Question

6. Explain how reaction coupling can be used to drive unfavorable processes in metabolic pathways. 7. Define the term metabolic flux. 8. List the mechanisms by which pathways are regulated/controlled. 9. Distinguish between kinetic control and thermodynamic control of a reaction. 10. Distinguish between AG, AG”, AG’ and AG°'. 11. Calculate any AG as above for an overall reaction. 12. Review and interpret velocity vs. [S] curves that are hyperbolic vs. sigmoidal.

Answer 1

6. ATP energy in anabolism is used to drive energetically unfavorable reactions by coupling the hydrolysis of ATP (an energetically favorable process) with the reaction that is energetically unfavored (such as the addition of phosphate to glucose). By doing this coupling, an unfavorable reaction becomes energetically favorable. Thus, the synthesis of large molecules from small ones is not energetically favorable, but when energy from ATP is provided, they become energetically favorable.
7.Metabolic flux is the rate of turnover of molecules through a metabolic pathway. flux is regulated by the enzymes involved in a pathway. Within cells, regulation of flux is vital for all metabolic pathways to regulate the pathway's activity under different conditions.
8.metabolic pathways are often regulated by feedback inhibition. Some metabolic pathways flow in a 'cycle' wherein each component of the cycle is a substrate for the subsequent reaction in the cycle, such as in the Krebs Cycle .
9. In general, short reaction times favour kinetic control whereas longer reaction times favour thermodynamics control. In the same manner, if a reaction is under kinetic control at a given temperature, it will also be under kinetic control at any lower temperature for the same reaction time.