![Most enzymes are proteins. Enzymes regulate nearly all chemical reactions that occur in living …[Credits : Acquired from Vast Video]](http://media-2.web.britannica.com/eb-media/56/86856-003-B3DD97D8.gif)
a substance that acts as a catalyst in living organisms, regulating the rate at which chemical reactions proceed without itself being altered in the process.
A brief treatment of enzymes follows. For full treatment, see protein: Enzymes.
The biological processes that occur within all living organisms are chemical reactions, and most are regulated by enzymes. Without enzymes, many of these reactions would not take place at a perceptible rate. Enzymes catalyze all aspects of cell metabolism. This includes the digestion of food, in which large nutrient molecules (such as proteins, carbohydrates, and fats) are broken down into smaller molecules; the conservation and transformation of chemical energy; and the construction of cellular macromolecules from smaller precursors. Many inherited human diseases, such as albinism, result from a deficiency of a particular enzyme.
Enzymes also have valuable industrial and medical applications. The fermenting of wine, leavening of bread, curdling of cheese, and brewing of beer have been practiced from earliest times, but not until the 19th century were these reactions understood to be the result of the catalytic activity of enzymes. Since then, enzymes have assumed an increasing importance in industrial processes that involve organic chemical reactions. The uses of enzymes in medicine include killing disease-causing microorganisms, promoting wound healing, and diagnosing certain diseases.
All enzymes were once thought to be proteins, but since the 1980s the catalytic ability of certain nucleic acids, called messenger RNAs, has been demonstrated, refuting this axiom. Because so little is yet known about the enzymatic functioning of RNA, this discussion will focus primarily on protein enzymes.
A large protein enzyme molecule is composed of one or more amino acid chains called polypeptide chains. The amino acid sequence determines the characteristic folding patterns of the protein’s structure, which is essential to enzyme specificity. If the enzyme is subjected to changes, such as fluctuations in temperature or pH, the protein structure may lose its integrity (denature) and its enzymatic ability. Denaturation is sometimes, but not always, reversible.
Bound to some enzymes is an additional chemical component called a cofactor, which is a direct participant in the catalytic event and thus is required for enzymatic activity. A cofactor may be either a coenzyme—an organic molecule, such as a vitamin—or an inorganic metal ion; some enzymes require both. A cofactor may be either tightly or loosely bound to the enzyme. If tightly connected, the cofactor is referred to as a prosthetic group.
Curves-representing-enzyme-actionFigure 9: Curves representing enzyme action (see text).
Mechanisms-of-enzymatic-actionFigure 8: Mechanisms of enzymatic action (see text).
Induced-fit-binding-of-a-substrate-to-an-enzyme-surfaceFigure 10: Induced-fit binding of a substrate to an enzyme surface and allosteric effects (see …
The-role-of-the-active-site-in-the-lock-andFigure 7: The role of the active site in the lock-and-key fit of a substrate (the key) to an enzyme …
Most enzymes are proteins. Enzymes regulate nearly all chemical reactions that occur in living …[Credits : Acquired from Vast Video]
Competitive inhibitors prevent enzymes from catalyzing with substrates.[Credits : Acquired from Vast Video]
An environment that is neither acidic nor alkaline is best for most enzymes in the human body. …[Credits : Acquired from Vast Video]
Any disruption of an enzyme’s pathway can affect the body in ways which can be life threatening.[Credits : Acquired from Vast Video]
A molecule which interacts with an enzyme in order for it to react with a substrate is called a …[Credits : Acquired from Vast Video]
Some noncompetitive inhibitors use a process called negative feedback to regulate how efficiently …[Credits : Acquired from Vast Video]
The dangers posed by the ingestion of lead paint are a good example of how noncompetitive …[Credits : Acquired from Vast Video]
The breakdown of glucose helps generate ATP, a major source of energy.[Credits : Acquired from Vast Video]
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