon sugar named ribulose bisphosphate (RuBP). The enzyme which catalyzes this first step is RuBP carboxylase or rubisco. It is the most abundant protein in chloroplasts and probably the most abundant protein on Earth. The product of the reaction is a six-carbon intermediate which immediately splits in half to form two molecules of 3-phosphoglycerate. In phase 2 ( Reduction), ATP and NADPH2 from the light reactions are used to convert 3-phosphoglycerate to glyceraldehyde 3-phosphate, the three-carbon carbohydrate precursor to glucose and other sugars. In phase 3 (Regeneration), more ATP is used to convert some of the of the pool of glyceraldehyde 3-phosphate back to RuBP, the acceptor for CO2, thereby completing the cycle. For every three molecules of CO2 that enter the cycle, the net output is one molecule of glyceraldehyde 3-phosphate (G3P). For each G3P synthesized, the cycle spends nine molecules of ATP and six molecules of NADPH2. The light reactions sustain the Calvin cycle by regenerating the ATP and NADPH2. Calvin Cycle The following formula summarizes the Calvin cycle. C5 + CO2 + ATP + NADPH ---> C6H12O6 where C5 is a fivecarbon molecule, such as pyruvate, when is recycled as glucose is synthesized. The Calvin cycle is the last step in photosynthesis. The purpose of the Calvin Cycle is to take the energy from photosystem I and fix carbon. Carbon fixation means building organic molecules by adding carbon onto a chain. In order to do this, you have to start with an organic molecule, a starter molecule. In this case, the starter molecule is a 5-chain carbon compound (C5). I'll skip the names of most of the organic molecules in this process. We'll cover it in AP Biology. The first step in the Calvin cycle is for the 3C5 to bind with 3CO2, producing a six 3-carbon organic molecules (6C3). Next, 6ATP and 6NADPH energizes the binding of a C3 to make a 6-carbon molecule (C6), glucose. The remaining 5C3 continues moving through the Calvin cycle, being turned back into the starter C5 organic molecule. There is also some very helpful diagrams on these websites... http://library.thinkquest.org/C004535/media/calvin_cycle.gif http://www.starsandseas.com/SAS_Images/SAS_Cell_Images/SAS_organelles/calvin%20cycle.jpg Also, if you type in Calvin Cycle in Google Images, several other helpful diagrams will come up. I find it much easier to learn from the diagrams than from a word for word description.

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