Polypeptide synthesis proceeds until ER signal ..
Exergonic and endergonic reactions differ in that
As Mitchell predicted (1-3), the mitochondrial, bacterial, and chloroplast membranes that couple ATP synthesis to electron transport are poorly permeable to protons, except when proton-linked processes, such as ATP formation, occur at high rates. Proton transport was shown to be linked to electron transportin mitochondria (4), chloroplasts (5), and bacteria (6). The measurements of the magnitudes oficross these membranes turned out to be difficult, but in most instances, values approaching 20 kJ mol-1 (Dp ~ 200 mV) have been measured during steady state, rapid electron transport. As predicted by Mitchell, lipophilic weak acids (eg, 2,4-dinitrophenol) could collapse the A^H-by shuttling protons across the membrane. ATP synthesis is also inhibited by these reagents, which are termed "uncouplers" because they uncouple electron flow and ATP synthesis.
through dehydration synthesis, and become a polypeptide, ..
You have frequently heard ATP referred to as the "universal energycurrency" of the cell, and this is true for all organisms. Why ATP ended upbeing such a pivotal coenzyme, and not GTP, UTP, etc., is probably just a matterof chance. The free energy of biological oxidation reactions can be stored inthe bonds of ATP (chemical energy). It's relatively easy to hydrolyzepyrophosphate linkages in ATP, with the result that a considerable amount offree energy is released (Go' = -30.5kJ/mol for ATP hydrolysis to ADP and Pi ).If this were released intothe cell as heat, it would serve no useful purpose as far as making anendergonic chemical reaction proceed, since there's no way for the cell totransduce heat energy into work. But, if two reactions are "coupled"such that the product of an endergonic reaction is the reactant of an exergonicone (and the magnitude of the free energy change of the exergonic one is greaterthan that of the endergonic) then the exergonic reaction pulls the endergonicone through an intermediate. In other words, for chemical energy to be socoupled, there must be an intermediate common to both reactions in the set.