Enzymes and Metabolism - An Overview

Catalytic PowerWithout enzymes, metabolic reactions could not continue at a rate high enough to support any living processes. Enzymes increase reaction rates by a 10(7) times. That is 10 million times faster. In fact, in many enzyme-controlled reactions the limit to the reaction rate is set by how fast the substrate molecule collides with the active sites.The power of enzymes must be controlled, as the product of any enzyme-controlled reaction is needed in very specific amounts by the organism. Uncontrolled enzyme activity is just as dangerous to an organism as a lack of enzymes. An example of this is seen in the disease multiple sclerosis. The immune system of sufferers of this diseases wrongly sets destructive enzymes against parts of nerve cells. This results in nervous system breakdown leading to a number of symptoms, including paralysis.Control of metabolic sequencesMany metabolic processes involve a series of enzyme-controlled reactions. The processes of respiration and photosynthesis are examples of complex metabolic sequences. In these metabolic processes, the prodcut of one enzyme-controlled reaction is the substrate for next enzyme-controlled reaction in the sequence. Such chains of enzyme reactions are often called metabolic pathways.In controlling metabolic processes, it is vital to the organism that the end product of the sequence does not build up if it is not required. In many cases, the end product can attach to one of the enzymes early in the sequence. This is exacly the same as the reversible non-competitive inhibition.The end product binds to the enzyme in a part of the enzyme molecule away from the active site. Binding of the end product molecule changesthe shape of the active site, so it reduces the reaction rate of the enzyme.Some enzymes are crucial to lifeSome enzymes are found in all organisms, so they appear to be vital for life itself. The enzyme ATP synthase, catalyses the addition of an inorganic phosphate group to an ADP molecule - creating ATP. ATP synthase is found in the cells of all organisms, from bacteria to flowering plants and humans. The ATP generated in this reaction acts as a short-term energy supply in cells.Inborn errors of metabolismAll enzymes are proteins. As with all proteins, any organism must have the instructions to make the enzymes it needs in the form of DNA. If the DNA forming the instructions for an enzyme is faulty, then the enzyme may not be made correctly. Many diseases are caused by the lack of a functioning specific enzyme in a metabolic sequence. These are called inborn errors of metabolism.The condition phenylketonuria is an inborn error of metabolism. Individuals with this condition lack a functioning version of the enzyme phenylaline hydroxylase, which breaks down excess phenylaline builds up and in young individuals, causes irreversible damage to the nervous system and to brain development. Affected individuals must have a diet with very little phenylalanine.

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