AP Biology 3.3 Cellular Energy- Exam Style questions - FRQ

Ans:

Chemiosmosis is the mechanism by which a hydrogen ion gradient is used to drive an energy-requiring process, like the synthesis of ATP.In mitochondria and chloroplasts, ATP synthase performs this function.Building a gradient requires energy. If the ultimate goal of chemiosmosis is the synthesis of ATP, the use of ATP to build the proton would, at best,result in no net ATP (and in reality, no energy transformations in the cell are
100% efficient, so you’re going to use more energy than you harness). The energy to drive the proton pumps is harnessed from the electrons delivered to the electron transport chain by NADH or \(FADH_2\) in the mitochondria and by an electron acceptor in photosystem II in the chloroplast.In the mitochondria, the movement of electrons from NADH and \(FADH_2\) to oxygen, creating water, has a (very) negative free energy
change; that is, it is exergonic, spontaneous, and downhill. The potential energy of the electrons is lowered, which means there was a conversion of potential energy to other forms of energy. The change in potential energy,from lower stability glucose to higher stability water, is what drives the protons against their concentration gradient. This is a coupled process. A downhill process can drive an uphill process if they are coupled. Every endergonic process has a price. See answer 124 for an explanation of how a proton gradient stores potential energy. The potential energy of the gradient is raised with each proton that enters the high concentration compartment and lowered with each proton that leaves. The spontaneous flow of hydrogen ions from high to low concentration drives the endergonic synthesis of ATP. The exergonic processes are the downhill, driving reactions. They spontaneously happen. The endergonic processes require work. The energy to do the work is harnessed from the reaction it is coupled with. Coupled processes occur concurrently in the same place. They are physically and temporally linked. The first two reactions occur at the cytochrome complexes. The oxidation-reduction reactions of the transport of the electrons down the chain provide the energy for proton translocation. The cytochrome complexes are multi-protein complexes composed of electron carriers and a proton pump. The second two processes are coupled through ATP synthase. The giant, multi subunit protein complex also translocates protons, but in the direction of their diffusion, harnessing the energy of their diffusion for the synthesis of ATP from ADP and \(P_i\).