Because non-biological catalysts are often very small compounds, it is reasonable to wonder why biological catalysts, namely, enzymes, are so large. With the possible exception of enzymes that are secreted by cells, most of a cell's enzymes are either permanently or cyclically associated with membranes and other particulate cell components. Indeed, in a few cells (e.g., Euglena and Neurospora), there [...]
The interaction between the substrate and the enzyme takes place in a particular region of the enzyme molecule called the active site. In many instances compounds other than the normal substrate for a particular enzyme-catalyzed reaction may bind to the enzyme's active site, and this has a significant effect on the kinetics of the normal reaction. One possible consequence of [...]
When enzymes contain more than one active site, the binding of a substrate molecule to the first site may influence substrate binding to a second site. Binding of the second substrate may influence binding of a third, and so on. This phenomenon is called cooperativity. The influence may be positive in that binding of the first substrate molecule facilitates binding [...]