Difference Between hnRNA and mRNA

The key difference between hnRNA and mRNA is that hnRNA is the unprocessed premature mRNA transcript that contains introns while mRNA is the processed RNA that does not contain introns.

There are different types of RNA, and hnRNA and mRNA are two types of them. Heterogeneous nuclear RNA, also known as pre-mRNA, is a type of primary transcript produced inside the nucleus. Once pre-mRNA is made, it is post-transcriptionally processed into functional mRNA, which can be translated into a protein in the cytoplasm. Therefore, hnRNA is synthesized from a DNA template, and it is a newly formed RNA prior to processing. mRNA is the RNA sequence that carries the genetic information to produce a protein. It is a form of RNA after processing. Moreover, mRNA carries genetic codons from the DNA in the nucleus to the ribosomes for the protein synthesis.

CONTENTS

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

What is hnRNA?

Heterogeneous nuclear RNA or pre-mRNA is the RNA newly formed from the template DNA strand. It is a form of unmodified RNA. Therefore, it is a type of RNA before processing. hnRNA represents various types and sizes of RNA found within the nucleus. Majority of hnRNA serves as the precursor for mRNA. Once made, hnRNA undergoes splicing process and becomes mRNA in the cytoplasm. hnRNA may also be included in some nuclear RNA that do not become cytoplasmic mRNA.

RNA polymerase is the enzyme that catalyzes the copying of DNA into hnRNA inside the nucleus. Then hnRNA is processed within the nucleus and transported to the cytoplasm. Through the splicing process, all the introns are removed from hnRNA. Then a poly-A tail is added to the 3′ end, and a 5′ cap is added to the 5′ end of the RNA.

What is mRNA?

mRNA or messenger RNA is a single-stranded RNA sequence that contains the genetic information of a gene to produce a protein. It is a form of RNA after processing. Therefore, it only contains the exons of the gene. mRNA is derived from pre-mRNA, which is the primary transcript. Once made, mRNA leaves the nucleus and reaches a ribosome in the cytoplasm in order to translate and produce a protein. Ribosomes read nucleotide triplets (codons) of mRNA and add corresponding amino acids according to the codons. Likewise, ribosomes produce amino acids sequences from mRNAs during the translation.

The processing and transporting of mRNA differ among eukaryotes and prokaryotes. Eukaryotic mRNA requires extensive processing and transport while prokaryotic mRNA does not. Prokaryotic mRNA synthesis takes place in the cytoplasm itself, and once made, it is immediately ready to undergo translation without processing.

What are the Similarities Between hnRNA and mRNA?

• hnRNA and mRNA are two types of RNA found in cells.
• hnRNA contains mRNA precursors.
• In fact, the majority of hnRNA is processed into mRNA.
• Both hnRNA and mRNA are single-stranded RNA.
• They are needed for the synthesis of proteins in cells.

What is the Difference Between hnRNA and mRNA?

The key difference between hnRNA and mRNA is that the hnRNA is the newly formed RNA before processing, while mRNA is the RNA after processing. Also, hnRNA is derived directly from the DNA template by RNA polymerase while mRNA is derived from hnRNA.

Moreover, hnRNA undergoes splicing and capping. But, mRNA is not subject to splicing or capping; it translates into a protein. Besides, another difference between hnRNA and mRNA is that hnRNA contains introns, while mRNA does not contain introns.

Summary – hnRNA vs mRNA

hnRNA is the newly formed RNA from a DNA template. It is kind of unmodified RNA. Majority of hnRNA undergoes processing and becomes mRNA. mRNA is the single-stranded RNA after processing. It contains genetic codons to synthesize a specific protein. Therefore, mRNA base sequence is complementary to one sequence of the gene. mRNA does not contain introns. It contains exons. Thus, this summarizes the difference between hnRNA and mRNA.

Reference:

1. “Primary Transcript”. En.Wikipedia.Org, 2020, Available here.
2. “Translation: DNA To Mrna To Protein | Learn Science At Scitable”. Nature.Com, 2020, Available here.

Image Courtesy:

1. “Pre-mRNA” By Nastypatty – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “MRNA structure” By Daylite – Own work (Public Domain) via Commons Wikimedia