Most ATP in both bacteria and in
higher life is generated by a proton gradient. An electron donor, donates an electron to a
series of carriers imbedded in a membrane. As electrons are transferred from donors to
acceptors, the energy release is used to pump hydrogen atoms across the membrane, figure
14.6. Another very complex enzyme called ATP synthase then uses this proton gradient to
create ATP from ADP. Because it is found in all living things, ATP synthase must have
evolved very early in the evolutionary process.
Figure 14.6 Electron Transfer Drives a Proton Pump
Many authors have suggested that one of the various bacteria that
consume hydrogen, methane, iron or sulfur were probably one of the first forms of life,
but these metabolic pathways are very complex and contain too much information to be the
first route to synthesize ATP. They all use ATP synthase in combination with the proton
pump shown in figure 14.6 to generate ATP. Furthermore, ATP synthase is one of the most
complex proteins found in life. There must be a simpler solution.
A class of enzymes called dehydrogenases facilitate oxidation and in
many cases, capture the energy released. In figure 14.6, the dehydrogenase serves as a
hydrogen pump, but many dehydrogenase enzymes are capable of directly creating high energy
phosphate bonds. Today, no dehydrogenase creates ATP directly from oxidation, but in
theory, there is no reason that one could not have in the distant past. This path seems
much more promising for origin of life theories because it would only require a single
enzyme. The next section will explore this idea.
next: ATP
synthesis
home: Intelligent Design and the origin of life
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