Metabolism: Part 3

An enzyme is a protein that serves as a biological catalyst. A catalyst is a substance that accelerates a chemical reaction without actually being a reactant in that reaction. In other words, a catalyst (and therefore an enzyme) does not get changed into another substance (a product). An enzyme interacts with reactants in such a way as to make it much more likely for those reactants to chemically react, turning them into products.

We call the reactants of a catalyzed reaction substrates. An enzyme operates by temporarily binding to substrates. The rate of the reaction (its speed) when an enzyme catalyzes it is typically at least one million times the rate without the help of an enzyme. This is why enzymes are absolutely vital. Without enzymes, the biochemical reactions of metabolism would occur much too slowly to support life. Importantly, since an enzyme does not get altered in a reaction in which it participates, it is reusable, and it can continue to catalyze the same sort of reaction if more substrate is present.

Watch this video, which discusses the characteristics and functions of enzymes. The presenter describes various factors that promote and affect enzyme activity, such as temperature, pH, concentrations, competitive inhibition, and allosteric regulation. Pay attention to the discussion on feedback inhibition and the regulatory mechanisms of catabolic pathways. Think about how this type of regulation benefits cells in terms of energy conservation.

After watching this video, you should be able to describe how inhibitors regulate the activity of enzymes of metabolic pathways and explain how excess products inhibit pathways to prevent a cell from wasting chemical resources.