Posts Tagged ‘life’

If a virus is not alive, how does it die?

March 24, 2020

You can’t strictly kill a virus since it is not alive.

Outside living cells, some viruses remain potentially active for thousands of years. A virus recovered from permafrost was able to infect an amoeba. Influenza and corona viruses are thought to stay active for a few hours or days. But the smallpox virus can remain active for years

These days there are many reports about how long the coronavirus remains “alive” or “viable” or “active” on surfaces.  For example this is an abstract of a new paper (yet to be published):

Aerosol and surface stability of HCoV-19 (SARS-CoV-2) compared to SARS-CoV-1

Abstract
HCoV-19 (SARS-2) has caused >88,000 reported illnesses with a current case-fatality ratio of ~2%. Here, we investigate the stability of viable HCoV-19 on surfaces and in aerosols in comparison with SARS35 CoV-1. Overall, stability is very similar between HCoV-19 and SARS-CoV-1. We found that viable virus could be detected in aerosols up to 3 hours post aerosolization, up to 4 hours on copper, up to 24 hours on cardboard and up to 2-3 days on plastic and stainless steel. HCoV-19 and SARS-CoV-1 exhibited similar half-lives in aerosols, with median estimates around 2.7 hours. Both viruses show relatively long viability on stainless steel and polypropylene compared to copper or cardboard: the median half-life estimate for HCoV-19 is around 13 hours on steel and around 16 hours on polypropylene. Our results indicate that aerosol and fomite transmission of HCoV-19 is plausible, as the virus can remain viable in aerosols for multiple hours and on surfaces up to days.

But then I also read that viruses are not “alive”. They are just a bunch of chemicals, non-bacterial pathogens,  which, by unknown mechanisms, just happen to have

  1. long molecules of DNA or RNA that encode the structure of the proteins by which the virus acts;
  2. a protein coat, the capsid, which surrounds and protects the genetic material; and
  3. in some cases an outside envelope of lipids

Scientific American:

For about 100 years, the scientific community has repeatedly changed its collective mind over what viruses are. First seen as poisons, then as life-forms, then biological chemicals, viruses today are thought of as being in a gray area between living and nonliving: they cannot replicate on their own but can do so in truly living cells and can also affect the behavior of their hosts profoundly. The categorization of viruses as nonliving during much of the modern era of biological science has had an unintended consequence: it has led most researchers to ignore viruses in the study of evolution. Finally, however, scientists are beginning to appreciate viruses as fundamental players in the history of life. …..

What exactly defines “life?” A precise scientific definition of life is an elusive thing, but most observers would agree that life includes certain qualities in addition to an ability to replicate. For example, a living entity is in a state bounded by birth and death. Living organisms also are thought to require a degree of biochemical autonomy, carrying on the metabolic activities that produce the molecules and energy needed to sustain the organism. This level of autonomy is essential to most definitions.

Viruses, however, parasitize essentially all biomolecular aspects of life. That is, they depend on the host cell for the raw materials and energy necessary for nucleic acid synthesis, protein synthesis, processing and transport, and all other biochemical activities that allow the virus to multiply and spread. One might then conclude that even though these processes come under viral direction, viruses are simply nonliving parasites of living metabolic systems. But a spectrum may exist between what is certainly alive and what is not.

A rock is not alive. A metabolically active sack, devoid of genetic material and the potential for propagation, is also not alive. A bacterium, though, is alive. Although it is a single cell, it can generate energy and the molecules needed to sustain itself, and it can reproduce. But what about a seed? A seed might not be considered alive. Yet it has a potential for life, and it may be destroyed. In this regard, viruses resemble seeds more than they do live cells. They have a certain potential, which can be snuffed out, but they do not attain the more autonomous state of life. Another way to think about life is as an emergent property of a collection of certain nonliving things. Both life and consciousness are examples of emergent complex systems. They each require a critical level of complexity or interaction to achieve their respective states. A neuron by itself, or even in a network of nerves, is not conscious—whole brain complexity is needed. Yet even an intact human brain can be biologically alive but incapable of consciousness, or “brain-dead.” Similarly, neither cellular nor viral individual genes or proteins are by themselves alive. The enucleated cell is akin to the state of being braindead, in that it lacks a full critical complexity. A virus, too, fails to reach a critical complexity. So life itself is an emergent, complex state, but it is made from the same fundamental, physical building blocks that constitute a virus. Approached from this perspective, viruses, though not fully alive, may be thought of as being more than inert matter: they verge on life.

But how then do they die? Clearly there has to be a chemical change. Is it just a case of going from active to inactive as chemistry changes?

And that begs the question as to what that chemical change might be.


 

Life exists as a succession of identities

November 18, 2017

Life is an abstract concept manifested as living things. The thread of life has no discernible beginning.

Life – to be life – must be manifested in an entity capable of reproduction. The elements displaying life either continue or come to an end. The thread is carried as a possibility by every sperm and every egg but the sperm and egg cannot themselves reproduce. Most of these possibilities come to an end before the two combine. If – and only if – a sperm and egg do combine, then life continues as, and within, a unique identity created by that combination. It is the creation of the identity – at conception – which continues life. About one in 300 billion sperm survives to combine with about one in 200 eggs to create an identity. It is a unique genetic identity. That identity, first as a fetus may end before birth. Or it may continue after birth as a child. It may grow to be an adult human and give rise to further sperm or eggs before itself coming to an end. When that identity qualifies to be considered a human entity and protected by society is a choice for the societies and the individuals concerned. Most societies start assigning the identity some rights and protections before birth but only after about 20 weeks of life as a fetus.

There is little doubt, however, that a unique genetic identity is created at conception, whether in a test tube or in a womb. At what stage of development that identity achieves consciousness and then self-awareness is not certain but almost certainly only after a rudimentary brain has formed. That would be some weeks after conception but probably some little time before birth. At what point that identity is to be afforded legal “rights” is then a matter for the surrounding society to determine.

Until the identity reaches birth – whether by natural or by artificial means – it has no options and no choices to exercise. Whether self-aware or not, its existence is in the gift and the power of others. It starts acquiring choices and freedoms of action only after birth, as allowed or constrained by its own development and the rules of the society it finds itself in.

Life then only exists as a succession of identities.

To trace the beginning of life would require going back from identity to identity to the specific cells some 3.7 billion years ago. A collection of sperm and eggs may contain the elements for life to continue but do not in themselves constitute life. The beginning of an identity is not the beginning of life. But the act of conception brings a unique identity into being and it is surely the beginning of a specific new life.

Life may be continuous as a concept but can only be realised and manifested as a succession of unique, discrete identities.


 

When is a strawberry dead?

June 25, 2013

An interesting discussion yesterday on BBC Radio

What Is Death?

Series 8 Episode 1 of 6 Monday 24 June 2013

“What Is Death?”

In the first of a new series of the award winning science/comedy series, Brian Cox and Robin Ince are joined on stage by comedian Katy Brand, biochemist Nick Lane and forensic anthropologist Sue Black to discuss why death is such an inevitable feature of a living planet. As well as revisiting such weighty scientific issues, such as when can a strawberry, be truly declared to be dead, they’ll also explore the scientific process of death, its evolutionary purpose and whether it is scientifically possibly to avoid it all together.

The death of a strawberry had apparently been discussed on an earlier program last year:

Brian Cox Strawberry

A fascinating discussion regarding when a cell can be truly considered “dead” though I couldn’t quite agree that death was necessary to evolution. Only birth is of course. It would be pretty crowded without death but life – or death – after procreation no longer has any part to play in the passing on of genes to the next generation or on evolution. With immortality there would, of course, be no need for procreation or for any future generations. But if immortal beings did beget other immortal beings then an Infinite Universe would come in very handy. However, the fertility rate needed for replenishment of the mortal members of a species is unconnected to the longevity of the individuals and I cannot see that death, per se, has any impact on evolution.

As far as the life and death of a strawberry are concerned it seemed to me that the question was essentially meaningless. You could as well ask if your finger could be alive when it no longer was connected to your body. A finger -like a strawberry is never truly alive unless connected to the body that it is a part of and the question of life or death when it is separated from its host body is moot.

Self-replicating fingers – or strawberries – would make John Wyndham’s Triffids seem benign.


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