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| Summary |
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 Protein synthesis is a controlled process in which a given protein is synthesised in the cell only when it is necessary. |
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 When a particular protein is to be synthesised the specific gene has to express and initiate transcription. |
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 The mechanism that stimulates the expression of certain genes and inhibits the others is called gene regulation. |
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 The mechanism of gene regulation has been extensively studied in bacterial cells. |
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 In 1961 two scientists Jacob and Monad proposed the operon concept to explain the mechanism of gene regulation. |
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 There are two types of operon systems inducible and repressible |
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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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 The role of the operator gene is decided by a repressor protein synthesised by the regulate gene. |
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 The repressor protein binds with the operate gene, RNA polymerase cannot be allowed and hence structural genes get switched off. |
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 The repressor protein is kept in an active state by the inducer which is usually the substrate molecule. |
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 The repressible operon has the same components as in inducible operon. |
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 The repressor is here activated by a chemical substance called co-repressor, which is usually the end product. |
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 In eukaryotes gene regulation involves both inducible and repressible operons. |
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 The genes that code for enzymes of a given metabolic pathway may be even found on different chromosomes. |
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 Some genes in eukaryotic genes are always in a state of expression since the products that they code are constantly required for the survival of the cell. Such genes are called constitutive genes or housekeeping genes. |
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