Question

Apply the concept of the “conservation of energy” to central metabolism. Follow energy from “sources” of electrons with relatively low reduction potentials to “sinks” with higher redox potentials, describe the major transfers of energy and how this energy is “stored” at each stage.

Answer 1

In photosynthesis, water breaks to yield electrons, whereas, in respiration, NADH breaks to give electrons, in both the cases the energy released by the breakage of bonds allows the electron to be raised from low reduction potential compounds to high reduction potential compounds finally giving electron to final electron acceptors releasing the energy to form bonds. In Photosynthesis this molecule is NADP which forms NADPH and in respiration that is oxygen. Hence the energy is returned to new bonds. While energy is available in form of bonds, they are broken to get energy and stored in form of bonds in ATP, to drive metabolic processes; when energy is to be used to perform work, the energy stored in ATP is released by breaking the bonds between ADP and phosphate.