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Index >> Regulation of Protein Synthesis - Operon >> Structural Genes

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Regulation of Protein Synthesis - Operon Structural Genes Operator Genes Promoter Gene Regulator Gene Control Mechanism - Induction Control Mechanism - Repression Inducible System Repressible System Negative Control of Protein Synthesis Positive Control of Protein Synthesis Mutation in the Operon

Structural Genes

	Structural Genes - The structural genes direct synthesis of cellular proteins through messenger RNA (mRNA) and determine the sequence of amino acids in the proteins synthesized. There are as many structural genes in an operon as there are proteins or polypeptides under common control. Each structural gene may be controlled independently and transcribe a separate mRNA molecule, or all the structural genes of an operon may form one long polycistronic or polygenic mRNA molecule.
Polygenic mRNAs are common in bacteria and bacteriophages. All known eukaryotes, however, contain only a single functional site for initiating protein synthesis The lactose (lac) operon of the bacterium Escherichia coli has been particularly well studied. It is a small segment of a circular DNA molecule which constitutes most of the genetic material of the bacterium. It has three structural genes, z, y and a, which transcribe one long polycistronic mRNA molecule.
This controls the synthesis of three different proteins (enzymes), β-galactosidase, galactoside permease and galactoside transacetylase. These consist of 4, 1 and 2 units, respectively. β-galactosidase is the enzyme that splits lactose into glucose and galactose. Galactoside permease facilitates the entry of lactose into tbe cell. Galactoside acetylase appears in small quantities upon lactose induction
The initiation codon of structural gene z is TAC (corresponding to AUG of mRNA). It is located 10 base pairs away from the end of tbe operator gene. In the bacterium Salmonella typhimurium the histidine operon (histidon) has 10 structural genes.

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Regulation of Gene Activity in Eukaryotes Frenster's Model of Gene Regulation Nonhistone Protein as Derepressors Britten Davidson Operon Operator Model Sensor Genes Producer Genes Integrator Genes Receptor Genes

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