Naked Science Forum
Life Sciences => Cells, Microbes & Viruses => Topic started by: Seany on 05/01/2009 23:16:07
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I understand that bacteria has a nucleus, whilst a virus doesn't.. But viruses still multiply themselves and seems to have a want to live. Surely that makes them a living thing?
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We were taught that all living things could do MRS.(C).GREN which stands for movement, respiration, sense, circulation (although that one is a bit dodgy), growth, reproduce, excrete, and nutrition (or something along those lines). I'm fairly sure that viruses can only carry out two of those functions, if my memory is correct. [::)]
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I do see your point.
Viruses
Move -- yes
Respire? -- (No. Viruses do not have the ability to respire on their own. They need to use the mitochondria of their host cells in order to use the process of respiration of the cell they have invaded. So, in other words,you could say that viruses "borrow" the respiratory ability of a cell, and that can be aerobic or anerobic, with or without oxygen.)
Sense -- no
Circulation -- no
Growth -- yes
Reproduce -- yes? multiplying in a way..
Excrete -- No idea..
Nutrition -- Surely they eat on something??
I'm still not sure whether MRS GREN has to agree for it to be living..! It's very vague!
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Bacteria are considered a living organism since it contains a cell (single) to survive on its own body and reproduce. A virus on the other hand is dependent on a host cell to survive and reproduce.
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Just like liver fluke or a whole raft of complex living organisms.
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It's an interesting definition- life is notoriously complex so it's no shock that it's hard to define.
The given definition excludes humans (among many others).
A human can't reproduce.
(It takes two- as the song goes).
Viruses
Move -- yes
No, not really.
They get moved by other things, but they can not move themselves- except in a very limited way. Some actively move their genetic material into the cell they infect.
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In recent years, we have found DOUBLE(probably more) the amount of life on this planet. These are the lifeforms that predator bacteria and viruses. They are classified as life.
We are just beginning to crack this new discovery. There is probably much more biomass in the planet, than on the planet.
And some now suspect many more lifeforms on a super small scale. It's quite puzzling.
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A virus on the other hand is dependent on a host cell to survive and reproduce.
This definition also excludes humans, since we depend on a biosphere (or a spacecraft/submarine) to metabolize, grow and reproduce.
- In reality, all life is interdependent, they just differ in degree
Some other definitions of life emphasize the copying of genetic information into new individuals
- which viruses do, in the right environment (like a cell)
- which humans also do, in the right environment (like a hotel)
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In recent years, we have found DOUBLE(probably more) the amount of life on this planet. These are the lifeforms that predator bacteria and viruses. They are classified as life.
We are just beginning to crack this new discovery. There is probably much more biomass in the planet, than on the planet.
And some now suspect many more lifeforms on a super small scale. It's quite puzzling.
https://oceanexplorer.noaa.gov/facts/marinemicrobes.html
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It's been awhile since I checked, but if I recall, this was found by environmental DNA assays. And some of the critters can not survive a lab environment.....or even be found yet. They assayed everything. Air, water, ice, soil, rock, oceans.
The last I heard, they were trying to establish the entity between the living and the non-living. With not too much luck.
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Bacteria are cells. Some are pathogens (harmful) while some actually help us (such as the ones in our stomach that help us digest food). Viruses are capable of attacking our body cells and bacteria. They are both living things. Nonliving things do not reproduce, do not feed themselves in order to grow or thrive, and does not use energy (e.g. rocks, dead leaves, etc.)
Viruses and bacteria are alive.
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All the things we classify as living, transpire water in some way. Viruses don't.
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Nonliving things do not reproduce, do not feed themselves in order to grow or thrive, and does not use energy
This guy
https://en.wikipedia.org/wiki/Wendell_Meredith_Stanley
was the first person to produce a crystal of a virus (the tobacco mosaic virus).
You can't crystallise something which is reproducing, feeding or using energy.
So it's clear that viruses don't do those things.
So they are not alive
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Yes but....people have grown wheat from 5000-year-old seeds found in the pyramids. Not much to choose between crystalline TMV which reproduces when introduced to its favored host, and wheat that does nothing for centuries and germinates as soon as it is wet. Indeed there is a vault of seeds being preserved in "crystalline" conditions just in case anyone survives the next nuclear war and can remember the code to the door in Svalbard. Is a wheat seed dead or live?
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Viruses possess some characteristics of life, it makes sense to call them alive in some cotexts eg they don't want to kill their host before the host can transmit them to a new host. Perhaps it was after the discovery of prions that scientists decided that theyhad to draw a line somewhere.
Sense, you could make a case for viruses being able to sense things.
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Perhaps it was after the discovery of prions that scientists decided that theyhad to draw a line somewhere.
It goes back a lot further than that. Trouble is the line can be difficult to define.
For example, would you say a virus senses its target cell and moves in, or does it randomly bump into things until it’s coating sticks?
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My priest tells me one human and the holy ghost is sufficient
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This topic gets complicated fast. Now, we might say that viruses are just chemical packets, but packets of chemicals don't encode for themselves... On the other side, they need life to do the trick. (Which makes me think about one thing - could a virus theoretically be replicated without using a cell?)
But wait, it gets more confusing. We have viruses that have a DNA count and some genes that are close to what we consider "life" and on the other side we have bacteria that hide in cells and replicate in them.
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If a virus has a DNA double spiral then surely it is alive and can mutate. If we freeze it can survive.
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If a virus has a DNA double spiral then surely it is alive
No.
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If a virus has a DNA double spiral then surely it ... can mutate
Yes, some viruses have their genetic material stored as double-stranded DNA, but other viruses use single-stranded DNA, and many have RNA (mostly single-strand, but some use double-stranded RNA).
https://en.wikipedia.org/wiki/DNA_virus
https://en.wikipedia.org/wiki/RNA_virus
Viruses can mutate, which means they can evolve - but just because they can mutate does not make them alive. They need to have a living host that can provide most of the cellular equipment to manufacture proteins and copy genetic material in order to replicate the virus.
Back when I was at school, the official view was that viruses were not alive. But viruses are on the edge of being alive - they have some properties of living things, but not others, so I can see why different people could come to different conclusions.
The discovery of some giant marine viruses with a physical size and genome size approaching some bacteria have further blurred the distinctions.
https://en.wikipedia.org/wiki/Pandoravirus
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What is the dividing line between living and nonliving?
I think the answer is simple, but not very satisfying. There is no line, just a fuzzy area between the 2.
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A bacterium, on its own, can reproduce; a virus, on its own, can't.
That's not very blurred.
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A bacterium, on its own, can reproduce; a virus, on its own, can't.
That's not very blurred.
But a virus can reproduce, it can be killed and it has DNA or RNA. Just seems kind of fuzzy to me...
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But a virus can reproduce
No, it can not.
No matter how long you sit and watch one, it will not reproduce.
it can be killed
No, it can not; that's why you see scientists talking about hand gel "inactivating" the virus.
it has DNA or RNA.
If it was cheap. I could use DNA to glue sawdust together to make chipboard, but it wouldn't be alive.
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A bacterium, on its own, can reproduce; a virus, on its own, can't.
A bacterium, by itself, will starve and/or boil, freeze, or explode.
- A bacterium needs a certain environment, including temperature, pressure, and a variety of organic compounds (mostly produced by other living bacteria).
- That's why bacteria like to live in a microbiome, as they all interact with each other, and produce things that others need
- That's why we can't grow around 95% of bacteria in the lab, because they are not self-sufficient - they depend on other living organisms to survive and thrive.
Similarly, a virus needs a microbiome to survice - and that environment includes its viral host
- I understand that the human microbiome has many viruses to keep it under control - if some particular microbe starts to take over, then bacteriophages targeting that microbe start to multiply, to keep it under control.
- It's when we "nuke" our microbiome with unnecessary antibiotics that some bacteria have no competition from other bacteria, and things can get really out of kilter...
Infection of a human is the common cold's method of reproduction...
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A bacterium, by itself, will starve and/or boil, freeze, or explode.
A bacterium in a Petri dish will do just fine.
But a virus won't do anything unless you add life.
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A bacterium, on its own, can reproduce; a virus, on its own, can't.
That's not very blurred.
I checked and apparently the majority of the biologists say that viruses are not alive. When it comes to subjects I am not well versed in a go with the experts so I now agree that viruses are not alive (I still wonder though...)
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A bacterium in a Petri dish will do just fine.
I understand that around 95% of bacteria "species" in a Petri dish will not grow, no matter what mix of food molecules, trace minerals, vitamins etc they are fed.
- That's because they naturally live in a microbiome, as a community of bacteria with networks of food/waste processing and even signaling paths.
- That's why so-called pro-biotics are a bit of a joke, because they only contain the small fraction of gut microbes that can be grown in a Petri Dish (and scaled up to a large-scale fermenter vat).
- That's also one reason why finding new antibiotics has been a challenge - some interesting bacterial candidates have been found, and their genomes sequenced. But they can't be grown as a monoculture - something that is almost demanded by the medical approval authorities.
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All that shows is that for 95% or bugs, we have not yet identified their "vitamins".
People with pernicious anaemia didn't need to eat raw liver, they needed to eat vitamin B12.