I've been to a couple of exobiology conventions. And trust me, defining exactly WHAT life is, and when something is a live is not easy.
A conventional definition
Although there is no universal agreement or agreements on the definition of life, the generally accepted biological manifestations are that life exhibits the following phenomena:
1. Organization - Living things are comprised of one or more cells, which are the basic units of life.
2. Metabolism - Metabolism produces energy by converting nonliving material into cellular components (synthesis) and decomposing organic matter (catalysis). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.
3. Growth - Growth results from a higher rate of synthesis than catalysis. A growing organism increases in size in all of its parts, rather than simply accumulating matter.
4. Adaptation - Adaptation is the accommodation of a living organism to its environment. It is fundamental to the process of evolution and is determined by the individual's heredity.
5. Response to stimuli - A response can take many forms, from the contraction of a unicellular organism when touched to complex reactions involving all the senses of higher animals. Plants also respond to stimuli, but usually in ways very different from animals. A response is often expressed by motion: the leaves of a plant turning toward the sun or an animal chasing its prey.
6. Reproduction - The division of one cell to form two new cells is reproduction. Usually the term is applied to the production of a new individual (either asexually, from a single parent organism, or sexually, from two differing parent organisms), although strictly speaking it also describes the production of new cells in the process of growth.
Originally posted by Darth Jello
NO, this isn't another abortion thread, this is a biology thread.Currently we divide everyting we consider to be alive into three Domains-
Archea-Ancient bacteria
Prokaryota-Bacteria/animals with no nucleus
Eukaryota-Everything elseThe problem is that this leaves viruses and prions out and no one is sure if they are alive by our definition or if they fit anywhere in this model.
Viruses containt DNA but they do not respire, feed, produce waste, or display any signs of life outside of a living medium
Prion's are just rogue, self replicating protiens.So what do you think, are they alive?
Yes, they are alive. But as DiamondBullet said they need a host to do so
Life: that which deliberately makes more of itself.
I submit that the word "deliberately" serves the same function as the word "reasonable" as in "proof beyond a reasonable doubt." Both address gray areas in definitions we are trying to render black and white. We don't understand Life well enough yet to know if we can define it w/o referring to nonempirical elements, ie, a soul.
Originally posted by The Omega
I've been to a couple of exobiology conventions. And trust me, defining exactly WHAT life is, and when something is a live is not easy.A conventional definition
Although there is no universal agreement or agreements on the definition of life, the generally accepted biological manifestations are that life exhibits the following phenomena:
1. Organization - Living things are comprised of one or more cells, which are the basic units of life.
2. Metabolism - Metabolism produces energy by converting nonliving material into cellular components (synthesis) and decomposing organic matter (catalysis). Living things require energy to maintain internal organization (homeostasis) and to produce the other phenomena associated with life.
3. Growth - Growth results from a higher rate of synthesis than catalysis. A growing organism increases in size in all of its parts, rather than simply accumulating matter.
4. Adaptation - Adaptation is the accommodation of a living organism to its environment. It is fundamental to the process of evolution and is determined by the individual's heredity.
5. Response to stimuli - A response can take many forms, from the contraction of a unicellular organism when touched to complex reactions involving all the senses of higher animals. Plants also respond to stimuli, but usually in ways very different from animals. A response is often expressed by motion: the leaves of a plant turning toward the sun or an animal chasing its prey.
6. Reproduction - The division of one cell to form two new cells is reproduction. Usually the term is applied to the production of a new individual (either asexually, from a single parent organism, or sexually, from two differing parent organisms), although strictly speaking it also describes the production of new cells in the process of growth.
These are the criteria that are often looked to when deciding whether something is alive or not. Neither prions nor viruses are eligible for being considered alive.
A virus, in all actuality, is simply a few strands of DNA or RNA, a protective protein coat, and possibly a few enzymes so that its genetic material can be translated.
A virus is not organized; it is not even a single cell, and lacks mitochondria, cytoplasm, and other basic cellular units.
A virus does not have a metabolism; it can never perform any chemical reactions without the help of a host cell. This is why antibiotics do not work on viruses; antibiotics target and disrupt the metabolism, and with nothing to disrupt they do not work.
A virus never actually grows; it is put together using the instructions of another virus' DNA or RNA inside of a host cell.
A virus never adapts to its surroundings. It can force a host cell to adapt to surroundings by rupturing and the like, but the virus itself can not adapt in such a fashion. This statement also addresses response to stimuli.
A virus does not reproduce. It creates copies of itself through a host cell, and never actually goes through mitosis because, well, it's not a cell.
I will readily admit that I do not know much about Prions, so feel free to correct me on anything in the below section.
A prion, as I understand it, is simply a protein folded into a beta sheet, or perhaps a more complex form such as a tertiary or quaternary structure. Thus, it is not a cell and therefore lacks the required organization.
A prion is a protein. It doesn't carry out any chemical reactions; thus, it does not have a metabolism.
A prion cannot grow. Something that lacks any genetic material whatsoever simply cannot.
A prion is an abnormal form of a "prion protein" located in the brain. How is it possible for a protein to adapt to its environment?
Again, this does not even seem possible. It is a protein. I can't see how it could logically respond to stimuli in its environment. Folding from a beta sheet to a tertiary structure perhaps, but that isn't something that I would consider response to stimuli.
Prions are not known to reproduce themselves; they are created by cells not by each other.
Any questions?
Originally posted by Darth Jello
NO, this isn't another abortion thread, this is a biology thread.Currently we divide everyting we consider to be alive into three Domains-
Archea-Ancient bacteria
Prokaryota-Bacteria/animals with no nucleus
Eukaryota-Everything elseThe problem is that this leaves viruses and prions out and no one is sure if they are alive by our definition or if they fit anywhere in this model.
Viruses containt DNA but they do not respire, feed, produce waste, or display any signs of life outside of a living medium
Prion's are just rogue, self replicating protiens.So what do you think, are they alive?
prions are just some protein parts.. so a big no
and viruses... they're not able to carry out (?) methabolism outside the host cells... so it should be counted not as life, as well...