What is the Difference Between ssDNA and dsDNA

The main difference between ssDNA and dsDNA is that ssDNA has a linear structure, whereas dsDNA contains a helical structure.

ssDNA and dsDNA are two structures of DNA that occur in nature. They appear in the genomes of DNA viruses.  

Key Areas Covered

1. What is ssDNA
– Definition, Structure, Importance
2. What is dsDNA
– Definition, Structure, Importance
3. Similarities Between ssDNA and dsDNA
– Outline of Common Features
4. Difference Between ssDNA and dsDNA
– Comparison of Key Differences

Key Terms 

dsDNA, ssDNA

What is ssDNA

ssDNA (single-stranded DNA) is DNA with one strand created in DNA replication. DNA replication forms two single-stranded DNA molecules that join to form a double-stranded DNA molecule. However, ssDNA is a linear structure that is stable. In addition, some viruses contain ssDNA genomes. ssDNA viruses belong to the realm of Monodnaviria. Transcription of the ssDNA viruses is similar to dsDNA viruses. The replication of the single-stranded DNA first forms a double-stranded molecule by the DNA polymerase. Then, it synthesizes mRNA from DNA.

Figure 1: Canines Parvovirus

Furthermore, the genome of the ssDNA viruses is circular, and the type of replication is rolling circle replication (RCR). Endonucleases bound to the DNA cleave the positive strand to keep the negative strand as the template for DNA replication. Therefore, DNA polymerase synthesizes the positive strand from the 3’ OH end. Parvoviruses are an example of ssDNA viruses. 

What is dsDNA

dsDNA (double-stranded DNA) is the type of DNA that mainly occurs in the genomes of many organisms, including viruses, prokaryotes, and eukaryotes. Therefore, most dsDNA occurs inside the nucleus of living organisms. Some dsDNA can occur inside mitochondria and chloroplasts. Carrying genetic information for development, function, and reproduction is the function of dsDNA. Structure-wise, dsDNA contains two polynucleotide strands made up of DNA nucleotides. These strands are complementary to each other, and they are held together by hydrogen bonds that occur between nitrogenous bases.

Figure 2: dsDNA

Moreover, these two polynucleotide strands coil with each other to form a double helix. Also, each strand runs in antiparallel directions in the double helix. The two ends of the DNA molecule are named as 3’ and the 5’ end. 

Similarities Between ssDNA and dsDNA

• ssDNA and dsDNA are two types of DNA occurring in organisms’ genomes.
• Both types of DNA occur in viral genomes.
• Both types of DNA store genetic information.
• They are made up of DNA nucleotides.

Difference Between ssDNA and dsDNA

Definition

ssDNA refers to the single DNA strand created during the replication process of DNA, while dsDNA refers to the two DNA strands bonded by the Watson–Crick noncovalent chemical bonds.

Structure

ssDNA is a linear structure that contains one DNA strand, while dsDNA has two DNA strands bound together by hydrogen bonding. 

Genomes

A few viruses contain ssDNA in their genomes, while most organisms contain dsDNA in their genomes.

Stability

ssDNA is a less stiff, stable structure, while dsDNA is comparatively more rigid and stable. 

Purine Pyrimidine Ratio

ssDNA contains a highly variable purine: pyrimidine ratio, while dsDNA contains a constant purine: pyrimidine ratio. 

Conclusion

In brief, ssDNA and dsDNA are two forms of DNA that occur in nature. ssDNA contains a single strand of DNA with a linear structure. A few viral genomes contain ssDNA in their genomes. Also, ssDNA contains a highly variable purine: pyrimidine ratio. In contrast, dsDNA has two DNA strands bound with hydrogen bonds. However, most organisms contain ds DNA in their genome. Importantly, dsDNA is stiffer and more stable than ssDNA. Its purine-to-pyrimidine ratio is constant. Therefore, the main difference between ssDNA and dsDNA is their structure. 

References:

1. Malathi VG, Renuka Devi P. ssDNA viruses: key players in global virome. Virusdisease. 2019 Mar;30(1):3-12. doi: 10.1007/s13337-019-00519-4. Epub 2019 Apr 19. PMID: 31143827; PMCID: PMC6517461.
2. Todorov TI, Morris MD. Comparison of RNA, single-stranded DNA and double-stranded DNA behavior during capillary electrophoresis in semidilute polymer solutions. Electrophoresis. 2002 Apr;23(7-8):1033-44. doi: 10.1002/1522-2683(200204)23:7/8<1033::AID-ELPS1033>3.0.CO;2-7. PMID: 11981850.

Image Courtesy:

1. “Canines Parvovirus” By Dre – Own work (CC-BY SA 3.0) via Commons Wikimedia
2. “Phosphate backbone” By National Human Genome Research Institute – Own Work (Public Domain) via Commons Wikimedia