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| = The Lac Operon =
| | See [[Lac_operon|Lac Operon]] |
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| == What is the Lac operon? ==
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| The lac operon is a good example of how genes are regulated. The lac operon was studied in E.coli.(1) It contains 3 genes that are needed to produce proteins that are required to break down lactose when it is present in the cell. These 3 genes are Lac Z, Lac Y and Lac A. Each code for B- galactosidase, Permease and Transacetylase respectively. (2)
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| Further up the genetic code from these three genes, upstream, lies the promoter sequence. RNA polymerase needs a region in which it can join the genetic code, the promoter sequence, before it can start transcribing. RNA polymerase is required in transcription of the Lac operon. (3) [[Image:Lac_operon_-_basic.JPG]]<br>
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| == When does the Lac operon function?<br> ==
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| The Lac operon does not function all the time and so has to be regulated. When lactose is present in the cell and glucose is absent, then the Lac operon is active and the 3 genes are transcribed to break down this lactose in the cell.
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| == Negative gene regulation ==
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| The conditions inside the cell are changing all the time. So what happens when glucose is present and lactose levels are low? The Lac operon is no longer required to make the proteins to break down lactose and so its function is switched off. This is done by the use of a repressor protein. (4)<br>Upstream of the promoter sequence there is another gene. This is the Lac I gene. The Lac I gene is transcribed to make the repressor protein which binds to the operator sequence.<br><br>
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Latest revision as of 20:25, 3 January 2011