Difference Between DNA and RNA Viruses

Main Difference – DNA vs RNA viruses

A virus is a biological agent that can self-replicate inside a host cell. The infected cells by viruses may produce thousands of new copies of the original virus at an extraordinary rate. The genetic material of a virus can be either DNA or RNA. The viruses that contain DNA as their genetic material are called the DNA viruses. RNA viruses, on the other hand, contain RNA as their genetic material. The genetic material is covered by a protein capsid in all viruses. Some viruses contain an envelope covering the capsid. After infecting a host, the replication of the viral DNA occurs inside the nucleus while the replication of the viral RNA occurs in the cytoplasm. The main difference between DNA and RNA viruses is that DNA viruses contain large genomes due to the accurate replication whereas RNA viruses contain small genomes due to the error-prone replication.

Key Areas Covered

1. What are DNA Viruses
      – Definition, Classes, Biosynthesis
2. What are RNA Viruses
      – Definition, Classes, Biosynthesis
3. What are the Similarities Between DNA and RNA Viruses
      – Outline of Common Features
4. What is the Difference Between DNA and RNA Viruses
      – Comparison of Key Differences

Key Terms: Baltimore Classification, DNA Viruses, Double-Stranded DNA, Envelope, RNA Viruses, Single-Stranded DNA

What are DNA Viruses

DNA viruses refer to viruses whose genetic information is stored in the form of DNA. Most DNA viruses are double-stranded viruses, consisting of icosahedral symmetry in their capsid. Few may contain single-stranded DNA in their genome. Some DNA viruses may also contain an envelope.

Seven classes of viruses can be identified based on the type of genetic material present in each virus and their method of replication. This classification is called the Baltimore classification, which is shown in figure 1.

Figure 1: Baltimore Classification

Classes of DNA Viruses

Class	Type of Nucleic Acid	Family	Biosynthesis
Class I	Double-stranded, linear DNA	Adenoviridae (non-enveloped) Herpesviridae (enveloped) Poxviridae (enveloped)	Cellular enzyme transcribes viral DNA in nucleus in Adenoviridae and Herpesviridae Viral enzyme transcribes viral DNA in cytoplasm
Class II	Single-stranded, linear DNA (sense strand)	Parvoviridae (non-enveloped)	Cellular enzyme transcribes viral DNA in nucleus
Class VII	Double-stranded, circular DNA	Papovaviridae (non-enveloped) Hepadnaviridae (enveloped)	Cellular enzyme transcribes viral DNA in nucleus in Papovaviridae Cellular enzyme transcribes viral DNA in nucleus; reverse transcriptase copies mRNA to make viral DNA in Hepadnaviridae

What are RNA Viruses

RNA viruses refer to the viruses whose genetic information is stored in the form of RNA. Most RNA viruses contain single-stranded RNA while a few contain double-stranded RNA. RNA viruses contain small genomes when compared to DNA viruses. This is due to the error-prone replication in RNA viruses. Some DNA and RNA viruses are shown in figure 2.

Figure 2: DNA and RNA Viruses

Classes of RNA Viruses

Class	Type of Nucleic Acid	Family	Biosynthesis
Class III	Double-stranded RNA	Reoviridae (double-capsid, non-enveloped)	Viral enzyme copies antisense RNA strand to make mRNA in the cytoplasm
Class IV	Single-stranded RNA (sense strand)	Picornaviridae (non-enveloped) Togaviridae (enveloped)	Viral RNA functions as a template for synthesis of RNA polymerase which copies antisense strand RNA to make mRNA in the cytoplasm
Class V	Single-stranded RNA (antisense strand)	Rhabdoviridae (enveloped)	Viral enzyme copies viral RNA to make mRNA in the cytoplasm
Class VI	Single-stranded RNA (sense strand) reverse transcriptase (RNA-dependent DNA polymerase)	Retroviridae (enveloped)	Viral enzyme copies viral RNA to make DNA in the cytoplasm; DNA moves to nucleus

Similarities Between DNA and RNA Viruses

Both DNA and RNA viruses can only reproduce inside a living host cell.
Most DNA and RNA viruses can be harmful since they infect living cells.
Both DNA and RNA viruses contain a capsid.
Both DNA and RNA viruses can be either enveloped or non-enveloped.

Definition

DNA Viruses: DNA viruses refer to viruses whose genetic information is stored in the form of DNA.

RNA Viruses: RNA viruses refer to viruses whose genetic information is stored in the form of RNA.

Genome

DNA Viruses: DNA viruses contain DNA as their genetic material.

RNA Viruses: RNA viruses contain RNA as their genetic material.

Double-stranded/Single-stranded

DNA Viruses: Double-stranded DNA viruses are more common than single-stranded DNA viruses.

RNA Viruses: Single-stranded RNA viruses are more common than double-stranded RNA viruses.

Replication

DNA Viruses: Viral DNA is replicated inside the nucleus of the host cell.

RNA Viruses: Viral RNA is first transcribed and then is replicated in the cytoplasm.

Protein Synthesis

DNA Viruses: Viral DNA is first transcribed into RNA, and then mRNA is translated into viral proteins.

RNA Viruses: RNA viruses can bypass transcription during protein synthesis since they already contain RNA in the genome.

Stability

DNA Viruses: DNA viruses are stable due to the lower mutation rate.

RNA Viruses: RNA viruses are unstable due to the higher mutation rate.

Fidelity of Replication

DNA Viruses: DNA viruses shows an accurate replication.

RNA Viruses: RNA viruses shows an error-prone replication.

Size of the Genome

DNA Viruses: DNA viruses contain a large genome.

RNA Viruses: RNA viruses contain a small genome.

Procapsid

DNA Viruses: Newly-synthesized viral DNA is packed into a pre-formed capsid called procapsid.

RNA Viruses: Newly-synthesized viral RNA should be protected from degradation since a procapsid is not formed in RNA viruses.

Types

DNA Viruses: Class I, II, and VII of the Baltimore classification of viruses are DNA viruses.

RNA Viruses: Class III, IV, V, and VI of the Baltimore classification of viruses are RNA viruses.

Examples

DNA Viruses: Adenoviruses, Herpesviruses, Poxviruses, Parvoviruses, and Hepadnaviruses are the examples of DNA viruses.

RNA Viruses: Reoviruses, Picornaviruses, Togaviruses, Orthomyxoviruses, Rhabdoviruses, and Retroviruses are the examples of RNA viruses.

Associated Diseases

DNA Viruses: Smallpox, herpes, and chickenpox are diseases of DNA viruses.

RNA Viruses: Aids, Ebola hemorrhagic fever, SARS, the common cold, influenza, hepatitis C, West Nile fever, polio, and measles are some of the diseases caused by RNA viruses.

Conclusion

DNA and RNA viruses are two types of viruses with different types of genetic material. DNA viruses contain DNA in the genome while RNA viruses contain RNA. The replication of DNA viruses occurs inside the host’s nucleus while it occurs in the host’s cytoplasm in RNA viruses. The main difference between DNA and RNA viruses is the type of genetic material and replication inside the nucleus.

Reference:

1. “DNA Viruses.” DNA Viruses – STEP1 Microbiology – Step 1 – Medbullets.Com, Available here.
2. “RNA virus.” Wikipedia, Wikimedia Foundation, 20 Nov. 2017, Available here.

Image Courtesy:

1. “Baltimore Classification” By GrahamColm at English Wikipedia – Transferred from en.wikipedia to Commons by Moez using CommonsHelper (Public Domain) via Commons Wikimedia
2. “Figure 21 01 03” By CNX OpenStax (CC BY 4.0) via Commons Wikimedia