The findings of Jacob - Monod experiment
François Jacob was a French biologist who with Jacques Monod proposed the theory of genetic regulatory mechanism the early 1960s. This is saying that they theorized that the level and type of enzyme activity was controlled and regulated by genes to operate at different times, there must be external factors such as environmental changes or a change in the external conditions to trigger different responses from the cell.
Jacob and Monad as well as another scientist received a Nobel prize in medicine for their work on the Lac operon. An operon is a unit of genomic DNA containing a cluster of genes under control of a single regulatory signal, this is also known as a promoter.
Figure 1 – Jacob and Monad experimenting on their theory.
Research
Jacob and Monad decided to experiment on the theory and therefore they studied the prokaryote Escherichia coli. These bacteria only produce the enzyme Beta- galactosade to break down the carbohydrate lactose when it is around the bacteria. The enzyme converts the disaccharide molecule which is lactose into glucose and galactose.
Figure 2- Lactose into galactose and glucose (http://bcrc.bio.umass.edu/intro/manual/index.php/Gene_Regulation_I)
In this figure we can see how lactose is broken down into galactose and glucose with the beta galactosidase being the catalyst.
However Jacob and Monad looked more closely to see how the bacterium reacts when lactose was not present in the medium. Does it still produce the enzyme continuously or does it somehow stop?
The answer is that it does stop making the enzyme to break down glucose. This is done by the lactose repressor binding to the DNA site which prevents the transcription of the Beta- galactosade enzyme from being produced.
However if lactose is present in the environment, the repressor is prevented from binding to the DNA molecule and therefore the Beta- galactosade gene is expressed and the mRNA coding for...