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What has been described above are the noncyclic energy

What has been described above are the noncyclic energy -...

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What has been described above are the  noncyclic energy-fixing reactions  (see Figure  1  ). Certain  plants are also known to participate in  cyclic energy-fixing reactions . These reactions involve only  photosystem I and the P700 reaction center. Excited electrons leave the reaction center, pass  through coenzymes of the electron transport system, and then follow a special pathway back to  P700. Each electron powers the proton pump and encourages the transport of a proton across the  thylakoid membrane. This process  enriches the proton gradient and eventually leads to the  generation of ATP.  ATP production in the energy-fixing reactions of photosynthesis occurs by the process of  chemiosmosis . Essentially, this process consists of a rush of protons across a membrane (the 
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Unformatted text preview: thylakoid membrane, in this case), accompanied by the synthesis of ATP molecules. Biochemists have calculated that the proton concentration on one side of the thylakoid is 10,000 times that on the opposite side of the membrane. In photosynthesis, the protons pass back across the membranes through channels lying alongside sites where enzymes are located. As the protons pass through the channels, the energy of the protons is released to form high-energy ATP bonds. ATP is formed in the energy-fixing reactions along with the NADPH formed in the main reactions. Both ATP and NADPH provide the energy necessary for the synthesis of carbohydrates that occurs in the second major set of events in photosynthesis....
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