Chemically, enzymes are generally globular proteins. Enzymes are catalysts that breakdown or synthesize more complex chemical compounds. They speed up the rate of chemical reactions because they lower the energy of activation, the energy that must be supplied in order for molecules to react with one another. Anything that an enzyme normally combines with is called a substrate. Enzymes are very efficient. Enzymes are only present in small amounts in the cell since they are not altered during their reactions. and they are highly specific for their substrate. Each enzyme has an optimum temperature and pH at which it works best. However, at much higher temperature, they are denatured. Related Theory Enzymes speed up the rate of chemical reactions because they lower the energy of activation, the energy that must be supplied in order for molecules to react with one another. Enzymes lower the energy of activation by forming an enzyme-substrate complex allowing products of the enzyme reaction to be formed and released Caution Ribozyme is a form of ribosomal RNA (23 SrRNA) which acts as a catalyst in splicing of RNA during protein synthesis. It is the only non-protein enzyme known so far, rest all the ensymes are proteinaceous