Science
22 Dec 08
26 Dec 08
Originally posted by divegeesterWhy have you asked this question? Bacterial, plant and fungal cells have an outer cell wall. Animal cells do not - they have an outer phospolipid membrane and that is all.
"Animals don't have cell walls" You sure about that?
So, I am intrigued by your question. PLease explain.
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27 Dec 08
Originally posted by znshoNo reason; I was thinking of membranes not walls, sorry.
Why have you asked this question? Bacterial, plant and fungal cells have an outer cell wall. Animal cells do not - they have an outer phospolipid membrane and that is all.
So, I am intrigued by your question. PLease explain.
27 Dec 08
1 edit
Originally posted by PBE6For all intents and purposes a virus is a dead or static organic structure
[b]The reason why a virus is not considered alive, is because it's not.
You have been misinformed. There is currently a debate in the scientific community about whether viruses are living or non-living.
There's a reason why computer viruses are called... well, viruses.
Yes, there is. It's because they model viral behaviour, not simply beca ...[text shortened]... pers to commit suicide in order for it to procreate:
http://en.wikipedia.org/wiki/Hairworm[/b]
when outside a suitable, living host cell (apparently it's referred to as a
virion then). I couldn't find anything to suggest that this is currently
being debated in the scientific community, but please post links
suggesting otherwise. Isn't the debate rather if the virus can be
considered alive once it's entered a suitable host cell due to the fact that
it may then reproduce itself and even react to changes in its surrounding
environment to some extent?
In any case, the analogy with the computer virus I think was to illustrate
how completely inert the virus is without the complimentary host cell.
Usually, when we think of parasites, we think of single-cell or multi-
cellular (viruses are non-cellular) organisms that require a host
only for nutrition, or as a suitable environment for reproduction. In all
other aspects they're independent of their hosts with their own internal
biological processes. A virus is the only "parasitic entity" I've heard of
that actually require its host to even "start working" at all.
So, my own conclusion is that the virus is like an encoded structure that
"comes to life (in the most basic sense of the word)" only when it's part
of a bigger system that can run its structure. (Yes, yes, as a
programmer I tend to view everything in this light; from this
perspective.)
Addition: I think maybe the best way to describe a virus, is that
it's an incomplete structure in terms of living organisms. It requires
more than itself to "come to life".
28 Dec 08
The newly identified "giant" virus, mimivirus is very interesting for many reasons, principally it's large size (min. ~400 nm) and huge genome (1.2Mbp, the biggest known to science) which is actually larger than the lower size range for bacteria and dwarfs the vast majority of other viruses.
The bigger end of the "normal" viruses like HIV-1, by comparison, are about ~120nm and about 10kb in size whereas smaller viruses like picornaviruses (enteroviruses etc.) are typically only about 20nm (~7kb).
Mimi- was actually thought to be a bacterium when Gram stained after first being found in a water cooler tower in Yorkshire during work into sourcing an agent implicated in an Legionella outbreak in a hospital (Bradford coccus).
http://en.wikipedia.org/wiki/Mimivirus
http://www.mcb.uct.ac.za/tutorial/mcb3011s/mg18925441.400-half-virus-half-beast--its-a-20sided-freak.html
As you know viruses do not encode all of the ribosomal rRNAs and other protein translation machinery to be able to replicate outside cells and though mimi- has an astounding repertoire in it's genome, even encoding tRNAs and other very complex biochemicals, it still appears to require a host amoeba to replicate.
The characteristics of life taught in school are feeding, excretion, respiration, movement (tropism), sensitivity, growth, reproduction and possession of nucleic acids, however, the concept of homeostasis is the key trait of a life form. That is a self-regulating, far-from-equilibrium, open thermodynamic system. Death is essentially the opposite of this.
http://www.scribd.com/doc/8147495/Notes-on-Equilibrium-Variants-of-Life
http://en.wikipedia.org/wiki/Ilya_Prigogine
04 Jan 09
Originally posted by AThousandYoungWhat kind of party was this? Is that what passes for a party in your parts? Do you see these people often? Why?
I was at a party last night and my wisdom was sought. I was asked three questions that I had a hard time with when I got put on the spot.
#1: What is the definition of "life"? How come viruses aren't alive? If you say it has to "live on it's own" then what about parasites, and the fact that most life needs to feed on other life?
#2: What's the ...[text shortened]... new questions for me, but I had a hard time giving answers. What are the right answers?
04 Jan 09
Originally posted by PBE6I'll admit I haven't read both links in their entirety, only the first few
http://www.sciam.com/article.cfm?id=are-viruses-alive-2004
http://www.wi.mit.edu/programs/ask/100206.html
pages of the first one, but it seems to confirm pretty much what I've
said.
Man, I must be stupid or something, 'cause I know you're not. Yet, you
seem to be implying that I'm basically wrong. 😕
Well, I'll just tip-toe back out of the science forum 'cause clearly this is
not the place for me. LOL! Nothing to see here. I'll be gone now. Spread
confusion somewhere else.
🙂
05 Jan 09
Originally posted by JigtieThat explains it. The first paragraph on p.3 of the first article discusses the Mimivirus, apparently the largest virus known. Here's a quote from the article:
I'll admit I haven't read both links in their entirety, only the first few
pages of the first one, but it seems to confirm pretty much what I've
said.
Man, I must be stupid or something, 'cause I know you're not. Yet, you
seem to be implying that I'm basically wrong. 😕
Well, I'll just tip-toe back out of the science forum 'cause clearly this is ...[text shortened]... e. LOL! Nothing to see here. I'll be gone now. Spread
confusion somewhere else.
🙂
As the research team noted in its report in the journal Science, the enormous complexity of the Mimivirus’s genetic complement “challenges the established frontier between viruses and parasitic cellular organisms.”
http://www.sciam.com/article.cfm?id=are-viruses-alive-2004&page=3
There's is also a nice bit on p.2 where the discuss the idea of a continuum 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.
http://www.sciam.com/article.cfm?id=are-viruses-alive-2004&page=2
The interesting part for me is the idea of the continuum of life. At present, there is no universal definition of "life". There is a conventional definition, but it's not as rigid as one would expect, with the consensus being "that life is a characteristic of organisms that exhibit all or most of the following phenomena:" which are listed as homeostasis, organization, metabolism, growth, adaptation, response to stimuli, and reproduction.
http://en.wikipedia.org/wiki/Life#Definitions
However, if there's no strict definition of life, then how can organisms be definitely classified? As mentioned by you and others elsewhere in this thread, traditionally viruses are not considered alive while bacteria are (since 1935, according to the first article), although bacteria like Rickettsia and Chlamydia and the Mimivirus blur the lines:
http://en.wikipedia.org/wiki/Rickettsia
http://en.wikipedia.org/wiki/Chlamydia_(bacterium)
http://en.wikipedia.org/wiki/Mimivirus
I suppose the debate really isn't about whether viruses are living or non-living in a dichotomic sense, but about whether a sharp dividing line between living and non-living things even makes sense.
07 Jan 09
Originally posted by AThousandYoungI view 'Life' as a property of patterns.
I was at a party last night and my wisdom was sought. I was asked three questions that I had a hard time with when I got put on the spot.
#1: What is the definition of "life"? How come viruses aren't alive? If you say it has to "live on it's own" then what about parasites, and the fact that most life needs to feed on other life?
#2: What's the ...[text shortened]... new questions for me, but I had a hard time giving answers. What are the right answers?
We find that matter is arranged into classes of patterns like 'rock', 'tree', 'human', 'virus'. Some patterns can self-replicate, that is, throw off more-or-less faithful copies of themselves under some conditions. Some patterns cannot. Those that can self-replicate, I would classify as alive.
Of course, the debate comes then about metabolism, sterility, etc. Is a mule not alive, because it is sterile? Well, look at the cells in a mule's body. They self-replicate, even if the animal as a whole does not. So since all the cells of a mule are alive, we could say that the animal is living -- even though as a whole organism it is in some sense dead because it will never have offspring.
I think the main difficulty comes in when we start to try to make decisions about granting rights to "living" things, and are reluctant to declare anything "dead" just because it is not replicating. For example, post-menopausal women would not wish to be classified as dead. Again, I would say they are alive because they consist of living cells.
On another tack, I view the computer virus as the first living organism created by man.
An interesting article for your students to read would be "The Microbotic Revolution" by Ian Stewart that appeared in the August 1981 issue of Omni magazine.
08 Jan 09
Originally posted by AThousandYoungThese are not things you think about every day so naturally you had to put some thought into the answer. That doesn't mean you don't know the answer.
I was at a party last night and my wisdom was sought. I was asked three questions that I had a hard time with when I got put on the spot.
#1: What is the definition of "life"? How come viruses aren't alive? If you say it has to "live on it's own" then what about parasites, and the fact that most life needs to feed on other life?
#2: What's the ...[text shortened]... new questions for me, but I had a hard time giving answers. What are the right answers?
I'm not sure I could come up with an accurate answer either.
#2 question I would answer off the top of my head as: Fungus propogate asexually and animals propogate sexually. 😀
08 Jan 09
Originally posted by AThousandYoungFonk dat! You need to hang out with a different crowd.
I was at a party last night and my wisdom was sought. I was asked three questions that I had a hard time with when I got put on the spot.
#1: What is the definition of "life"? How come viruses aren't alive? If you say it has to "live on it's own" then what about parasites, and the fact that most life needs to feed on other life?
#2: What's the ...[text shortened]... new questions for me, but I had a hard time giving answers. What are the right answers?
10 Jan 09
Originally posted by kirksey957Thread 105971
Fonk dat! You need to hang out with a different crowd.
12 Jan 09
Originally posted by AThousandYounglife is something you need to get.
I was at a party last night and my wisdom was sought. I was asked three questions that I had a hard time with when I got put on the spot.
#1: What is the definition of "life"? How come viruses aren't alive? If you say it has to "live on it's own" then what about parasites, and the fact that most life needs to feed on other life?
#2: What's the ...[text shortened]... new questions for me, but I had a hard time giving answers. What are the right answers?
fungus descended directly from fungus-protist, while animal descended from protozoa.
retrovirus is any virus that defies the Central Dogma.
I'm a Grade-A student at an University.
16 Jan 09
1 edit
Originally posted by PBE6I agree with the analogy that a neuron by itself (for instance) is not a
That explains it. The first paragraph on p.3 of the first article discusses the Mimivirus, apparently the largest virus known. Here's a quote from the article:
As the research team noted in its report in the journal Science, the enormous complexity of the Mimivirus’s genetic complement “challenges the established frontier between viruses and parasitic cell whether a sharp dividing line between living and non-living things even makes sense.
living thing but when part of the entire brain structure it's not imputable
to me that it serves an important role in the brain coming to life. I
suppose it's fair to say that a virus verge on life because of its
nearly-there state. Perhaps you're also right about the question itself
being purely academic, and the really interesting question is how much
of an impact viruses has really had on evolution and life itself.
I just read an article about how viruses can be used to revert adult cells
into embryonic stem-cell-like states. Remarkable! Anyone who would say
that viruses (alive or not) lack significance from an evolutionary or
biological perspective should consider the contents of this article:
http://www.sciencedaily.com/releases/2008/12/081215184343.htm
With the ability to drastically change the function and behaviour of a cell,
it's clearly not an inert, inconsequential structure once inside a suitable
cell. I still have a hard time accepting them as living things in
themselves, though. But that may just be me bonehead.