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【正文】 ssage and a structure known as a polysome forms. In this way a cell may rapidly make many proteins. Text pg 231 Control of Genes: The Operon Model The operon model of prokaryotic gene regulation was proposed by Fancois Jacob and Jacques Monod… Groups of genes coding for related proteins are arranged in units known as operons. An operon consists of an operator, promoter, regulator, and structural genes. The regulator gene codes for a repressor protein that binds to the operator, blocking the promoter and thus blocking transcription of the gene. If the repressor protein is removed, transcription may again occur. Such regulatory proteins recognize and bind to specific DNA sequences and can either turnon or turnoff genes Gene On Gene Off Repressor does not bind. RNA pol free to run along Gene Repressor is Active. RNA pol can not bind. Gene is OFF. Gene Regulation Transcriptional control According to the Central Dogma, all cells transcribe RNA from DNA, and translate proteins from mRNA. In Bacteria, control of protein synthesis is at the level of transcription. That is, mRNA is only transcribed when a protein is needed。 when a protein is NOT needed, the mRNA is not made. Because the enzyme, RNA polymerase, carries out transcription, bacteria have a number of ways to either help RNA polymerase or stop it from doing it39。s job. This is done by using regulatory proteins that bind to DNA near promoter regions. These regulatory proteins switch back and forth between active and inactive conformations (shapes). In the active shape, the regulatory proteins bind to DNA。 in the inactive shape, they cannot bind DNA.
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