Difference Between ssRNA and dsRNA

The key difference between ssRNA and dsRNA is that ssRNA has only one strand of RNA while dsRNA is made up of two complementary siRNA or miRNA strands.

RNA or ribonucleic acid is a type of nucleic acid which is made up of ribonucleotides. Generally, RNA is a single-stranded molecule, unlike DNA double helix. In the Baltimore classification of viruses, Group III, Group IV and Group V include RNA viruses. Some viruses have an ssRNA or single-stranded RNA genome. Therefore, their genome is made from one strand of RNA. Moreover, some viruses have dsRNA or double-stranded RNA genome. Therefore, their genome is made from two complementary strands of RNA. Sucrose or caesium chloride density gradient technique can separate ssRNA viruses and dsRNA viruses. Lighter particles are ssRNA viruses, while denser particles contain dsRNA.

CONTENTS

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

What is ssRNA?

ssRNA stands for single-stranded RNA. Generally, RNA is single-stranded. There are viruses having ssRNA genome. They are two types: positive sense and negative sense based on the sense or polarity of RNA. Positive sense single-stranded RNA behaves as mRNA. Hence, it can directly translate into a protein. Negative sense ssRNA is complementary to mRNA. Hence, it should be converted into positive-sense ssRNA by RNA dependant RNA polymerase. After that, it can translate into a protein.

Figure 01: RNA Viruses

In Baltimore classification, positive sense ssRNA viruses belong to Group IV while negative-sense ssRNA viruses belong to Group V. In sucrose or caesium chloride density gradients, lighter particles contain ssRNA viruses.

What is dsRNA?

dsRNA stands for double-stranded RNA. In dsRNA, there are two complementary strands of RNA. These strands are paired with each other by forming bonds between complementary bases. Unlike ssRNA, dsRNA is not long – it is a short molecule. dsRNA is formed when complementary DNA strands are transcribed into RNA by symmetrical transcription from opposing promoters. Moreover, ssRNA can form intra-strand double helixes which are dsRNA by complementary base pairing. dsRNA can also be formed by base pairing of complementary ssRNAs resulting from transposons and repetitive genes.

Figure 02: dsRNA Virus

Some viruses have dsRNA genomes. These viruses have a wide host range. Rotaviruses and picobirnaviruses are dsRNA viruses. The dsRNA genome of these viruses is transcribed into mRNA by RNA dependant RNA polymerase. Then, mRNA molecules translate into viral proteins. Furthermore, the positive sense RNA strand again can be used to produce dsRNA genomes for new viral particles. In the Baltimore classification, dsRNA belongs to Group III. dsRNA viruses infect all organisms including mammalians, bacteria, plants and fungi.

Small interfering RNA or siRNA is a type of dsRNA which can trigger RNA interference in eukaryotes, as well as interferon response in vertebrates.

What are the Similarities Between ssRNA and dsRNA?

• There are viruses having ssRNA and dsRNA.
• A single-stranded RNA molecule can undergo complementary base pairing to form intrastrand double helixes which are dsRNA.
• Both ssRNA and dsRNA are made from ribonucleotides having four bases; adenine(A), cytosine (C), guanine (G), or uracil (U), a ribose sugar and a phosphate group.

What is the Difference Between ssRNA and dsRNA?

The key difference between ssRNA and dsRNA is that ssRNNA has only one strand, while dsRNA has two complementary RNA strands paired together. In nature, ssRNA is found abundantly while dsRNA is less abundant. In the Baltimore classification, ssRNA viruses are in Group IV and V, while dsRNA viruses are in Group III.

The below infographic shows the difference between ssRNA and dsRNA in tabular form.

Summary – ssRNA vs dsRNA

In nature, RNA is found as a single-stranded molecule which is folded onto itself. mRNA is the single-stranded RNA molecule which translates into a protein on ribosomes. Many viruses have RNA genomes. Some viruses have ssRNA genomes while some viruses possess dsRNA genomes. dsRNA has two complementary RNA strands paired together. Positive sense ssRNA directly acts as mRNA and translates into viral proteins while negative sense ssRNA is converted into positive-sense ssRNA by RNA dependant RNA polymerase and then translated into proteins. dsRNA is transcribed into mRNA by RNA dependant RNA polymerase, and then the mRNA molecules translate into viral proteins. Thus, this summarizes the difference between ssRNA and dsRNA.

Reference:

1. “RNA.” Wikipedia, Wikimedia Foundation, 29 Nov. 2020, Available here.
2. Weber, Friedemann, et al. “Double-Stranded RNA Is Produced by Positive-Strand RNA Viruses and DNA Viruses but Not in Detectable Amounts by Negative-Strand RNA Viruses.” Journal of Virology, American Society for Microbiology, May 2006, Available here.

Image Courtesy:

1. “18 2014 1695 Fig1 HTML” By Aartjan J. W. te Velthuis (CC BY 4.0) via Commons Wikimedia
2. “Double-stranded RNA” By Supyyyy – Own work (CC BY-SA 4.0) via Commons Wikimedia

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