$lac$ Operon: Regulatory Protein Binding Status
This question concerns the state of the $lac$ operon's regulatory proteins under specific environmental conditions: very low concentrations of both lactose and glucose.
Repressor Protein Binding
The repressor protein controls the $lac$ operon by binding to the operator region. Lactose normally acts as an inducer, binding to the repressor and causing it to detach from the operator.
- Condition: Low lactose concentration.
- Effect: Lactose cannot effectively bind to the repressor.
- Result: The repressor protein remains bound to the operator region, blocking transcription.
cAMP-CAP Complex Binding
The Catabolic Activator Protein (CAP), when bound to cyclic AMP (cAMP), forms the cAMP-CAP complex. This complex enhances the initiation of transcription at the $lac$ operon promoter. Glucose levels influence cAMP concentration inversely.
- Condition: Low glucose concentration.
- Effect: Low glucose leads to high intracellular cAMP levels. cAMP binds to CAP, forming the cAMP-CAP complex.
- Result: The cAMP-CAP complex binds to the CAP binding site near the promoter.
Combined Binding Status
Considering both conditions:
- The repressor is bound to the operator due to low lactose.
- The cAMP-CAP complex is bound to the CAP binding site due to low glucose.
Therefore, when both lactose and glucose are at very low concentrations, both the repressor and the cAMP-CAP complex are bound to their respective sites on the DNA.
Conclusion
The binding status is that both the repressor and cAMP-CAP complex remain bound to their respective binding sites (operator and CAP binding site, respectively).
Important Questions from Regulation of Gene Expression
- Which of the following conditions induce(s) the expression of $ \beta$-galactosidase gene in the lac operon?
Determine the correctness or otherwise of the following Assertion [a] and the Reason [r].
Assertion [a]: In multicellular organisms, cells of different lineages have different gene expression profiles.
Reason [r]: Alternative splicing is the only mechanism to generate protein diversity.- The event(s) that lead(s) to inactivation of tumor suppressor genes in cancer cells is(are)
- Which of the following statement(s) is(are) CORRECT regarding the $lac$ operon in $E. coli$ when grown in the presence of glucose and lactose?
Determine the correctness or otherwise of the following Assertion [a] and the Reason [r]
Assertion: Ab initio gene finding algorithms that predict protein coding genes in eukaryotic genomes are not completely accurate.
Reason: Eukaryotic splice sites are difficult to predict.
