What are the main characteristics of Enzymes?

Enzymes are biological catalysts. They speed up reactions although they are not changed in the reaction. Enzymes are proteins, and therefore are folded chains of amino acids with a specific shape. This shape is determined by the sequence of amino acids held together by bonds, for example Hydrogen bonds. Enzymes speed up reactions by bringing reactants together and reducing the activation energy required to start the reaction (enzymatic reaction).

Enzymes are specific: they have a specific shape, therefore only a certain substrate will fit its active site. There are two theories of enzyme action: Lock and Key and Induced Fit.  The lock and key theory states that only a certain substrate will fit a certain active site, just like a key fits a lock. Induced Fit, likewise, states that enzymes wrap around substrates, attracted to each other by opposite charges, forming an enzyme substrate complex.