Difference Between Structural and Regulatory Genes

The main difference between structural and regulatory genes is that structural genes encode for proteins or RNA with structural and functional properties, whereas regulatory genes encode for transcription factors or regulatory RNA responsible for the regulation of expression of structural genes. 

Structural and regulatory genes are two types of genes found in genomes. They are responsible for the production of gene products based on the requirement of the cell. Moreover, the expression of a particular structural gene is regulated by a specific regulatory gene, while these regulatory genes mainly occur 5′ to the transcription start site of the structural gene. 

Key Areas Covered 

1. What are Structural Genes
     – Definition, Features, Importance
2. What are Regulatory Genes
     – Definition, Features, Importance
3. What are the Similarities Between Structural and Regulatory Genes
     – Outline of Common Features
4. What is the Difference Between Structural and Regulatory Genes
     – Comparison of Key Differences

Key Terms 

Gene Expression, Protein, Regulatory Genes, Structural Genes, Transcription Factors

What are Structural Genes 

Structural genes are the genes that encode either for RNA or proteins with a function other than the regulation of gene expression. Generally, structural genes occur in both prokaryotes and eukaryotes. Moreover, the gene products of structural genes can be either enzymes, hormones or proteins, which form structural components of the cell. Additionally, some structural genes encode for non-coding RNAs, including rRNAs and tRNAs. 

Figure 1: Expression of a Structural gene

Furthermore, in eukaryotes, structural genes are composed of exons and introns. Here, exons belong to the coding sequence that is interrupted by the non-coding intron sequences. Therefore, structural genes in eukaryotes are large in size. Moreover, after transcription, pre-mRNA molecule undergoes alternative splicing to join exons in different patterns prior to undergoing translation. On the other hand, functionally-related structural genes in prokaryotes occur in clusters called operons. Here, regulator factors affect all genes in the operon. For example, lacZ, lacY, and lacA are three structural genes in the lac operon. 

What are Regulatory Genes 

Regulatory genes are the genes that encode for regulator factors. These regulatory factors control the expression of one or several genes. Generally, regulatory genes occur upstream to the structural gene regulated by the regulatory gene. However, regulatory genes sometimes can occur downstream to their structural genes. Also, some regulatory genes occur far away from the structural gene in the genome. 

Figure 2: Regulatory and Structural Genes of Trp Operon

Moreover, the gene products of the regulatory genes can be either protein, which serves as transcription factors, or regulatory RNAs. Here, transcription factors bind to the promoter or operator region of the structural gene. In other words, transcription factors operate at the DNA level. Also, their binding either induce or repress the expression of the structural gene. In the lac operon, CAP (catabolite activator protein) is the activator, while the gene product of the lac I gene is the repressor. On the other hand, regulatory mRNAs, including siRNA and miRNA, act on the RNA transcribed from the structural gene. Their mechanism of action is commonly known as RNA interference. 

Similarities Between Structural and Regulatory Genes 

• Structural and regulatory genes are the two types of genes in the genome of both prokaryotes and eukaryotes. 
• They undergo transcription and translation. 
• Moreover, they undergo folding to produce 3D structures. 

Difference Between Structural and Regulatory Genes 

Definition 

Structural genes refer to a gene that codes for any RNA or protein product other than a regulatory factor, while regulatory genes refer to a gene involved in controlling the expression of one or more other genes. Thus, this is the main difference between structural and regulatory genes.

Encode for 

Another difference between structural and regulatory genes is that structural genes encode for proteins or RNA, while regulatory genes encode for transcription factors or regulatory RNA. 

RNAs 

Moreover, structural genes encode for mRNAs, rRNAs, and tRNAs, while regulatory genes encode for regulatory RNA such as miRNAs and siRNAs. 

The function of the Gene Product  

Besides, gene products of structural genes have either structural or functional importance, while regulatory genes regulate the expression of structural genes. 

Examples 

Lac Z, lac Y, and lac A genes of the lac operon, actin gene, etc. are the examples of structural genes, while lac I gene, CAP gene, etc. are the examples of regulatory genes. 

Conclusion 

Structural genes are the genes that encode for proteins or RNA that perform various functions in the cell other than the regulatory functions. Generally, the gene products of structural genes act as structural components of the cell or enzymes, hormones, transport proteins or other globular proteins. On the other hand, regulatory genes encode for transcription factors that regulate the expression of structural genes. Moreover, these transcription factors can be either activators, which activates gene expression, or repressors, which repress the expression of genes. Therefore, the main difference between structural and regulatory genes is their function. 

Reference:

1. Robb, Amanda. “Functional Differences of Structural & Regulatory Genes.” Study.com, Study.com, Available Here.

Image Courtesy:

1. “Bacterial Protein synthesis” By Joan L. Slonczewski, John W. Foster – Microbiology: An Evolving Science (CC BY-SA 3.0) via Commons Wikimedia   
2. “Trpoperon” By Histidine – Own work (CC BY-SA 3.0) via Commons Wikimedia