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hey! What do u wanna know about gene expression?? I need more precisions An operon is 1) mostly found in PROKARYOTES 2)like a specific toolbox of STRUCTURAL GENES. It often regroups* (see after) a set of genes involved in a same pathway, all under control of the SAME PROMOTER, wich allows the coordination of a group of genes. A promoter is a serie of locis located just before the transcription initiation site and recognized by the RNApolymerase to initiate transcription; in the Eukaryotes genome it consists in two consensus sequences. One is called the -35 box (because its located 35 nucleotides before the initiation site, called +1), the other one, located 10 nucleotides before the trancription initiation site, is called the TATA box, because its sequence is TATAAT. WHEN THE RNA POLYMERASE INITIATE THE TRANSCRIPTION ON AN OPERON PROMOTER, it produces a huge mRNA, called POLYCISTRONIC because regrouping several genes in one mRNA. The typical example is the lactose operon. I'll continue this post if u think it's usefull. Sorry for my english, not my fault, it's because i'm french.... lol
An operon is a structure that regulates gene expression by turning genes on or off, such as the LAC operon can prevent the expression of a gene that produces lactase. Basically how it works is that the gene has a site that the operon can attach to and thereby prevent the gene from being read. If the operon is activated, it has bonded with a signaling molecule such as a hormone, and is in the correct "shape" to attach itself to the gene. If the necessary hormone is not present, the operon is in the wrong "shape" and cannot attach to the gene.
Gene expression can be controlled by an operon (as I just mentioned) but can also be controlled by other factors. This is epigenetics. For example, genes are wrapped around proteins called histones which then form chromatin. One way a gene can be controlled is by how tightly wound its histones are. If the histones are very tightly wound, it is harder for the gene to be expressed so it is transcribed less often and produces less protein than if it is loosely wound. I hope this helps...