In biology, viruses are small infectious agents, which invade living cells and take over the processes inside them. One way by which viruses can be classified is based on the nuclear structure of their cells. There are two major categories of viruses – DNA and RNA. In the following article, we will examine the differences between them.
DNA stands for deoxyribonucleic acid, which is a molecule that contains most of the genetic instructions of the body.
DNA viruses can be generally divided into three categories: adenoviruses, poxviruses, and inoviruses.
- Once the double-stranded DNA is injected into the host cell, it will enter the nucleus of the cell, where the viral DNA can possibly be integrated with the host cell’s DNA genome. Then, the viral DNA uses the cell’s polymerase enzymes to replicate the viral DNA and start producing replicas of the virus. One example of such DNA viruses, are adenoviruses.
- Some double-stranded DNA viruses carry their own polymerases; this which allows them to replicate within the cytoplasm of the infected cells, without going into the nucleus and using the cell’s own enzymes. One example of such DNA viruses are poxviruses. These DNA viruses are much less common the first category.
- One example of a single-stranded DNA viruse is the inovirus that infects bacterial cells.
RNA stands for ribonucleic acid, which is a molecule that plays a major role in the pathway from DNA to proteins.
When RNA viruses invade the human organism, they inject their RNA into the cytoplasm of the host cell. Once they are inside the cytoplasm, RNA can be used to synthesize proteins, and, eventually, to form replica viruses.
There is a special category of RNA viruses, which is called retroviruses. These viral agents contain protein known in biology as reverse transcriptase. Once the retrovirus injects its RNA into the cell, reverse transcriptase transcribes the RNA into DNA (the operation that is the reverse of normal transcription). This transcribed viral DNA, once synthesized, can then be incorporated into the host cell’s DNA. When the cell replicates, and eventually divides, it passes down the viral DNA portion to the replicated cells. One well-known example of the retrovirus that can infect the human organism is HIV (Human immunodeficiency) virus.
RNA viruses that contain RNA molecules serve directly as mRNA, and can be translated into proteins. These are called plus-strand RNA viruses (also known as positive strand RNA viruses). But, in minus-strand RNA viruses (also known as negative strand RNA viruses), the viral RNA must first be transcribed into the mRNA before it can be translated into proteins.
Single-stranded DNA viruses are much less common than double-stranded DNA viruses. With RNA viruses, it’s the opposite – there are some examples of double-stranded RNA viruses, but predominantly they are single-stranded.
The crucial difference between the two types of viruses is in their ability to synthesize proteins. While DNA viruses have to transcribe DNA into RNA in order to be able to synthesize proteins, RNA viruses can use their own viral RNA to do that.
|DNA Viruses||RNA Viruses|
|Double-stranded viruses are more common than single-stranded ones||Single-stranded viruses are more common than double-stranded ones|
|Replicate in the nucleus of the cell||Transcribe and replicate in the cytoplasm of the cell|
|Must first transcribe DNA into RNA, then synthesize proteins||Can bypass the stage when DNA transcribes into RNA|