![]() This combination of conditions makes sense for the cell, because it would be energetically wasteful to synthesize the enzymes to process lactose if glucose was plentiful or lactose was not available. When lactose is present, it binds to the lac repressor and changes its shape so that it cannot bind to the lac operator to prevent transcription. In the absence of glucose, the binding of the CAP protein makes transcription of the lac operon more effective. Only when glucose is absent and lactose is present will the lac operon be transcribed ( Figure). First, the level of glucose must be very low or non-existent. However, for the lac operon to be activated, two conditions must be met. The Z gene of the lac operon encodes beta-galactosidase, which breaks lactose down to glucose and galactose. The lac operon encodes the genes necessary to acquire and process the lactose from the local environment. coli is able to use other sugars as energy sources when glucose concentrations are low. The lac operon is a typical inducible operon. ![]() ![]() The third type of gene regulation in prokaryotic cells occurs through inducible operons, which have proteins that bind to activate or repress transcription depending on the local environment and the needs of the cell. ![]()
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