... The human body temperature is 37C, and without catalysts the reactions would be too slow to sustain life. Since there are thousands of different reactions happening in cells, and each requires a specific enzyme, enzymes must be made of a type of chemical which can vary enormously in structure, amino acids. There are roughly 20 different amino acids, which can be linked in infinite amount of ways. This means that the primary and tertiary structure of enzymes can show the variability needed to achieve specificity, particularly upon the shape of a small part of the enzyme molecule where the enzymes actually come in contact with the substrate molecule, the active site. This is a small 'cleft' on the enzyme surface, where certain amino acid residues are exposed. The substrate molecule fits into the active site and interacts with these amino acids by ionic and hydrogen bonding, forming and enzyme-substrate ...

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