Gene Regulation: Lac Operon & Trp Operon | NEET Biology
Gene Regulation: Operon Concept, Lac Operon and Trp Operon
Gene regulation refers to the mechanism by which the expression of some genes is promoted while the expression of other genes is inhibited. Gene regulation is influenced by metabolic (physiological) and environmental conditions.
Gene Regulation in Prokaryotes – Operon Concept
The operon concept was proposed by Jacob and Monod while studying gene regulation in Escherichia coli bacteria.
- It is applicable to gene regulation in prokaryotes.
- It mainly operates at the transcriptional level.
What is an Operon?
An operon is a group of genes that are expressed and regulated together as a functional unit.
Components of an Operon
- Structural genes
- Operator gene
- Promoter
- Regulatory gene
1. Structural Gene
A structural gene is responsible for the synthesis of polypeptides or enzymes that participate in metabolic pathways. Structural genes contain coded information required for the synthesis of functional products.
2. Operator Gene
The operator acts like an ON/OFF switch and regulates the activity of the structural genes.
3. Promoter
The promoter provides the site for attachment of RNA polymerase, the enzyme involved in transcription.
4. Regulatory Gene
The regulatory gene synthesizes or regulates the production of a special type of protein called a repressor. It is involved in controlling the activity of the operon.
Important Regulatory Components
- Repressor
- Inducer
- Aporepressor
- Corepressor
Types of Operons
There are two major types of operons:
- Inducible operon
- Repressible operon
Inducible Operon – Lac Operon
The lac operon is an inducible operon involved in the utilization of lactose in bacteria such as E. coli.
When lactose is available, it ultimately permits transcription of the structural genes involved in lactose metabolism.
Basic Organization of Lac Operon
- i = regulatory gene
- p = promoter
- o = operator
- z, y, a = structural genes
Structural Genes of Lac Operon
The three structural genes are:
- lac Z
- lac Y
- lac A
These genes encode proteins involved in lactose utilization.
Repressible Operon – Trp Operon
The trp operon is a repressible operon involved in the anabolic pathway of tryptophan synthesis.
The trp operon contains five structural genes, which code for enzymes involved in tryptophan biosynthesis.
When sufficient tryptophan is available, it acts as a corepressor and helps switch off the operon.
Gene Regulation in Eukaryotes
In eukaryotes, gene regulation occurs at several levels. This allows cells to precisely control when and where genes are expressed.
- Transcriptional level
- Translational level
- Post-transcriptional level
- During and after translation / protein processing
NEET Quick Revision
- Operon concept: Jacob and Monod
- Lac operon: Inducible operon
- Trp operon: Repressible operon
- Operator: Acts as an ON/OFF regulatory switch
- Promoter: Site for RNA polymerase attachment
- Lac structural genes: lac Z, lac Y and lac A
- Trp operon: Involved in tryptophan biosynthesis
Frequently Asked Questions
What is gene regulation?
Gene regulation is the mechanism by which gene expression is controlled, including the promotion or inhibition of gene activity.
Who proposed the operon concept?
The operon concept was proposed by François Jacob and Jacques Monod.
What is the lac operon?
The lac operon is an inducible operon involved in lactose utilization in bacteria.
What is the trp operon?
The trp operon is a repressible operon involved in the biosynthesis of tryptophan.
What is the function of the promoter?
The promoter provides the binding site for RNA polymerase and plays an important role in initiating transcription.
Also Read: Molecular Basis of Inheritance, Transcription, Translation, Lac Operon and Regulation of Gene Expression.
Keywords: gene regulation, operon concept, lac operon, trp operon, inducible operon, repressible operon, regulatory gene, structural gene, promoter, operator gene, NEET Biology, CBSE Class 12 Biology, molecular basis of inheritance.
