Enzymes, commonly as known biocatalysts, are unique and highly specific proteinaceous substances (globular proteins).
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They are produced by the cell and have enarmous ability to catalyze virtually all of the chemical reactions or activities of living system in a highly and very effective manner.
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They are involved in such biological processes as digestion, respiration, the stepwise breaking down, building up and interconversion of carbohydrates, fats, proteins and nucleic acids, and the release and utilization of energy by living cells.
Enzymes greatly accelerate chemical reactions without themselves undergoing any apparent change in the process of work, Another distinguished feature of them is enormity of reactive power. e.g., mere trace of particular enzyme may induce quite a tremendous amount of chemical reaction.
Enzymes are universally present in living organisms, and the occurrence of metabolic reactions common to all cells reflects the specificity of the responsible enzymes.
The great stereo chemical specificity of enzymes results from complementarily of the conformation at the active side of the protein molecule with the geometry of the substrate.
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Enzymes are produced within the cells but capable of action outside the cells. Each cell probably contains hundreds of different enzymes.
Each enzyme usually acts on a single substance (substrate) or on a group of closely related substances. Enzymes which act on a particular substrate are said to be highly specific in their action.
The catalytic efficiency of enzymes is extremely high. Pure enzymes may catalyze the transformations of as many as 10,000 to 1,000,000 miles of substrate per min per mole of enzyme.
A considerable number of evidences suggest that enzyme and substrate combine transiently to form an enzyme-substrate complex.
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The enzyme and substrate are probably not coyalently linked but rather are held together by Van Der Waals interactions. The enzyme-substate complex dissociates into enzyme and products of the reactions.
Many enzyme-catalyzed chemical reactions require the presence of low molecular weight organic compounds called coenzymes.
These coenzymes act as donors or recipients of hydrogen atoms or other groups, and like enzymes, function over and over again.
Many enzymes require metal ions for their activation. In some instances these activators function in combination with the protein, in others, the metal ions forms a compound with the substrate, and it is the metal-substrate complex that reacts with the enzyme.
The ions of Ca, Co, Cu, Mg, Mn, Mo, Na, K and Zn are known to participate in enzymic reactions.
Enzymes are organized both functionally and structurally into groups which carryout sequences of chemical reactions.
The sequences of chemical reactions constitute the metabolic path ways. All of the enzymes in a metabolic pathway tend to be found in one type of intracellular organelle or in solution in the cell sap.
The destructive or catabolic pathways usually are downhill reactions, while the constructive or biosynthetic or anabolic pathways usually are uphill reactions which must be coupled to energy-releasing processes.