Pathways can be linear, cyclic, or branched. These reactions make large molecules from smaller ones. The compounds used in reactions must be in sufficient concentration to permit reactions, but low enough to prevent disruptive side reactions.
Most reactions are reversible.
The rate of the reaction in either direction depends upon the concentration of the reactants. There is no NET change in the concentration of products or reactants what a reaction is at equilibrium. Reactions that are not reversible-often involve regulatory enzymes. 1 enzyme for forward run. 1 enzyme for reverse run.