What is the importance of enzymes for living beings?
Enzymes are proteins that are catalysts of chemical reactions. From Chemistry it is known that catalysts are non-consumable substances that reduce the activation energy necessary for a chemical reaction to occur. Enzymes are highly specific to the reactions they catalyze. They are of vital importance for life because most chemical reactions of the cells and tissues are catalyzed by enzymes. Without enzymatic action those reactions would not occur or would not happen in the required speed for the biological processes in which they participate.

What are the main theoretical models that try to explain the formation of the enzyme-substrate complex?
There are two main models that explain the formation of the enzyme-substrate complex: the lock and key model and the induced fit model. In the lock and key model the enzyme has a region with specific spatial conformation for the binding of the substrate. In the induced fit model the binding of the substrate induces a change in the spatial configuration of the enzyme for the substrate to fit.

What happens to a denatured enzyme regarding its functionality? How can that result be explained with the help of the lock and key model?
According to the lock and key model the enzyme functionality depends entirely on the integrity of the activation center, a molecular region with specific spatial characteristics. After the denaturation the spatial conformation of the protein is modified, the activation center is destroyed and the enzyme loses its catalytic activity.

What are the main theoretical models that try to explain the formation of the enzyme-substrate complex?
The main factors that change the speed of enzymatic reactions are temperature, pH and substrate concentration (quantity).

How does temperature affect the action of enzymes upon their substrates?
There are defined temperature ranges under which enzymes operate and there is a specific temperature level (optimum temperature) in which enzymes have maximum efficiency. Therefore temperature variations affect enzymatic activity and the speed of the reactions they catalyze. In addition, as proteins, enzymes can be denatured under extreme temperatures.

Does pH affect the enzyme activity?
The concentration of hydrogen ions in solution affects the enzyme activity. Each enzyme has maximal efficiency under an optimum pH. Since pH is one of the factors for the denaturation of proteins, if an enzyme is submitted to a pH level under which it is denatured there will be no enzymatic activity.

Do enzymes act better under acid or basic pH?
Most enzymes act in pH between 6 and 8, a range that corresponds to the general acidic level of cells and blood. There are enzymes, however, that act only under very acid or very basic pH. So enzyme activity depends on pH interval.