6.1: Introduction

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All living organisms depend on enzymes to catalyze (speed up) chemical reactions. Without enzymes, reactions would not occur fast enough to support life. There are many types of enzymes, active in all types of cells. Each reaction uses a specific enzyme.

Most enzymes are proteins. The amino acid sequence determines the three dimensional shape of the enzyme. This shape is critical because it allows the enzyme to interact with its substrate molecule, the molecule that the enzyme works on. Enzyme action changes the substrate into a product(s). The enzyme itself remains unchanged in the reaction, it can be reused. Each enzyme works best at a specific temperature and pH. Most enzymes in the human body exhibit maximal activity at 37^oC and a pH around 7. Extremes in temperature and pH can change the shape of the enzyme rendering it inactive.

Enzyme Properties

Most enzymes are proteins.
Enzymes speed up, or catalyze, chemical reactions, often by many thousand- fold.
Enzymes are required in small amounts.
Many enzymes require assistants, called cofactors. Cofactors may be metal ions such as iron and zinc, or vitamins
Enzymes can be reused. They are unchanged by the reaction.
Enzymes are specific. The substrate is the substance that the enzyme works on. Each substrate is digested by a specific enzyme.
Enzymes are affected by pH (acidity) and temperature. The rate of the reaction is dependent on these two variables.
Enzymes exposed to extremes in temperature or pH become denatured (lose their three dimensional shape and their activity).