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If the level of lactose is low what happens to the lac operon system? What would happen is lactose would added in the system?

2006-11-06 11:33:35 · 2 answers · asked by Shane 1 in Science & Mathematics Biology

2 answers

Bacterial cells cannot use lactose without first breaking it down into simpler sugars. That is what the Lac Operon Genes are responsible for, however, transcription and translation are very energy demanding and in order to optimize resource use, bacteria have evolved the Lac Operon System consisting of a CAP (cAMP Activator Protein) binding site, a promoter, a repressor, an operator and operon genes.

Levels of Lactose determine whether the lac I repressor (a DNA binding protein) is attached to the operator (specific DNA sequence between the promoter and Lac Operon Genes). The Lac I repressor is always expressed and at any one time can be either bound to DNA or lactose depending on lactose concentration. When there are low levels of lactose, the repressor is bound to the operator and literally blocks transcription of Lac Operon Genes because of the position of the operator. When the repressor is bound, RNA polymerase cannot transcribe.

When lactose is added to the system, the repressor comes off the DNA because of its higher affinity to lactose. Thus transcription can occur. However, the promoter is not good at recruiting RNA polymerase and the proteins (Lac Operaon Genes) required to break down lactose are lowly expressed. As a result, the cell starves and creates a chemical called cAMP. This cAMP recruits the CAP to the CAP binding site and RNA polymerase activity is enhanced. Lac Operon Genes are expressed, lactose is broken down to glucose and galactose, lowering the lactose concentration and placing represson back on the operator. The cell uses the simpler sugars for energy and the cAMP signal stops and CAP goes away.

2006-11-06 12:10:12 · answer #1 · answered by Jeff P 2 · 0 0

lac operon sys is under -ve control.

2016-05-22 05:30:49 · answer #2 · answered by ? 4 · 0 0

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