If every cell has the same DNA sequence, how do cells differ?
In Bacteria how is gene expression controlled?
ex. Lac operon - set of inducible genes involved in digestion of lactose. (can you explain the lac operon?)
Other Operons in bacteria
AraC Operon: Involved in the digestion of Arabinose.
When no arabinose present, the AraC repressor is bound to the operator and this prevents the RNA polymerase from binding therefore, no transcription of the "Arabinose Utilization Genes." When Arabinose is present, Arabinose binds to the AraC repressor which changes shape (but unlike the Lac Operon respressor), it stays bound, but moves out of the way which allows RNA Poly to come in and bind and transcribe the genes.
Trp Operon: Involved in the synthesis of Tryptophan (an amino acid)
When tryptophan is present, it is bound to the repressor (making the repressor "Active"). This keeps the repressor bound to the operon, thereby preventing transcription of the tryptophan synthesis genes. When there is no tryptophan in the environment, tryptophan is not bound to the repressor. The repressor changes shape and unbinds from the operon, allowing RNA polymerase to come in to transcribe the synthesis genes which will make tryptophan.
Can you answer the questions below about operons?
1. How are the 3 operons different?
2. How are they similar?
3. Why would bacteria not want to make proteins in certain conditions (ex. if there is no arabinose present in the environment?)
4. What does this have to do with our question of the term? (. how does the environment of the bacteria increase/decrease the transcription of certain genes which determines the 'trait' ex. being able to digest arabinose).
Operon video
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