‘Are viruses living or non-living?’ This has been a contentious topic in the scientific world.
Actually, the answer to this question depends on what we consider living or how we define living. Viruses express characters of both living and non-living things; hence, they are somewhere in between the realm of living and non-living. A virus is not even considered as a cell or a microorganism; it is often defined as an acellular particle.
Viruses are obligatory parasitic infectious particles possessing only one type of nucleic acid and requiring the host cell’s mechanism to replicate. Viruses can infect all life forms – Archaea, Bacteria, and Eukarya. They are ubiquitous in nature and are the most abundant, diverse, adapted, and oldest biological entities in the world. Many viral strains are believed to have seen all the eons and epochs. They have infected the very first living cells, the Jurassic dinosaurs, and are still infecting current life forms.
Biologists claim viruses to be a borderline between chemistry and life or between living and non-living. Viruses contain some structures and phenomena displayed by organic life form but lack many others, including basic structural components and biosynthetic machinery characterizing a living entity. When outside the host’s cell, they do not show any sign of biological activities and can be defined as organic particles made of nucleic acid and protein. However, when in contact with a suitable host, they become active and start showing a fundamental biological trait – replication and transformation of genetic information to future generations.
Some living and non-living traits of viruses are listed below:
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Two (2) Living Characteristics of Viruses
Viruses possess two traits of living things, i.e., the capacity to reproduce and the presence of nucleic acid. They can spread from one host’s cell or body to another, cause host disease, and increase their number. Hence, some believe viruses to be alive because they have been present since billions of years ago, have transferred their genetic materials to their progenies, and continue to exist to this date, experiencing several mutations and adaptive alternations.
1. Reproduction
Viruses can multiply and increase their number using the host cell’s machinery, like the host’s nucleic acids and ribosomes.
2. Presence of Nucleic Acid
Viruses contain either DNA or RNA, but never both, as their genome. As such, they can transfer the genetic information from one generation to another.
They also suffer from mutation and evolution phenomena. Causing mutation in their proteins, viruses can adapt to the host’s changing environment.
Six (6) Non-living Characteristics of Viruses
Despite their capacity to replicate or change their genome, viruses do not bear any other traits of a living being. Even the reproduction, as it is seen, is not autonomous – it is totally dependent on the host’s nucleic acid and protein synthesizing machinery.
1. Lack of Cellular Organization (Are Acellular)
Viruses lack protoplasm, cell organelles, and other cellular components. The viral genome and proteins covering the viral genome are only the components of a virus; even the viral envelopes are made of the host’s cell membrane.
2. Lack Metabolic Machinery
Viruses do not have respiratory mechanisms and are not able to produce their energy own energy. In fact, they depend on the host for energy required for processes like viral replication. No, any anabolic or catabolic reactions occur within viruses.
3. Lack Autonomous Reproduction
Though viruses can multiply, they can’t do it on their own. They need the host cell’s nucleic acids, the host’s transcription, translation, and transformation mechanisms, and the host’s cellular physiologies to replicate their own genome, produce their proteinaceous coat and assemble viral components.
4. Do not Grow
Viruses do not grow in size and complexity at all.
5. Lack of Response to Stimuli
As with other living entities, viruses are immune to stimuli. They do not show any reflexes or responses against environmental stimuli like light, sound, temperature, etc. However, it doesn’t mean that they are immune to changes in environmental physical or chemical state. Their makeup may disintegrate when their environment is altered physically or chemically beyond a limit.
6. Can be Crystallized
Viruses can be crystallized into an organized solid structure using rigorous scientific processes.
Conclusion
Based on the current understanding and definition of life, claiming viruses as alive or dead objects is impossible. It must be considered in between non-living complex molecular organization and simple biological entity- a border between living and non-living.
References
- Koonin, E. V., & Starokadomskyy, P. (2016). Are viruses alive? The replicator paradigm sheds decisive light on an old but misguided question. Studies in History and Philosophy of Biological and Biomedical Sciences, 59, 125. https://doi.org/10.1016/j.shpsc.2016.02.016
- https://microbiologysociety.org/publication/past-issues/what-is-life/article/are-viruses-alive-what-is-life.html
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- Gortner, R. A. (1938). Viruses—Living or Non-Living? Science. https://doi.org/529
- https://serc.carleton.edu/microbelife/yellowstone/viruslive.html
- https://edubirdie.com/examples/are-viruses-living-or-non-living/
- https://www.bottomscience.com/are-viruses-living-or-non-living/
- https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(Kaiser)/Unit_4%3A_Eukaryotic_Microorganisms_and_Viruses/10%3A_Viruses/10.01%3A_General_Characteristics_of_Viruses
- https://biologyteach.com/virus-living-and-non-living-characters/
- https://www.biology.lifeeasy.org/8434/living-and-nonliving-characteristics-of-viruses
