What is the Difference Between Prokaryotic and Eukaryotic Gene Structure

The main difference between prokaryotic and eukaryotic gene structure is that the prokaryotic gene structure consists of operons and clusters of several functionally-related genes, whereas the eukaryotic gene structure does not contain operons. Furthermore, the introns present in the eukaryotic gene structure interrupts the open reading frame while there are no introns in the prokaryotic gene structure.

Prokaryotic and eukaryotic gene structure are two types of gene structures with different organizations. Both undergo transcription and translation to produce functional proteins.

Key Areas Covered

1. What is Prokaryotic Gene Structure
     – Definition, Structure, Behavior
2. What is Eukaryotic Gene Structure
     – Definition, Structure, Behavior
3. What are the Similarities Between Prokaryotic and Eukaryotic Gene Structure
     – Outline of Common Features
4. What is the Difference Between Prokaryotic and Eukaryotic Gene Structure
     – Comparison of Key Differences

Key Terms

Eukaryotic Gene Structure, Exons, Introns, Open Reading Frame, Polycistronic Operon, Prokaryotic Gene Structure

What is the Prokaryotic Gene Structure

Prokaryotic gene structure is the organization of the prokaryotic genes in the genome. The most significant feature of the prokaryotic gene organization is the presence of polycistronic operon, which are the clusters of genes with related functions. Therefore, the genes responsible for a particular function can be regulated altogether under a single promoter in prokaryotes.

Figure 1: Prokaryotic Gene Structure

Also, all the genes in the operon are transcribed into the same mRNA with a single ribosome binding site. Hence, the ribosome can translate all genes simultaneously. This process is known as transcriptional coupling. Here, the ribosome translocates to the next open reading frame at the end of the previous open reading frame. The presence of multiple open reading frames in the same mRNA molecule is only possible in prokaryotes since their transcription and translation occur at the same cellular location, which is in the cytoplasm.

What is Eukaryotic Gene Structure

Eukaryotic gene structure is the organization of the eukaryotic genes in the genome. Here, in the eukaryotic gene structure, the most significant feature is the presence of introns between the open reading frame, breaking it into pieces called exons. Only exons will remain in the mature mRNA as the removal of introns occurs during the post-transcriptional modifications in a process called RNA splicing. Generally, introns sequences are longer than exon sequences. Once spliced out, the eukaryotic mRNA contains a single, continuous protein-coding region. Apart from that, a 5’ cap and a 3’ poly A tail are added to the eukaryotic mRNA to increase the stability.

Figure 2: Eukaryotic Gene Structure

However, unlike prokaryotes, eukaryotic genes do not form clusters regulated by the shared regulatory elements. In addition, each eukaryotic gene has its own promoter and other regulatory elements. Therefore, the eukaryotic mRNA always contains a single open reading frame.

Similarities Between Prokaryotic and Eukaryotic Gene Structure

• Prokaryotic and eukaryotic gene structures are the structural organization of genes in the corresponding genomes.
• Both are made up of DNA and in the double-stranded molecule, one of the two strands (sense strand) encodes the information of a gene.
• Also, both types of gene structure contain common elements due to the shared ancestry of cellular life.
• Furthermore, in both, the open reading frame of the gene structure runs in the 5’ to 3’ direction.
• Moreover, the regulatory sequences of genes occur at the extremities of genes. This can be either next to the open reading fame like the promoter or separated by many kilo bases like enhancers and silencers. The promoter occurs at the 5’ end of the open reading frame.
• Additionally, start and stop codon flank the open reading frame. The 5’ UTR and the 3’ UTR regions flank the open reading frame from the outside of the start and the stop codons respectively.
• Besides, the 3’ UTR contains the transcription termination site, which marks the end point of transcription.

Difference Between Prokaryotic and Eukaryotic Gene Structure

Definition

Prokaryotic gene structure refers to the gene structure of prokaryotes, which mainly comprises the operon-based gene clusters while eukaryotic gene structure refers to the gene structure of eukaryotes whose open reading frame is disturbed by the presence of introns. Hence, this explains the fundamental difference between prokaryotic and eukaryotic gene structure.

Open Reading Frame

Another difference between prokaryotic and eukaryotic gene structure is that introns do not interrupt the open reading frame of the prokaryotic gene structure while introns interrupt the open reading frame of the eukaryotic gene structure.

Operons

The functionally-related genes of the prokaryotic gene structure occur in operons while individual promoters regulate the genes of the eukaryotic gene structure. Thus, this is another difference between prokaryotic and eukaryotic gene structure.

Conclusion

Prokaryotic gene structure is the organization of the prokaryotic genes in the genome, mainly characterized by the presence of operons, the clusters of functionally-related genes. On the other hand, the main characteristic feature of the eukaryotic gene structure is the presence of introns, which cluster the open reading frame into exons. Therefore, the main difference between prokaryotic and eukaryotic gene structure is the structural organization of the functional units of a gene.

Reference:

1. Shafee T, Lowe R (2017). “Eukaryotic and prokaryotic gene structure”. WikiJournal of Medicine. 4 (1). doi:10.15347/wjm/2017.002. 

Image Courtesy:

1. “Gene structure prokaryote 2 annotated” By Thomas Shafee – Shafee T, Lowe R (2017). “Eukaryotic and prokaryotic gene structure”. WikiJournal of Medicine 4 (1). DOI:10.15347/wjm/2017.002. ISSN 20024436. (CC BY 4.0) via Commons Wikimedia  
2. “Gene structure eukaryote 2 annotated” By Thomas Shafee – Shafee T, Lowe R (2017). “Eukaryotic and prokaryotic gene structure”. WikiJournal of Medicine 4 (1). DOI:10.15347/wjm/2017.002. ISSN 20024436. (CC BY 4.0) via Commons Wikimedia