Many processes in cells are energetically unfavorable (AG > 0) and will not proceed spontaneously. Examples include the synthesis of DNA from nucleotides and transport of a substance across the plasma membrane from a lower to a higher concentration. Cells can carry out an energy-requiring reaction (AG1 > 0) by coupling it to an energy-releasing reaction (AG2 < 0) if the sum of the two reactions has a net negative AG.
Suppose, for example, that the reaction A B + X has a AG of +5 kcal/mol and that the reaction X ^^ Y + Z has a AG of -10 kcal/mol.
In the absence of the second reaction, there would be much more A than B at equilibrium. However, because the conversion of X to Y + Z is such a favorable reaction, it will pull the first process toward the formation of B and the consumption of A. Energetically unfavorable reactions in cells often are coupled to the hydrolysis of ATP, as we discuss next.
Was this article helpful?
Discover secrets, myths, truths, lies and strategies for dealing effectively with cholesterol, now and forever! Uncover techniques, remedies and alternative for lowering your cholesterol quickly and significantly in just ONE MONTH! Find insights into the screenings, meanings and numbers involved in lowering cholesterol and the implications, consideration it has for your lifestyle and future!