【多选题】Why is the chemiosmotic mechanism for ATP synthesis called oxidative phosphorylation?
A.
The chemiosmotic generation of energy begins when the activated carriers NADH and FADH 2 donate their electrons to the electron-transport chain in the inner mitochondrial membrane, becoming oxidized to NAD + and FAD, respectively, in the process.
B.
The electrons are quickly passed along the chain to molecular oxygen (O 2 ) to form water (H 2 O). The stepwise movement of these electrons through the components of the electron-transport chain releases energy that can then be used to pump protons across the inner mitochondrial membrane .
C.
The resulting proton gradient, in turn, is used to drive the synthesis of ATP. The inner mitochondrial membrane thus serves as a device that converts the energy contained in the high-energy electrons of NADH (and FADH 2 ) into the phosphate bond of ATP molecules.
D.
This chemiosmotic mechanism for ATP synthesis is called oxidative phosphorylation because it involves both the consumption of O 2 and the addition of a phosphate group to ADP to form ATP.
【多选题】How did chemiosmotic processes evolve in stages?
A.
The first stage might have involved the evolution of an ATPase (pump) that pumped protons out of the cell using the energy of ATP hydrolysis. Such a proton pump could have been the ancestor of present-day ATP synthases.
B.
Stage 2 could have involved the evolution of a different proton pump, driven by an electron-transport chain. Indeed, some present-day bacteria that grow on formic acid use the small amount of redox energy derived from the transfer of electrons from formic acid to fumarate to pump H + .
C.
Stage 3 could then link these two systems together to generate an ATP synthase that uses the protons pumped by the electron-transport chain to synthesize ATP.
D.
An early cell with this final system would have had a large selective advantage over cells with neither of the systems or only one.