Schematic diagram of bacterial lactose operon
Some genes are switched on and off depending on the function of the cell. Genes that code for vital metabolites, i.e. essential proteins always remain switched on.
There is a model hypothesized by two famous scientists, Jacob and Monod that illustrates how certain genes can be active or inactive.
The following diagrams the basics of their model of an operon (where it is possible for there to be more than one structural gene and operator gene). The goal of these genes is to breakdown lactose (a sugar) when it is present in the cell.
When lactose is absent, the repressor molecule attaches itself to the operator gene, effectively switching it off.
Sometimes for hereditary reasons, or mutations, the biochemical pathway cannot be fully executed, due to a dysfunctional or missing gene.
Hereditary defects are known as inborn errors of metabolism, and are present since birth. Mutations can occur at the initial meiotic stages in the formation of gametes and are possible throughout an organism’s lifetime preventing the induction of various enzymes.
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