In multistep reaction pathways, what can be said about some steps in terms of ΔG?

In multistep reaction pathways, it is indeed possible for some steps to have a positive ΔG. This reflects the fact that not every individual reaction or step within a pathway will be energetically favorable. Each step can have varying ΔG values depending on the specific reactants, products, and the conditions under which they occur.

A positive ΔG indicates that a step is not thermodynamically favorable in the direction that the reaction is proceeding, meaning that energy must be input for the reaction to occur. However, these steps can still be part of the overall pathway due to the coupling of reactions or the influence of other factors, such as concentrations of substrates and products, or even the energy released by subsequent steps that may have large negative ΔG values.

In a multistep process, the overall change in free energy (ΔG of the entire pathway) can still be negative, making the overall reaction spontaneous, even if some intermediate steps are non-spontaneous. Thus, recognizing that some steps can indeed have a positive ΔG is key in understanding these pathways in biochemistry.