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A functional complex comprising a cluster of genes including structural gene, a promoter gene, an operator gene and a regulator gene was discovered by :-
[Uttaranchal PMT 2006]
  • a)
    Beadle and Tatum (1958)
  • b)
    Watson and crick (1953)
  • c)
    Jacob and Monad (1961)
  • d)
    Britten and Davidson (1961)
Correct answer is option 'C'. Can you explain this answer?
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Discovery of a Functional Complex Comprising Genes

The correct answer to the question is option 'C' - Jacob and Monod (1961).

Explanation:

- In 1961, François Jacob and Jacques Monod conducted groundbreaking experiments that led to the discovery of a functional complex comprising a cluster of genes. Their work focused on the regulation of gene expression in bacteria, specifically the lac operon system in E. coli.

The Lac Operon System:

- The lac operon is a cluster of genes involved in the metabolism of lactose in E. coli. It consists of three structural genes: lacZ, lacY, and lacA, along with a promoter gene (lacP), an operator gene (lacO), and a regulator gene (lacI).

Structural Genes:

- The structural genes in the lac operon are responsible for encoding enzymes involved in the breakdown of lactose. The lacZ gene encodes β-galactosidase, which breaks down lactose into glucose and galactose. The lacY gene encodes lactose permease, a transporter protein that allows lactose to enter the bacterial cell. The lacA gene encodes transacetylase, an enzyme involved in lactose metabolism.

Promoter Gene:

- The promoter gene (lacP) is a DNA sequence located upstream of the structural genes. It serves as the binding site for RNA polymerase, an enzyme that initiates transcription by binding to the promoter and synthesizing mRNA from the DNA template.

Operator Gene:

- The operator gene (lacO) is a DNA sequence located between the promoter and the structural genes. It acts as a switch that controls the expression of the structural genes. When a molecule called a repressor binds to the operator, it prevents RNA polymerase from binding to the promoter, thereby inhibiting transcription.

Regulator Gene:

- The regulator gene (lacI) is located upstream of the promoter gene. It encodes the lac repressor protein, which can bind to the operator and block RNA polymerase from initiating transcription. The lac repressor is synthesized in an inactive form, but it can be activated or deactivated by binding to a small molecule called an inducer.

Jacob and Monod's Experiments:

- Jacob and Monod used a combination of genetic and biochemical techniques to study the lac operon system in E. coli. They discovered that the lac repressor protein binds to the operator in the absence of lactose, preventing the expression of the structural genes. However, when lactose is present, it acts as an inducer and binds to the lac repressor, causing a conformational change that prevents it from binding to the operator. This allows RNA polymerase to bind to the promoter and initiate transcription of the structural genes.

- Through their experiments, Jacob and Monod established the concept of gene regulation and proposed the model of an inducible operon, where the lac operon is only expressed when lactose is available as a substrate.

- Their work on the lac operon system laid the foundation for our understanding of gene regulation and the molecular mechanisms involved in controlling gene expression. It has had a profound impact on the field of molecular biology and remains a classic example of gene regulation in prokaryotes.
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