Virus living or nonliving thing

In viruses, none of these are active processes, they simply occur based on the virus's chemical make-up and the environment in which it ends up. When scientists apply this list of criteria to determine if a virus is alive, the answer remains unclear. Because of this, the debate of whether viruses are living or non-living continues. As the understanding of viruses continues to develop, scientists may eventually reach a final decision on this question. No matter what side of the debate you might be on, we know that viruses can be deactivated.

Once they are inactive, they cannot infect a host cell. There are two types of viruses, those with a lipid, or fatty outer shell and those that have a protein coating called a capsid. For the viruses that have a lipid shell you can use common soap to basically tear apart the outer coating and deactivate the virus.

The remaining parts can then be washed down the sink and are harmless. The great thing about this is it only takes about 20 seconds of thorough hand washing with soap and water to do this. Viruses with protein coatings like the rhinoviruses and adenoviruses that cause the common cold are not deactivated by soap, but are still dislodged from our skin and surfaces so that they can be washed down the sink. This is also why washing your hands with soap and water is better than using a hand sanitizer.

Hand sanitizers do not have the same effect of removing the viruses from our skin so they can be washed down the sink. While we know many of you came to this page to find out whether viruses are alive or not, we've also been receiving many follow-up questions about the Coronavirus.

Here are some resources we think may be helpful:. One of the most up-to-date Coronavirus case maps showing the numbers of confirmed cases across the globe and split into counties within the US , from the University of Virginia. For how to respond and how to act, visit the WHO's Coronavirus advice to the public. See how important masks and distancing are in slowing the spread in some areas. Immediately to the right of the quasi-replicators are viroids, arguably, the simplest bona fide replicators.

Typical group I self-splicing introns that encode endonucleases involved in the intron transposition and inteins can be considered protein-coding replicators with the lowest degree of autonomy. Both types of elements, in addition to the catalytic moieties required for self-splicing at the RNA and protein levels, respectively , encode homing endonucleases that enable transposition to homologous and less frequently to ectopic sites Mills, Johnson and Perler ; Nielsen ; Nielsen and Johansen ; Starokadomskii Chromosomes, the cellular replicators, that encode all proteins involved in replication and a much greater number of accessory with respect to replication proteins and structural RNAs occupy the opposite end of the spectrum which corresponds to the maximum autonomy Figure 1.

In between are all other diverse replicators including transposable elements, plasmids and viruses, as well as organelle genomes from mitochondria and chloroplasts Figure 1. The genomes of these non-cellular replicators span the range from about one kilobase small transposons and satellite viruses to over two megabase giant viruses and widely differ in terms of the complements of proteins they encode Koonin and Dolja , The only universal feature shared by all replicators is the presence of some signal that enables replicative autonomy.

That signal can consist solely of nucleotide sequences that are recognized by the host replicative apparatus as is the case in many bacteriophages e.

Many replicators with small genomes encode a single enzyme involved in replication such as the reverse transcriptase of retroelements, the replication initiator endonuclease-helicase of various rolling circle elements, and transposases recombinases of simple transposable elements Koonin and Dolja ; Koonin et al ; Kristensen et al ; Piegu et al Replicators with larger genomes encode multiple proteins that comprise the replication machinery that can reach high complexity, e.

An orthogonal dimension of the replicator universe spans the range of reproduction strategies or life styles , from complete selfishness associated with parasitism to full cooperativity self reliance Figure 1.

Lytic viruses that replicate rapidly and kill the infected host in the process are the epitome of selfishness whereas cellular life forms can be considered ultimate cooperators that serve as self-reliant hosts to the selfish replicators even though cellular life forms have evolved multiple layers of defense as discussed below.

All other classes of replicators fall in between these two extremes. Temperate viruses either reproduce at a limited rate without killing the host cell or switch between integrated lysogenic and lytic reproduction strategies Joh and Weitz ; Oppenheim et al Transposable elements propagate both within and together with the host genome at different paces that depend both on the intrinsic rates of replication and transposition, and by the interaction with the host defense mechanisms Piegu et al ; Wicker et al Plasmids replicate under more or less tight control from the host, with some reaching high copy number and others represented by a single or a few copies per cell.

Apart from the lytic viruses, all these replicators depend on the long-term survival of their respective host cells, the ultimate cooperators, and thus combine selfishness with cooperativity in different proportions as captured in the recent classification of replicators into 5 classes along the selfishness-cooperativity axis Jalasvuori ; Jalasvuori and Koonin Arguably, an inverse relationship between the degree of autonomy and selfishness could be expected: ultimate, most aggressive parasites would shed all the genetic material other than that required for replication under selection to maximize the replication rate whereas parasites involved in complex interactions with the host would retain a diversified set of genes.

Remarkably, however, there is at best a rough correspondence between autonomy, complexity and selfishness. For example, lytic viruses and virus-like agents that replicate rapidly and kill the host cell can have tiny genomes as is the case for viroids, RNA bacteriophages or some ssDNA viruses or large ones, exceeding in size those of many cellular life forms as in giant viruses. Conversely, inteins and self-splicing introns, which are among the smallest replicators, as well as megaplasmids with genomes on par with those of the largest viruses, in most cases are harmless for the host.

Obviously, replicators cannot reproduce in isolation. They require resources, such as nucleotides and amino acids, to build progeny genomes and devices for their reproduction that consist of proteins and RNA, as well as vehicles that facilitate the acquisition of the said resources and spread of the progeny Dawkins , ; Jalasvuori ; Jalasvuori and Koonin As with autonomy and selfishness see the preceding section , replicators span broad ranges of possibilities with respect to resource production and modification of the host metabolism, and the nature of the vehicles Figure 2.

However, unlike replicative autonomy and selfishness, the capabilities of replicators with respect to resources and the nature and complexity of the vehicle are coupled. The replicators are sharply divided into two major categories with respect to resource production: i producers that make all the resources required for replication or make some of the resources and actively import others in an energy-dependent manner, i. Arguably, as far as the resource autonomy is concerned, there is a sharp distinction between autonomous cellular life forms and non-autonomous selfish replicators.

Yet, as almost always is the case in biology, borderline situations exist. As in Figure 1 , the specific positions of different groups of replicators along the resource production axis is determined only qualitatively. However, on the vehicle axis, there are only three distinct positions for the two types of vehicles and the replicators without vehicles. The designations for the classes of replicators are as in Figure 1. While most of the producers cellular life forms make all of the energy they use and most if not all building blocks, some intracellular bacteria are energy parasites that obtain most if not all of their ATP from the host Moran ; Tamas et al Conversely, some of the non-producers, such as large viruses, encode some metabolic enzymes, e.

Among other processes, non-producers can contribute to energy conversion as is the case with cyanophages many of which encode cyanobacterial photosystems Clokie and Mann ; Thompson et al Furthermore, even small non-producing replicators, such as RNA viruses, affect modifications of the host cell metabolism and the formation of structures, such as virus factories, that channel substrates into viral genome replication Harak and Lohmann ; Romero-Brey and Bartenschlager All the prowess of viruses in the modulation of the host metabolism notwithstanding, producers and non-producers are clearly distinct: to the best of our current knowledge, non-producers never direct the formation of energizable membranes, extremely rarely encode complete metabolic pathways and never a complete translation system Koonin and Dolja ; Raoult and Forterre With regard to the vehicles, there are three distinct classes of replicators, those with: i no vehicles plasmids, transposons and other non-viral selfish elements , ii virus-vehicles virions , iii cell-vehicles Figure 2.

While the repertoire of genes and signals involved in replication defines the replicative autonomy of a replicator as discussed above, the type of vehicle determines a different dimension of autonomy that can be denoted biological or ecological.

The resident replicators of cell-vehicles enjoy full or at least partial in the case of parasites, symbionts and organelles biological autonomy whereas the vehicle-less replicators and replicators with virus-vehicles depend on the cell-vehicles. Yet, the degree of autonomy is quite different between the two classes of parasitic replicators as the virus-vehicles provide for the long-term survival of extra-cellular virions and effective means for infecting new cells.

Furthermore, the virions of many viruses, such as double-stranded RNA and negative-strand RNA viruses as well as retroviruses that package polymerases and other enzymes, are directly involved in the genome replication. The fundamental distinction between cell-vehicles and virus-vehicles treads the same line as the distinction between producers and non-producers. The cell vehicles are dynamic, metabolically active entities bounded by energizable membranes and often capable of active movement whereas the virus vehicles are essentially inert although many contain enzymes that are activated within the host cell vehicle.

Again, however, the boundary is not absolutely sharp, and the analogy between virions and bacterial spores an inert version of the cell-vehicle is hard to overlook. A network of evolutionary relationships exists between replicators without vehicles plasmids and various mobile elements and bona fide viruses Koonin and Dolja ; Koonin, Dolja and Krupovic Transitions from one type of replicators to another have occurred on numerous occasions in the course of evolution. In a sharp contrast, there is no evidence of evolutionary transitions between cells and viruses.

Claims to the contrary that have become rather popular in the wake of the discovery of giant viruses Claverie et al ; Claverie et al ; Colson et al ; Raoult et al are readily refutable by phylogenomic analysis Forterre et al ; Yutin et al On the contrary, most of the essential viral genes viral hallmark genes have no close homologs among genes of cellular life forms except for obvious cases of capture of viral genes by the hosts and accordingly are likely to have originated in a primordial, pre-cellular gene pool E.

Koonin, ; E. Thus, it is important to note that, whereas replicators form continua along the axes of selfishness-cooperativity and genome complexity, there is discontinuity when it comes to the vehicles and resource production Figure 2.

The discontinuity extends also to the major differences in the gene content of cellular genomes and the genomes of selfish elements. All of the former encode the complete machineries for translation and for the maintenance of energizable membranes whereas none of the selfish replicators do even if genes for some components of these machineries are present. Arguably, this gulf between cells and selfish replicators that reflects fundamentally different survival strategies is the deepest divide between classes of biological entities Koonin and Dolja Every biological system, such as a unicellular or multicellular organism, is a complex, interwoven community of replicators of different types Figure 3.

Indeed, all cells, with the possible exception of highly degraded intracellular parasites, carry multiple transposable elements; many cells also contain various plasmids; and all or nearly all cellular life forms are frequently attacked by viruses. The relationships between these diverse replicators span the range from mutualism to commensalism to antagonism.

For example, plasmids often form a mutualistic link with the resident cellular replicators chromosomes by providing essential metabolic capacities Petersen et al ; Stasiak et al or resistance to antibiotics Andersson and Hughes Prophages that are contained in most prokaryotic genomes can boost the host immunity to virus superinfection and apparently might provide other benefits such as stress resistance Paul ; Wang et al Moreover, a distinct class of defective prophages known as Gene Transfer Agents serve as dedicated vehicles for gene transfer between prokaryotes Lang et al The arrows denote both physical fusion integration and parasitic, commensal or symbiotic relationships between different classes of replicators.

Transposable elements generally should be considered commensals or even aggressive parasites of their cellular hosts. However, a large body of evidence indicates that sequences from these elements are routinely recruited as regulatory regions of host genes Jordan et al ; Makalowski ; Rebollo et al Less frequently but also on many occasions, entire genes of mobile elements are captured to function in the host cells Alzohairy et al ; Bowen and Jordan ; Rebollo, Romanish and Mager The telomerase, a key enzyme in the replication of eukaryotic linear chromosomes, that was derived from retroelements is one striking example Gladyshev and Arkhipova ; Koonin , and the much more recent capture of syncytins, essential placental proteins, from retroviruses is another Dupressoir et al Conversely, recruitment of genes from the cellular hosts, when viral genomes randomly captures host DNA that can be fixed in evolution if selected for a function beneficial to the virus, is a common route of evolution among viruses and other selfish replicators Filee and Chandler ; Filee et al ; Yutin and Koonin see more below on gene exchange between different classes of replicators.

Beyond gene exchange and recruitment, fusion of replicators or more precisely replicons, for this occasion is a ubiquitous phenomenon in all organisms McGeoch and Bell Obviously, this is an integral feature of the life cycles of transposable elements.

Numerous integrated elements lose their autonomy and degrade, ultimately beyond recognition, to become parts of the host genomes. Although not reaching such extravagant heights, amelioration of both transposable elements and proviruses is common also in bacteria and archaea. Moreover, analysis of archaeal genomes reveals multiple fossils of plasmids suggesting that plasmid accretion is a major path of genome evolution Iyer et al ; McGeoch and Bell Even for lytic viruses, data are accumulating on frequent integration into the host genomes, even if this process is spurious with respect to virus reproduction Chiba et al ; Koonin ; Liu et al A striking example of fusion between distinct parasitic replicators are the IStrons which are hybrids between Group I self-splicing introns and insertion sequences, and combine properties of introns and DNA transposons Tourasse et al Similarly, large DNA viruses often harbor self-splicing introns and serve as vehicles for their dissemination Edgell et al ; Yoosuf et al Apparently, genome fusion and integration along with interactions that do not involve physical joining connect all classes of replicators into a single network Figure 3.

The evolution of life is often described as an incessant arms race between hosts and parasites Forterre and Prangishvili , ; Koonin and Dolja ; Koonin and Krupovic b ; Koonin and Wolf Probably, a more accurate statement is that the entire history of life is a story of host-parasite coevolution. This cooperation is manifested not only in gene exchange as outlined above but also in self-constraining strategies of numerous selfish replicators. The arms race promotes evolution of multiple, intricate defense systems in all cellular life forms along with counter-defense systems in selfish replicators.

Defense of cellular life forms typically consists of multiple layers including resistance mechanisms such as rapid evolution of virus receptors , innate and often also adaptive immunity, and programmed cell death Flajnik and Du Pasquier ; Makarova et al ; Makarova et al ; Rimer et al Strikingly, adaptive immunity systems in archaea and bacteria the CRISPR-Cas systems and in animals appear to have evolved through recruitment of different transposable elements Koonin and Krupovic a , and a similar path of evolution led to the origin of an innate immunity system in ciliates Swart and Nowacki The finding that at least three distinct classes of transposons gave rise to three very different immunity systems implies a general principle whereby selfish replicators that are naturally evolved genome rearrangement devices are recruited for those defense mechanisms that involve such rearrangements Koonin and Krupovic b.

Counter-defense, i. Larger selfish replicators, such as viruses with large genomes, encompass numerous genes that encode multiple counter-defense mechanisms. Many if not most components of antidefense systems are recruited from the host defense although not all of them possess quasi-replicator properties Gewurz et al ; Ploegh ; Vossen et al We have discussed several axes on which replicators occupy different positions. Yet another one is the axis of replication efficiency vs environmental adaptation.

Any replicator faces the fundamental trade-off between maximizing the rate of replication as such and evolving adaptations to the respective environment that provide for maximization of the resource supply and genome protection.

In the case of selfish replicators, the adaptations largely include counter-defense systems. Replicators are extremely widely spread along this axis. The trade-off effectively amounts to the well-known dichotomy, in ecology and evolution, between r and K strategy where the r strategy involves maximization of the reproduction rate whereas the K strategy entails elaborate adaptation Hastings and Caswell ; Molenaar et al Generally, the r strategy wins in unstable, shifting environments that, however, provide plentiful resources for short time intervals, whereas the K strategy is advantageous in stable environment with limited resources Ponge Understanding in more specific terms how the fundamental choice between different evolutionary strategies is made, is key to the study of replicator coevolution and remains a major open research problem.

The coevolution of selfish and cooperative replicators appears to be a powerful driving force of evolution. Mathematical models of coevolution convincingly show that, in well-mixed populations of hosts, parasites cause collapse of the entire host-parasite system.

Stable coevolution is possible only in structured populations Takeuchi and Hogeweg , ; Takeuchi, Hogeweg and Koonin Thus, selfish replicators promote evolution of complexity of the entire replicator ecosystem. More specifically, such major evolutionary transitions as the advent of DNA as a dedicated information storage device Takeuchi, Hogeweg and Koonin and the origin of multicellular life forms could have been promoted by the parasite-host arms race, in particular, through the evolution of programmed cell death as a defense Iranzo et al Worse, any answer to this question does not seem to lead to any constructive developments.

In contrast, the status of viruses in the realm of biology is naturally defined within the framework of the replicator paradigm. In the continuum of replicators along the selfishness-cooperativity axis, lytic viruses represent the selfish extreme whereas other parasitic replicators span a broad range. Selfish replicators are not only a part of the biological world but constitute an intrinsic, central part of that world.

No replicator system can evolve without the emergence of parasites, and parasitic replicators drive the evolution of complexity at more than one level.

Originally published by Cosmos as Why are viruses considered non-living? Cosmos is published by The Royal Institution of Australia, a charity dedicated to connecting people with the world of science.

Financial contributions, however big or small, help us provide access to trusted science information at a time when the world needs it most. Please support us by making a donation or purchasing a subscription today. Share Tweet. Virus are not quite alive. More on:. Get an update of science stories delivered straight to your inbox. One theory on their origin is that viruses evolved from cells then branched out and evolved separately, backing the notion that they are indeed alive.

Studying the shapes of their proteins , for example, has shown that viruses share certain protein structures — and therefore properties — with organisms from all branches of the tree of life. There are variations to this theory, such as the idea that viruses might have come from circular pieces of DNA called plasmids in archaeans , and that giant viruses might be the remnants of extinct domains of life.

Ultimately, science may never agree on whether viruses are alive or not. The answer is not as straightforward as you may think. Articles Videos.