what controls the type of reaction that the enzymes can help speed up?
Enzymes help to speed up a reaction in a cell/chemical reaction by lowering the activation energy needed to produce a reaction each enzyme act with only one substance/substrate like a lock and key. This is what is meant that they are specific for one reaction. Things that can change or alter an enzymes productivity would be: temperature extremes out of it's optimum range, as well as changes in pH, chemical presence (toxins) amt of substrate or conc. of enzymes in a solution.