. Biophysical science. Biophysics. 20 : 3/ Photosynthesis 367 then the ADP available will increase, thereby speeding up the rate of phosphorylation. Likewise, if phosphorylation proceeds more rapidly for a time, then the ADP supply will be depleted and the rate of phos- phorylation decreased. This is a simple example of the action of nega- tive feedback on a chemical scale serving to keep the two processes in step. Input Output. One 02 liberated per CO 2 used Net Loss: One H20 per C02 used Net Gain: One hexose per 6 C02 used Figure 3. Block diagram of reactions within chloroplast. The brackets
. Biophysical science. Biophysics. 20 : 3/ Photosynthesis 367 then the ADP available will increase, thereby speeding up the rate of phosphorylation. Likewise, if phosphorylation proceeds more rapidly for a time, then the ADP supply will be depleted and the rate of phos- phorylation decreased. This is a simple example of the action of nega- tive feedback on a chemical scale serving to keep the two processes in step. Input Output. One 02 liberated per CO 2 used Net Loss: One H20 per C02 used Net Gain: One hexose per 6 C02 used Figure 3. Block diagram of reactions within chloroplast. The brackets around the H and O indicate that these do not imply molecular or atomic hydrogen and oxygen, but rather reducing and oxidizing compounds. Considerable evidence indicates there is a flavin mononucleotide intermediate between (H) and pyridine nucleotide. The circle for the carbon pathways and the square for the phosphorylating chain are purely diagram- matic. The carbon pathway is discussed in more detail in Section 4. There is not an instantaneous balance between C02 fixed and 02 released. A feedback mechanism, con- trolling the rate of phosphorylation, assures that over a period of time the number of moles of 02 released is equal to the number of moles of G02 fixed. One may then summarize the action of the chloroplast schematically as shown in Figure 3. This shows H20, C02, and photons being used up, and H20, 02, and hexose being formed. It emphasizes the three types of reactions catalyzed by the chloroplasts, the splitting of water, the fixation of carbon dioxide, and photosynthetic Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ackerman, Eugene, 1920-. Englewood Cliffs, N. J. , Prentice-Hall
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