Lac Operon Demonstration

These past few weeks in class, we have been learning about gene expression and how molecules work together to ensure that each cell expresses only the right genes. In bacteria, DNA contains a group of molecules called the operon that works to express genes only when necessary so that the cell can conserve energy.

The lac operon is one common example of an inducible operon, meaning that the gene is normally off and can be turned on by the presence of lactose molecules. The lac operon consists of a repressor gene that codes for repressor proteins, the promoter where RNA polymerase binds to, the operator where repressor proteins bind to, and the genes of interest.

When lactose is not present, the repressor protein is bound to the operator because their shapes fit exactly. RNA polymerase binds to the promoter to perform transcription but is unable to because the repressor protein is blocking the way. When lactose is present, a lactose molecule binds to the repressor protein, changing the shape of the protein so that the protein is no longer able to bind to the operator. Without the repressor protein blocking the way, the RNA polymerase is able to read the DNA and form mRNA for protein synthesis. The genes of interest code for enzymes that break down lactose, allowing the bacteria to gain energy from the lactose. When all of the lactose molecules are broken down, the cell no longer has a need for those enzymes. There are no more lactose molecules left to bind to the repressor proteins, so the repressor proteins bind to the operator once again to block transcription of the genes of interest.

This amazing process is how bacteria are able to turn genes on and off based on need in the environment. This process only applies to prokaryotic cells, not eukaryotic cells. Eukaryotic cells are much more complex, and scientists have not been able to fully understand gene expression in these cells just yet.