Different Proteins Expressed from One Gene

Introduction

Gene Expression

Gene expression is the process by which information encoded in DNA is used to produce functional products, typically proteins. Each gene in our DNA carries the instructions for making a specific protein.

One Gene, Multiple Proteins

It is fascinating that a single gene can give rise to different proteins. This variability in protein production is a result of a mechanism called alternative RNA splicing, which allows for the production of different mature mRNA transcripts from the same primary transcript.

Alternative RNA Splicing

Definition

Alternative RNA splicing is a process that occurs during the maturation of mRNA. It involves the selective inclusion or exclusion of certain exons (coding regions) from the primary transcript to produce different mature mRNA transcripts.

Primary Transcript

The initial product of transcription is the primary transcript, which contains both coding regions (exons) and noncoding regions (introns).

Exons and Introns

Exons are coding regions that contain genetic information for protein synthesis, while introns are non-coding regions that do not code for proteins.

Mechanism of Alternative RNA Splicing

Selection of Exons

During alternative RNA splicing, different combinations of exons may be selected for inclusion or exclusion in the mature mRNA transcript.

Variability

This process introduces variability in the final mRNA product. Depending on which exons are retained or skipped, different mature mRNA transcripts can be produced.

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Different Proteins Expressed from One Gene

Example of Different Protein Isoforms

Let's consider an example of how alternative RNA splicing can result in different protein isoforms from one gene:

1. Gene A

Gene A codes for a protein involved in cell adhesion, and it has three exons (A, B, and C).

2. Alternative Splicing

Depending on the splicing choices made during RNA processing, three different mature mRNA transcripts can be produced:

• Transcript 1: Exons A and B are included, while exon C is excluded. This transcript leads to the production of Protein Isoform 1.
• Transcript 2: Exons A and C are included, while exon B is excluded. This transcript leads to the production of Protein Isoform 2.
• Transcript 3: All three exons (A, B, and C) are included. This transcript leads to the production of Protein Isoform 3.

3. Protein Isoforms

Protein Isoform 1, 2, and 3 have different functions or properties, and their presence or absence can have various effects on cell behaviour and function.

Functional Significance

Diverse Proteins

Alternative RNA splicing allows cells to produce a variety of proteins with different functions from a single gene. This diversification of proteins enhances an organism's adaptability and complexity.

Tissue-Specific Expression

Different tissues or cell types may preferentially splice the same gene in different ways, leading to the production of specific protein isoforms tailored to the needs of that tissue.

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Different Proteins Expressed from One Gene

Biological Examples

1. Dystrophin Gene

The dystrophin gene, associated with Duchenne muscular dystrophy, produces multiple protein isoforms through alternative splicing, each with distinct roles in muscle function.

2. Calcium Channels

Genes encoding calcium channels undergo alternative splicing, resulting in different isoforms of these channels, which play critical roles in nerve signalling and muscle contraction.

3. Neuronal Cells

In neuronal cells, alternative splicing of genes is common and contributes to the diversity of proteins involved in synaptic transmission, neuronal development, and plasticity.

Summary

In summary, different proteins can be expressed from a single gene due to alternative RNA splicing. This process allows for the selective inclusion or exclusion of exons during mRNA maturation, resulting in different mature mRNA transcripts. These transcripts can be translated into distinct protein isoforms with varying functions and properties. Alternative splicing contributes to the complexity and adaptability of organisms by enabling the production of diverse proteins tailored to specific cellular and tissue needs.