Difference Between Constitutive and Inducible Expression

The key difference between constitutive and inducible expression is that constitutive expression is the expression of a constitutive gene at a constant level while inducible expression is the expression of an inducible gene under certain conditions only.

Gene is the basic functional unit of heredity. Genes contain genetic codes to synthesize proteins. They are specific regions of chromosomes. To produce its product, a gene should undergo gene expression. Gene expression takes place via two steps: transcription and translation. Some genes known as constitutive genes are expressed continuously in the cell and synthesize their products. In contrast, some other genes known as inducible genes are expressed only under certain conditions when there is a necessity. A constitutive expression is the gene expression of constitutive genes, while inducible expression is the gene expression of inducible genes.

CONTENTS

1. Overview and Key Difference
2. What is Constitutive Expression
3. What is Inducible Expression
4. Similarities Between Constitutive and Inducible Expression
5. Side by Side Comparison – Constitutive vs Inducible Expression in Tabular Form
6. Summary

What is Constitutive Expression?

Constitutive gene is a gene that is expressed continuously in the cell and produces its products all the time at a constant rate. Thus, constitutive expression refers to the expression of a constitutive gene in an ongoing manner without regulation. These genes are mainly housekeeping genes involved in the processes vital for the cell function and survival of the organisms.

Glycolysis, citric acid cycle, transcription and translation are some of the processes occurring continuously in cells. The enzymes involved in these processes are continuously synthesizing and the constitutive gens code for those enzymes. They always remain ‘on’ state.

What is Inducible Expression?

Inducible gene is a gene expressed under certain conditions when there is a need for its products. For example, when a particular substrate is present, and it is necessary to metabolize it, inducible genes express and produce the required products to metabolize it. Thus, we call the expression of the inducible gene as inducible expression. Further, this is a regulated process.

The presence of a specific regulatory substance such as inducer or activator is essential in inducible gene expression. Specialty of this expression is that it takes place only when needed. Moreover, inducible gene expression occurs when there is an insufficient amount of a particular molecule within the cell. Lac operon present in bacteria is an example for inducible genes. Also, gene glucokinase is an example of an inducible gene in humans.

What are the Similarities Between Constitutive and Inducible Expression?

• Constitutive gene expression and inducible gene expression are two of the three types of gene expression.
• In both types, genes undergo transcription and translation.

What is the Difference Between Constitutive and Inducible Expression?

The constitutive expression refers to the expression of constitutive genes at a constant rate in a cell regardless of the environmental conditions. In contrast, the inducible expression refers to the expression of inducible genes under certain conditions. So, this is the key difference between constitutive and inducible expression. Furthermore, the constitutive genes remain on all the time while inducible genes turn on when only needed. Therefore, this is also a difference between constitutive and inducible expression.

The below infographic summarizes the difference between constitutive and inducible expression.

Summary – Constitutive vs Inducible Expression

There are three types of gene expression as constitutive, inducible and repressible. Constitutive gene expression is the constant expression of constitutive genes of a cell. In contrast, the inducible expression is the expression of inducible genes of a cell when required. So, this is the key difference between constitutive and inducible expression. Cells need the products of constitutive expression continuously while cells need the products of inducible expression on certain occasions.

Reference:

1. “Gene Expression.” Wikipedia, Wikimedia Foundation, 16 Aug. 2019, Available here.
2. “Gene Expression and Regulation” Nature News, Nature Publishing Group, Available here.

Image Courtesy:

1. “Gene expression” By Genomics Education Programme (CC BY 2.0) via Flickr
2. “Lac operon-2010-21-01” By Lac_operon.png: G3proderivative work: Tereseik (talk) – Lac_operon.png (CC BY 2.0) via Commons Wikimedia