4 ms·

"Life" means splitting hairs finer and finer. Are bacteria alive? Viruses? Prions? The distinction is ultimately meaningless.

olliej 7y ago
Bacteria are alive by all standard definitions of life. Generally viruses and prions are not considered alive as they are not (theoretically) capable of self replication. Viruses don't have any of the mechanisms required for self replication - they only reproduce if a different organism is coerced into duplicating the virus's genetic material. Specifically the virus genetic material gains precedence over the cell's own material once the cell dissolves the protein shell. Prions are literally misfolded proteins - saying they're alive is not different from saying any arbitrary polymer is alive - plenty of polymerization processes essentially have the same construction behaviour: rely on the bond affinities to morph neighboring identical molecules into identical construction.
- dekhn 7y ago
  Prions definitely self-replicate. the criterion for life is metabolism addition to self reproduction
  - ncmncm 7y ago
    No, they don't. When they come in contact with another, already synthesized, protein of identical composition, they alter it to match their own shape. That is a far cry from replication or reproduction. The other protein has an equal role, in its readiness to conform. Other molecules alter the shape of proteins not like themselves, in otherwise similar ways. We don't call them alive, either. Prions are interesting in that their action produces more identical action, in an exponentially growing fashion, unlike other, otherwise similar, processes. If you like, you could say the prion's shape, itself, reproduces, given a substrate of conformable prionic proteins. That makes it more like a meme.
    - dekhn 7y ago
      I got my phd in biophysics from UCSF, where the prion work was originally done, and all my professors used the term "replication". That was a colloquial term for "catalyze a structural transfer in an exponential way". I think that really does qualify for replication in a limited way. However, arguing over this terminology is irrelevant.
      - ncmncm 7y ago
        Agreed. The exponential character makes it eerily similar to life processes. I wonder whether anyone has measured temperature reduction in a runaway prion replication process.
jamesrcole 7y ago
I agree. "Life" isn't some category out there in the world that has absolute boundaries. It's a human concept. In reality there's a gradient of more and more sophisticated kinds of processes, and there's no absolute cut off point between non-living and living. It's the human need to have absolute categories that makes it seem like it is a binary category. Richard Dawkins has written an excellent essay on this matter (the human desire for absolute categories): The tyranny of the discontinuous mind https://www.newstatesman.com/blogs/the-staggers/2011/12/issue-essay-line-dawkins https://www.newstatesman.com/blogs/the-staggers/2011/12/issu... He's also written about this topic here: https://www.edge.org/response-detail/25366 https://www.edge.org/response-detail/25366
fifnir 7y ago
They use the same genetic code as us, what's your definition of life? Having access to Netflix ?

olliej 7y ago

Bacteria are alive by all standard definitions of life. Generally viruses and prions are not considered alive as they are not (theoretically) capable of self replication. Viruses don't have any of the mechanisms required for self replication - they only reproduce if a different organism is coerced into duplicating the virus's genetic material. Specifically the virus genetic material gains precedence over the cell's own material once the cell dissolves the protein shell. Prions are literally misfolded proteins - saying they're alive is not different from saying any arbitrary polymer is alive - plenty of polymerization processes essentially have the same construction behaviour: rely on the bond affinities to morph neighboring identical molecules into identical construction.

dekhn 7y ago
Prions definitely self-replicate. the criterion for life is metabolism addition to self reproduction
- ncmncm 7y ago
  No, they don't. When they come in contact with another, already synthesized, protein of identical composition, they alter it to match their own shape. That is a far cry from replication or reproduction. The other protein has an equal role, in its readiness to conform. Other molecules alter the shape of proteins not like themselves, in otherwise similar ways. We don't call them alive, either. Prions are interesting in that their action produces more identical action, in an exponentially growing fashion, unlike other, otherwise similar, processes. If you like, you could say the prion's shape, itself, reproduces, given a substrate of conformable prionic proteins. That makes it more like a meme.
  - dekhn 7y ago
    I got my phd in biophysics from UCSF, where the prion work was originally done, and all my professors used the term "replication". That was a colloquial term for "catalyze a structural transfer in an exponential way". I think that really does qualify for replication in a limited way. However, arguing over this terminology is irrelevant.
    - ncmncm 7y ago
      Agreed. The exponential character makes it eerily similar to life processes. I wonder whether anyone has measured temperature reduction in a runaway prion replication process.

jamesrcole 7y ago

I agree. "Life" isn't some category out there in the world that has absolute boundaries. It's a human concept. In reality there's a gradient of more and more sophisticated kinds of processes, and there's no absolute cut off point between non-living and living. It's the human need to have absolute categories that makes it seem like it is a binary category. Richard Dawkins has written an excellent essay on this matter (the human desire for absolute categories): The tyranny of the discontinuous mind https://www.newstatesman.com/blogs/the-staggers/2011/12/issue-essay-line-dawkins https://www.newstatesman.com/blogs/the-staggers/2011/12/issu... He's also written about this topic here: https://www.edge.org/response-detail/25366 https://www.edge.org/response-detail/25366

fifnir 7y ago

They use the same genetic code as us, what's your definition of life? Having access to Netflix ?