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Lactose Operon Dean Williams
An Operon is a section of DNA that contains structural genes, Control elements and regulatory genes which are
used to control protein synthesis and switch particular genes on or off in different conditions within organisms.
Structural Genes The section of DNA that codes for useful proteins such as the enzymes -
galactosidase and Lactose Permease to break down lactose in E.Coli bacterium.
Control Elements Made up of two sections of DNA which include a Promoter and an
The Promoter section of DNA promotes the initiation of the Transcription step of
Protein Synthesis, the first of two, by allowing RNA Polymerase to bind to it.
The Operator section of DNA decides how quickly the operations of Protein
Synthesis occur because Transcription Factors are allowed to bind to this section of
the DNA allowing the rate of Transcription to be altered .
Regulatory Genes The section of DNA that comes before the Promoter region which codes
for Transcription factors that alter the rate of Transcription .
Transcription Factors that increase the rate of Transcription are called Activators.
Transcription Factors that decrease the rate of Transcription are called Repressors.
An example of the control of protein synthesis using Operons is the use of the Lac operon in E.Coli bacteria where
the production of the enzymes -galactosidase and lactose Permease is inhibited by the use of a repressor when
the Lactose is not present. These steps include:
1. The regulatory genes produce repressors called Lac Repressors that bind to the Operator region of the
Operon on the DNA sequence which means that no other Transcription factors can bind to it such as Lac
Activators that would initiate the process of transcription of the enzymes -galactosidase and Lactose
Permease. This occurs when there is no Lactose present since the enzymes that break down Lactose are
2. When Lactose is present, however, a Lactose molecule binds to the Lac Repressor that's bound to the
Operator region which notifies that Lactose sugar is present and needs to be broken down. This changes
the shape of the Lac Repressor which causes it to break bonds with the Operator region which allows
other Transcription factors such as activators to initiate and increase the rate of transcription. The
structural genes lacZ, lacY and lacA are allowed to be Transcribed .