Control Mechanisms. -Lac operon - Trp operon. Introduction. While there are 42 000 genes coding for proteins in our bodies, some proteins are only needed at certain times. Our cells can actually control transcription and translation based on what we require and what we don’t.
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While there are 42 000 genes coding for proteins in our bodies, some proteins are only needed at certain times. Our cells can actually control transcription and translation based on what we require and what we don’t.
The genes that are absolutely necessary at all times are called house keeping genes. Transcription factors are proteins that are able to turn genes on. Gene regulation involves the control of turning gene’s on and off. The four levels of control are transcriptional, posttranscriptional, translational and posttranslational.
In prokaryotic cells, the promoter and the operator control the genes.The two operons that will be further explored are:- lacoperon- trpoperon
When you combine glucose and galactose, it forms a disaccharide called lactose. Lactose also helps in the growth of E-coli. In order for E-coli to make use of the energy, it splits lactose into two separate sugars. The enzyme that degrades lactose is beta-galactosidase. This enzyme is only used when necessary as it would be extremely costly to produce it for nothing.
There are three genes in the operon : lacZ , lacY and lacA. If there is no lactose, beta-galactase cannot be made as it is blocked by the negative control system. The gene for B-galactosidase can be found in the operon.
Without lactose, transcription and translation are blocked. Only if lactose is added can the roadblock be removed. This is why lactose is called a signal molecule or inducer.
Signal molecule: a molecule that activates an activator protein or represses a repressor protein.Inducer: a molecule that binds to a repressor protein and causes a change in conformation, resulting in the repressor protein falling off the operator.
Lactose binds to LacL and the lactose and LacL fall off the DNA and transcription continues.
E-coli produces proteins using tryptophan, which is an amino acid. It can be produced by the E-coli and they will only stop once they have too much. The amount of the tryptophan controls the repression of the trpoperon. The trpoperon is made up of five genes that code for 5 different polypeptides and produce three enzymes to synthesize tryptophan.
Di Giuseppe, Maurice, Vavitsas, A., Ritter, Dr. Bob, & F., Douglas (2003). Biology 12. Canada: Thomson Nelson.