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Figure 1. The Chemiosmotic Paradigm. The two basic energy sources
in living systems--respiration and light--lead to the generation of a proton
electrochemical gradient ( Since protons (i.e., hydrogen ions or H+) are being pumped vectorally by either the respiratory chain or the photosynthetic electron transfer chain, positive charge is being pumped, and an electrical potential (DY) is generated, the polarity of which depends upon which direction the protons are pumped (when protons are pumped out, DY is interior negative; when pumped in, DY is interior positive). In addition to DY, a chemical concentration gradient of protons (DpH) may also be established, the polarity of which is also dependent upon the vectorality of the proton pump (when protons are pumped out, DpH is interior alkaline; when pumped in, DpH is interior acid). Don’t worry about the constants (R, T and F) which are there simply to put both components into the same units [in this case, millivolts (mV)]. The important take-home message is that electrochemical proton gradient means just what it says; there are two components, DY and DpH, that are important energetically. |