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Introduction |
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Genes do not operate to produce enzymes all the time. Each gene is normally more or less repressed (inactive); but, when a particular enzyme is needed, the relevant gene becomes active to bring about the production of that enzyme. A totally active gene can produce a very large amount of enzyme. If the synthesis of all the enzymes is fully accelerated in a cell, it would enter into a metabolic chaos. |
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Gene Regulation in Prokaryotes |
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Bacteria cells can regulate the synthesis of enzymes in such a way that the enzymes are produced only when the substrates which these enzyme utilise are present in the cell. |
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Inducible Operon |
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This is a type of operon which is switched on when a chemical, called inducer, is present. The inducer is almost always a substrate. This operon has following components. |
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Repressible Operon |
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Another type of operon system is the repressible operon which is regulated by a chemical substance called co-repressor. It is almost always the end product of a metabolic reaction. The operon is switched off when the co-repressor, is present. |
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Gene Regulation in Eukaryotes |
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In eukaryotes, the genes that code for the enzymes needed to catalyse the various steps of a particular metabolic pathway may not be adjacent or even be in different chromosomes. However, these genes are regulated by operon model as in bacteria. Both the inducible and the repressible systems of the operon model work in the eukaryotic cells but through a complex network of regulatory genes. |
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Advantage of the Regulation of Gene Action |
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An operon is the unit of transcription. When excess protein is present, it is no longer economical for the cell to use up its energy and materials in the synthesis of enzymes that are not immediately needed. Hence, the protein synthesis is stopped. This is clearly advantageous for the cell. |
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House Keeping Genes |
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All the genes do not play the same role, nor are all the genes active all the time. With regard to their role and activity, the genes are of two different types. |
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Summary |
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Inducible operon system consists of structural genes (cistrons), operator gene can either switch on or switch off the structural genes by allowing or not allowing RNA polymerase molecules found attached to promoter gene. |
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