MadSci Network: Cell Biology |
Endergonic means that the process requires an input of energy to proceed. Let me interpret your question as what I think you are asking. Unfavorable, energy-requiring reactions can be driven forward by coupling them to a favorable one. In biochemistry, many such reactions are driven by breaking the reactive, unstable bonds of ATP, which has two phosphoanhydride bonds and one phosphate ester bond. Sometimes people call such bonds energy-containing, but that is technically incorrect. Many enzymes can transfer one of these bonds to their substrate (the reactant, the thing that is acted on by the enzyme), often through a very short-lived bond with the enzyme itself, which then transfers the bond to the substrate. The substrate then is in a position to go forward to the product, again with the help of the enzyme. The final result is what is called hydrolysis of ATP, since ultimately by the end of the whole reaction sequence the unstable bonds are transferred to water (hydrolysis = "cutting by water"). Often, the reaction is meant to connect two substrates together, with ATP being used up as just described. So: in endergonic reactions that put two substrates together, you need two binding sites for the substrates that will go to the product, and one binding site for ATP. You often need reactive groups on the enzyme itself to attack the ATP. All of this means that you have more than one site where action is taking place.
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