Concept explainers
In the following diagram of the lac operon, an inducible operon, identify components a through i.
To identify: The components of an inducible operon, the lac operon.
Introduction: An operon is the functioning part of deoxyribonucleic acid (DNA). Each operon consists of a cluster of functionally related genes that share a single promoter and controlled by a shared operator. Lac operon is an inducible operon that controls the lactose metabolism in Escherichia coli and many other enteric bacteria.
Answer to Problem 1IQ
Pictorial representation: The components of lac operon are labeled in Fig.1.
Fig.1: Lac operon
Explanation of Solution
Lac operon is a group of genes with a single promoter. The genes in the lac operon encode proteins that allow a transport and metabolism of lactose in Escherichia coli.
- Regulatory gene (lacI): Regulatory gene controls the expression of other genes. The lac regulatory gene (lacI) codes for a repressor protein that can bind to the operator of the lac operon.
- Promoter: Promoter is the region adjacent to the operator in the lac operon, where the RNA polymerase binds to initiate a transcription of lactose genes. Promoter region switches on or off the gene expression through protein binding.
- Operator: Operator is the region that lies partially within the promoter in the lac operon. Operator region interacts with the regulatory protein that controls the transcription of the operon.
- Genes coding for enzymes: The lac operon consists of three genes such as lacZ, lacY, and lacA. lacZ gene transcribes as a single mRNA sequence. The lacZ gene encodes an enzyme β-galactosidase, lacY gene encodes an enzyme permease, and the lacA gene encodes trans-acetylase enzyme.
- Operon: Operon is the functional part of a DNA that consists of a group of functionally related genes regulated by a shared operator.
- RNA polymerase: RNA polymerase is an enzyme that synthesizes RNA and catalyzes the initiation and elongation of RNA using a process called transcription. In lac operon, RNA polymerase binds to the promoter region to initiate transcription.
- Active repressor: The activity of repressor (allosteric protein) may be determined by the presence or absence of the co-repressor. The repressor protein is produced by the regulatory gene and is activated by the association of a co-repressor. The activated repressor binds to the operator region, and it inhibits the transcription of lac operon genes.
- Inducer (allolactose): Inducer is allolactose, an isomer of lactose, which triggers or induces transcription. The inducer binds to and inactivates the repressor protein to induce the transcription of operon.
- mRNA for enzymes for lactose utilization: The genes of lac operon transcribe a single mRNA that encodes enzymes. The lacZ gene encodes an enzyme β-galactosidase, lacY gene encodes an enzyme permease, and the lacA gene encodes trans-acetylase enzyme for lactose utilization in Escherichia coli.
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