What is the Difference Between Prokaryotic and Eukaryotic mRNA

The main difference between prokaryotic and eukaryotic mRNA is that prokaryotic mRNA is polycistronic, whereas eukaryotic mRNA is monocistronic. Furthermore, several structural genes of an operon are transcribed into a single mRNA while eukaryotic mRNA contains a single gene transcribed into an mRNA molecule. In addition to these, transcription is coupled with translation in prokaryotes while transcription of eukaryotes occurs after the completion of transcription. 

Prokaryotic and eukaryotic mRNA are the two products of transcription of prokaryotes and eukaryotes. 

Key Areas Covered 

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

Key Terms 

Eukaryotic mRNA, Monocistronic, Polycistronic, Prokaryotic mRNA, Transcription, Translation

What is Prokaryotic mRNA 

Prokaryotic mRNA is the type of mRNA that occurs in prokaryotes as a result of transcription. Generally, RNA polymerase is responsible for the transcription of genes into mRNA molecules. However, the main feature of prokaryotic mRNA is polycistronic. Therefore, a single mRNA molecule contains several structural genes, which belong to a particular operon. Thus, the same mRNA molecule consists of several sites for the initiation and termination of polypeptides. It is why a single prokaryotic mRNA molecule can synthesize several types of proteins.

Figure 1: Prokaryotic mRNA

Furthermore, transcription of prokaryotes is always coupled with translation. Therefore, the translation of prokaryotic mRNA starts while the DNA template is being transcribed. Therefore, prokaryotic mRNA molecules undergo very little post-transcriptional modifications. They tend to degrade quickly by ribonucleases, reducing the lifespan of prokaryotic mRNA.  

What is Eukaryotic mRNA 

Eukaryotic mRNA is the result of transcription of eukaryotic genes by RNA polymerases. Eukaryotic genes occur individually. Therefore, a single eukaryotic mRNA contains a single coding region of a gene. However, one most significant difference between prokaryotic and eukaryotic mRNA is that eukaryotic mRNA undergoes significant changes during post-transcriptional modifications. Basically, these modifications include polyadenylation or the addition of a poly-A tail at the 3′ OH group, the addition of a 5′ cap, methylation, etc. More importantly, post-transcriptional modifications increase the stability of the eukaryotic mRNA.

Figure 2: Eukaryotic mRNA

Moreover, eukaryotic genes contain introns, interrupting the coding region. Therefore, the process of removing introns from the coding regions is splicing. Alternative splicing can produce different coding regions by alternatively splicing the exons. Furthermore, transcription of eukaryotes occurs inside the nucleus. However, mature mRNAs, after undergoing post-transcriptional modifications, move into the cytoplasm to undergo translation. Thus, transcription and translation in eukaryotes are completely separate events.  

Similarities Between Prokaryotic and Eukaryotic mRNA  

• Prokaryotic and eukaryotic mRNA are two types of mRNA molecules produced during transcription.  
• Their building blocks are RNA nucleotides.  
• Moreover, they are single-stranded structures with no base pairing.  
• They encode information on genes necessary for the synthesis of proteins.  
• Three bases on mRNA form a codon, representing a single amino acid on the protein.  
• Both contain two codons: start and stop codon. The start codon of both prokaryotic and eukaryotic mRNA is AUG.  
• Translation of both types of mRNA occurs in the cytoplasm. 

Difference Between Prokaryotic and Eukaryotic mRNA 

Definition 

Prokaryotic mRNA refers to the mRNA produced by the transcription of operons in prokaryotes, while eukaryotic mRNA refers to the mRNA produced by the transcription of single genes in eukaryotes. 

Synthesis 

The synthesis of prokaryotic mRNA occurs in the cytoplasm, while the synthesis of eukaryotic mRNA occurs inside the nucleus. 

Type 

Moreover, prokaryotic mRNA is polycistronic while eukaryotic mRNA is monocistronic. 

5′ Cap and 3′ Tail 

Prokaryotic mRNA does not contain both 5′ cap and 3′ tail while eukaryotic mRNA contains both 5′ cap and 3′ tail. 

Translation 

While the transcription is coupled with translation in prokaryotes, the transcription of eukaryotes occurs after the completion of transcription. 

Ribosome Binding Site 

Prokaryotic mRNA contains a ribosome-binding site, which is a Shine Dalgarno sequence, while 5′ cap in the eukaryotic mRNA is responsible for recruiting ribosomes. 

Life Span 

The lifespan of prokaryotic mRNA is very short, while eukaryotic mRNA is relatively stable.  

Post Transcriptional Modifications 

Prokaryotic mRNA undergoes very little post-transcriptional modifications while eukaryotic mRNA undergoes major post-transcriptional modifications. 

Conclusion 

Basically, prokaryotic mRNA is the type of mRNA produced by prokaryotes. Moreover, it is polycistronic, consisting of several structural genes of a particular operon. Prokaryotic mRNA undergoes very little post-transcriptional modifications. In contrast, eukaryotic mRNA is the type of mRNA in eukaryotes, consisting of the coding region of a single gene. However, it undergoes major post-transcriptional modifications including the addition of a 5′ cap and 3′ tail, splicing, etc. Therefore, the main difference between prokaryotic and eukaryotic mRNA is their structure and modifications. 

References:

1. Ashwathi, P. “Prokaryotic MRNAs and Eukaryotic MRNAs: Biochemistry.” Biology Discussion, 28 Nov. 2016, Available Here.

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. (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. (CC BY 4.0) via Commons Wikimedia