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Thread: Are Viruses Alive?????

  1. #1
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    Question Are Viruses Alive?????

    I've heard several different things on viruses some say that they are considered living organism, some say that they don't meet all the requirements of life and just attack and reside in cells, some say both. So my question is are viruses considered alive, do they meet all the requirements of life, and how do they live (if they do) in your body?
    "Love the Lord your God with all your heart and all your mind, and love your neighbor as your self, there are no two greater commandments than thes" - Jesus Christ God of the Universe.

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    From what I remember from the biology class I took a year or so ago, they are not alive. But, I'm no biology expert either. Come to think of it, I have had an interest in this. I should do some research myself.
    Truth gains more even by the errors of one who, with due study and preparation, thinks for himself, than by the true opinions of those who only hold them because they do not suffer themselves to think.
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  3. #3
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    I believe that viruses are not alive. They all got sick and died out.
    Seriously, I don't really know if they are alive or not. If I remember correctly, they are missing some "live" ingrediant that doesn't make them alive. But I last took Biology 6 years ago, and that kind of information always changes or at least has a high chance of changing with in that amount of time.
    Like an echo down a canyon, never coming back as clear; Lately I just judge the distance not the words I hear.
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  4. #4
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    I think its the lacking the machinery to replicate yourself aspect that generally disqualifies them, even if you use a much looser definition that includes early self replicating molecules.
    I'd class them as alive, seeing as they can take action to replicate themselves even they if don't possess the ability on their own (I can't replicate on my own either).

    Its not particularly important really though, at the boundaries 'life' is an arteficial concept that won;t really have much impact on anything anyway.

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    Quote Originally Posted by omega
    I've heard several different things on viruses some sa hat they are considered living organism, some say that they don't meet all the requirements of life and just attack and reside in cells, some say both. So my question is are viruses considered alive, do they meet all the requirements of life, and how do they live (if they do) in your body?
    They're not alive in the traditional meaning of the term. The problem is, the idea of alive/not alive took hold long before the discovery of viruses; and human brains are very reluctant to give up a nice, simple dichotomy.

    Viruses are what they are: packaged nucleic acid sequences that can invade and replicate themselves in specific host cells. They are not subservient to any human definition of what is and is not 'alive'.

  6. #6
    DamEtel Guest
    Here's something I wrote for my personal notes a few years ago. If I had time, I would expand on some of the fundamental characteristics' definitions/descriptions, but will let them stand as is for now.






    First, a brief introduction to “life” itself may be in order. For example, it is easy for a person to see a rock and a bird and determine which is living and which is not. But can that person pinpoint what it is about the bird that qualifies it as living? What exactly is it that distinguishes the realm of the living from that of the non-living? In a broad sense, there are basically four methods used to distinguish the animate from the inanimate.

    1) Cell Theory
    In the simplest terms, the cell theory states that anything composed of one or more (functioning) cells is living, and, anything that lacks cells is not.

    “As originally postulated by Schwann, the cell theory had two basic tenets:

    1. All organisms consist of one or more cells.

    2. The cell is the basic unit of structure for all organisms.

    Less than 20 years later, another tenet was added….

    3. All cells arise only from preexisting cells.

    Thus, the cell is not only the basic unit of structure for all organisms but also the basic unit of reproduction. In other words, all of life has a cellular basis.” (Wayne Becker, Jane Reece, Martin Poenie, The World of the Cell, Third Edition, Benjamin/Cummings Publishing Company, 1996, p4)
    “Two German scientists, botanist Matthias Schleiden in 1838 and zoologist Theodor Schwann in 1839, were the first to point out that all plants and animals are composed of cells. Later, Rudolph Virchow, a physician, observed cells dividing and giving rise to daughter cells. In 1855, Virchow
    proposed that new cells are formed only by the division of preexisting cells. In other words, cells do not arise by spontaneous generation from nonliving matter, a belief that had prevailed for centuries.

    The work of Schleiden, Schwann, and Virchow gave rise to the cell theory, the unifying concept that cells are the basic living units of organization and function in all organisms and that all cells from other cells.” (Eldra Pearl Solomon, Linda R. Berg, & Diana W. Martin, Biology: Fifth Edition, Saunders College Publishing, 1999, p74)
    “It is a remarkable fact that living forms, from amebas and unicellular algae to whales and giant redwood trees, are formed from a single type of building unit: the cell. All animals and plants are composed of cells and cell products. Thus the cell theory is another of the great unifying concepts
    of biology.” (Cleveland P. Hickman Jr., Larry S. Roberts, Allan Larson, Integrated Principles of Zoology, 10th Edition, McGraw –Hill, 1997, p42)
    “Theodor Schwann proposed the cell theory. This theory states that all organisms are composed of basic units called cells, which are derived from preexisting cells.” (William S. Klug, Michael R. Cummings, Concepts of Genetics, Fifth Edition, Prentice Hall, 1997, p4)


    2) Basic Characteristics of Life
    Another method used to determine whether something is animate or inanimate is to examine its properties. Since most forms of life share certain basic characteristics, if the object under consideration possesses most or all of these, it could be considered as living. Different sources list different characteristics, but some of the main ones are as follows.

    1. Responsiveness (Irritability) – Living organisms respond to stimuli and changes in their environment. For example, a cat or dog can be startled by a loud noise, a person can turn his/her head in response to a flash of light, plants grow towards light sources, and an ameba can stalk its prey by “sensing” its presence and location.

    2. Growth (Development) – Living organisms undergo a life cycle which includes growth and development. For example, a human zygote is a single fertilized cell out of which a complete, full-grown person will eventually develop. The zygote divides and as time passes, the number of cells increases as does the size of the organism. During this process, certain cells become committed to specialized functions – a process called differentiation.

    3. Reproduction – Living organisms can reproduce, either sexually or asexually. The offspring produced may resemble the parents in appearance (such as human babies) or be identical to the parent, both genetically and in appearance (microbes that reproduce by binary fission). This trait is essential since life arises only from preexisting life.

    4. Movement – Living organisms are capable of movement, which can be either external movement (such as walking, flying, or crawling) or internal movement (such as the circulation of blood, transport of food, or cytoplasmic streaming).

    5. Metabolism – Living organisms maintain themselves through metabolic activities. Metabolism is the sum of all chemical processes that occur within an organism. Without the ability to extract nutrients and energy from its environment, an organism would not be able to perform the chemical processes required to keep it from deteriorating.

    These characteristics are used by scientists as a guideline only - not all forms of life possess every one of these characteristics. For example, (1) the rule is that mules (which result from the mating of a horse and a donkey) cannot reproduce and (2) rapidly-dividing embryonic cells do not undergo growth between cell divisions – yet mules and embryonic cells are surely living.

    In addition, some objects have many of these basic characteristics, yet are not living. For instance, a fire, which is not living, can grow, move, reproduce (an ember can be blown to a nearby patch of dry grass), and yes, even metabolize.

    “We said earlier that it is possible for an object to have metabolism, but not be alive. The object we had in mind was fire. Atoms are continuously entering fires, in the fuel or oxygen supply, are involved in a series of chemical changes, and are leaving fires, mainly in carbon dioxide or
    water molecules.” (John Maynard Smith & Eors Szathmary, The Origins of Life: From the Birth of Life to the Origin of Language, Oxford University Press, 1999, p5)
    In addition to the 5 attributes listed above, some references include “chemical uniqueness” (the chemical makeup of an organism is distinct from that of the surrounding environment) as a fundamental characteristic of life. Proteins and nucleic acids, for example, are large, complex, informational macromolecules that are produced only in living cells (excluding laboratory synthesis, of course).




    Finally, another property of living things is that they – acting as autonomous units - can “defy” some laws of nature:

    1. Many animals can, of their own accord, hop vertically (“defying” gravity)

    2. Many animals can be traveling in a straight line and, of their own accord, change course (“defying” inertia)

    3. Many organisms grow more complex as they develop (“defying” the second law of thermodynamics).

    Neither rocks, nor water, nor chairs can perform any of these “defiant” acts in and of themselves.

    “The whole point of the genetic code, for example, is to free life from the shackles of nonrandom chemical bonding. … Life works its magic not by bowing to the directionality of chemistry, but by circumventing what is chemically and thermodynamically “natural”. … The secret of life lies, not
    in its chemical basis, but in the logical and informational rules it exploits. Life succeeds precisely because it evades chemical imperatives.” (Paul Davies, The Fifth Miracle: The Search for the Origin and Meaning of Life, Simon & Schuster, NY, 1999, p 255 - 256)

    3) Self-Replication
    Somewhat recently, a new proposal has been put forth that basically discards the well entrenched cell theory as well as all of the above basic characteristics of life - except for reproduction. That is, if “it” can reproduce by itself (truly self-replicate), then “it” is living. This definition, used mostly by origin-of-life researchers, allows for the classification of a mere single molecule as living (as long as it is both self-sustaining and can self-replicate).


    4) Ability to Evolve
    The final method used to categorize something as living concerns the entity’s ability to evolve. Actually, since a single entity cannot evolve, this criterion applies only to a group or population of entities. Using this method, if a group of entities exists in which the individuals posses genetic material, and mutations can occur in their genetic material, and the individuals can reproduce, then a group of those entities has the potential to adapt to the environment and to changes in the environment over time (because the fitness of the offspring can differ from that of the parents) and the population of entities can evolve.

    “An alternative is to define as living any population of entities possessing those properties needed if the population is to evolve by natural selection. That is, entities are alive if they have the properties of multiplication, variation, and heredity…” (The Origins of Life: From the Birth of Life to the Origin of Language, John Maynard Smith & Eors Szathmary, Oxford University Press, NY, 1999, p 3)


    Viruses
    Viruses are non-cellular, infectious agents that are unable to reproduce by themselves, and must, therefore, highjack the synthetic machinery of a host cell in order to produce more copies of themselves– they are non-cellular obligatory intracellular parasites. Viruses consist of a nucleic acid core (either DNA or RNA, but never both [okay, one update - a year or two ago the Mimi (?) virus was found to have both DNA and RNA]) surrounded by a protein coat called a capsid. Some viruses, called enveloped viruses, also have a lipid membrane covering part or all of their capsid.

    Two methods of “reproduction” exist for viruses: the lytic cycle and the lysogenic cycle. In the lytic cycle, the viral genes immediately overtake a host cell’s translational machinery and release of the hundreds or thousands of newly produced viruses involves the death of that single infected host cell. For these viruses, their genome – which the host cell processes – contains genes for lysozyme, an enzyme that breaks down bacterial cell walls. This gene is expressed late (after most copies of the virus have already been produced) and leads to the lysing (“splitting”) of the host cell, releasing the viral particles. On the other hand, in the lysogenic cycle the viral genes remain dormant for some time and death of the originally infected host cell does not occur. For these viruses, their genes become incorporated into the host cell’s DNA and are processed normally: they get duplicated along with the host cell’s DNA and during cell division even get passed on to progeny cells along with the host cell’s DNA. During the lysogenic cycle, viral genes spread throughout a population of host cells without causing (immediate) death to their hosts. Later, some stimulus may activate the viral genes of one or more descendant cells and lead to the lytic cycle in them (overtaking of those host cells’ translational machinery to produce hundreds or thousands of copies of viruses in each, followed by the lysing of those host cells to free the newly assembled viral particles). Regardless of the method of “reproduction”, any released viral particles are free to infect other cells with which they come into contact. For the most part, a virus outside of a cell, called a virion, is completely inactive and displays no signs of being alive (it is non-cellular and does not reproduce, metabolize, move, grow, or respond to stimuli).

    Viruses straddle the line between the living world and nonliving world, and their classification into one or the other has caused division among scientists for years. Some sources state that viruses are indeed living, others state that they are not (but rather just highly-complex organizations of organic molecules), while yet others are noncommittal (referring to viruses as “quasi-living”).

    According to the cell theory, viruses are not living since they are not composed of one of more cells. Those that favor the self-replication definition of life also should view viruses as inanimate since they cannot reproduce by themselves – they absolutely require the assistance of host cells. Concerning the basic characteristics of life, viruses posses hardly any – they don’t grow, develop, move, or metabolize.

    However, those characteristics that viruses do possess seem to be relatively key ones. Viruses contain at least two of the four organic compounds found in all life forms (proteins and either DNA or RNA), can reproduce (although not unaided), and they can in a sense respond to their environment because they can dock to an appropriate host cell and inject their genetic material (some viruses infect cells in other manners) and their DNA or RNA is subject to genetic mutations. Thus, with reproduction (of sorts) and genetic mutation, they can evolve (but not unaided).

    It appears that as of late, the consensus may be leaning towards the inclusion of viruses into the family of the living, but the issue if far from settled. For example, viruses are not now, nor have they ever been, assigned to any of the three domains of life, nor to any of the five (or six) kingdoms, nor to any phylum, nor to any class. In addition, most have not been assigned to any order (though some bacteriophages – viruses that attack bacteria - have). Virologists have been classifying - or have begun classifying - viruses into species and genera and families, so it appears that eventually viruses will be assigned to an existing higher taxa (or a new one will be created specifically for them).

  7. #7
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    Is it true that viruses in and of themselves are incapable of reproduction if there is not a more advanced form of "life" upon which to act as a sort of parasite?

    My foggy notion of viruses is that they were the first form of molecules containing something like carbon which likes to latch onto other molecules and nitrogen, hydrogen and oxygen possibly, and a touch of sulphur. These molecules were formed accidentally through the forces of heat, moving various elements around so that they had an opportunity to bond with other elements through the forces of wind, water flow, volcanic activity, other kinetic sources and even your basic bubbling chemical activity. They were large inert until:

    One magical day when a seemly combination of a couple of disparate viruses (maybe more than a couple considering the complexity of DNA and stuff like that) luckily and happily united and suddenly acquired the ability to suck in nutrients, reproduce and do the other stuff that are supposed to be the activities of life, the very first, primitive forms of life.

    Viruses came first. Then, the basic, ancient, primitive cells which lack a nucleus, then came the more advanced cells with a nucleus, etc., etc., and onward and upward, sort of, and more complex and possibly more advanced and also forming a nice little opportunity for viruses to grab nutrients and reproduce in their primitive, parasitic way.
    Brother, you can believe in stones as long as you do not hurl them at me. Wafa Sultan

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  8. #8
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    Red face

    Thnx. So... as far as i can tell viruses are not alive according to the 5 attributes of life but they really dont fall under either they "reproduce" by invading cells and using them.

    Ok so that solved why do they replicate them selves?
    "Love the Lord your God with all your heart and all your mind, and love your neighbor as your self, there are no two greater commandments than thes" - Jesus Christ God of the Universe.

  9. #9
    DamEtel Guest
    Quote Originally Posted by omega
    Thnx. So... as far as i can tell viruses are not alive according to the 5 attributes of life but they really dont fall under either they "reproduce" by invading cells and using them.

    Ok so that solved why do they replicate them selves?
    Science doesn't answer WHY, but HOW. If you really think there is a WHY to viral reproduction, ask a theologian or philosopher.

  10. #10
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    How? as opposed to Why? Must tattoo on hand for instant reference.
    Brother, you can believe in stones as long as you do not hurl them at me. Wafa Sultan

    “War is an American way to teach geography,” British soldier

    War is sweet to those who have not tasted it, but the experienced man trembles exceedingly at heart on its approach. – Pindar

  11. #11
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    There is no black and white answer here.

    Our classification system for "life" works well for most instances, this is one instance where it fails.

    If anything, viruses are a prime example of how organic and inorganic are really the same thing, with varying degrees of complexity.

    You should try and visualize viruses as the link that allows you to mesh previously separate branches of Chemistry together.

    Just like the fundamental forces in our universe appear to join together at extremes, so do organic and inorganic.

    From a broad enough stand point, our classification system is actual based on the amount of Order something has, not the complex and unwieldy rules we use at everyday scales.

  12. #12
    DamEtel Guest
    supergrunt: Our classification system for "life" works well for most instances, this is one instance where it fails.

    If anything, viruses are a prime example of how organic and inorganic are really the same thing, with varying degrees of complexity.

    You should try and visualize viruses as the link that allows you to mesh previously separate branches of Chemistry together.

    Just like the fundamental forces in our universe appear to join together at extremes, so do organic and inorganic.
    What? Are you claiming that viruses are inorganic???

  13. #13
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    Quote Originally Posted by simone
    Viruses came first. Then, the basic, ancient, primitive cells which lack a nucleus, then came the more advanced cells with a nucleus, etc., etc., and onward and upward, sort of, and more complex and possibly more advanced and also forming a nice little opportunity for viruses to grab nutrients and reproduce in their primitive, parasitic way.
    How would a virus propogate if it was the "first"?

    Answer: it wouldn't.

    The reason why a virus is so small is because it doesn't contain the genetic material capable of doing the things it requires to survive outside the context of parasitism. Something similar; say, perhaps strands of RNA encased in a liposome, could perform the basics of reproduction and possibly explain the origins. They are not a virus though.

  14. #14
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    Blast! Why the devil not?

    What are those archaic forms of bacteria like? How much do they differ from viruses?

    I like the idea of a happy accident of lipids and whatevers combining one happy day and deciding to replicate.

    And, what kind of DNA and RNA do those archaic forms of bacteria have? How much more complex are these strands of life than a virus?

    And, are viruses the dandruff of cells?
    Brother, you can believe in stones as long as you do not hurl them at me. Wafa Sultan

    “War is an American way to teach geography,” British soldier

    War is sweet to those who have not tasted it, but the experienced man trembles exceedingly at heart on its approach. – Pindar

  15. #15
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    Quote Originally Posted by DamEtel
    What? Are you claiming that viruses are inorganic???
    In a general way yes. But you would have to live with the false generalization you create.

    I am saying that Viruses do not fit into our classification scheme for life or non-life. They sit there on the border exposing the failure of the system.

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