6 ms·

"As small as life can get" is an interesting claim. Without reading the paper I am wondering if life before bacteria wouldn't have to be smaller. Maybe even dev

"As small as life can get" is an interesting claim. Without reading the paper I am wondering if life before bacteria wouldn't have to be smaller. Maybe even devoid of membranes. At the very beginning there should even have been molecules which catalyzed (=enhanced) their own synthesis, first a little, then progressively more until you had something like an RNA replication machine... And then these bacteria come pretty close to virus and cell organelles, raising questions of when to call a parasite "life" or "not life".

TheSpiceIsLife 12y ago
Prions self replicate, but require the host to have the correctly folded protein.[1] Of course there's viruses too, which are self replicating but need to infect some other organism. Maybe crystals? Now we're getting in to the potentially wonky question of 'what is life?' 1. http://en.wikipedia.org/wiki/Prion http://en.wikipedia.org/wiki/Prion Edit: grammar for clarity.
- fabian2k 12y ago
  Prions are not considered alive under any reasonable definition of life. They're infectious, but you can't really call it replication as they just trigger a conformational change in the correctly folded prion protein
  - TheSpiceIsLife 12y ago
    Yes, that's true. I should not have included the word 'self' with regard to prions. Are viruses considered 'alive'?
    - lepton 12y ago
      No. Viruses require a live host in order to replicate. That sounds tautological, but I'm not sure how else to say it briefly.
      - xkcd-sucks 12y ago
        It's begging the question... every 'living' organism also requires a favorable environment in order to replicate
bazzargh 12y ago
What they actually said was "This is the smallest a cell can be and still accommodate enough material to sustain life" - this was shortened in the lede. But "as small as life can get" is a thing that has been studied, eg for Mars Sample-Return missions, they have to figure out a safe filter size (chapter 3): http://science.nasa.gov/media/medialibrary/2013/01/17/ESF_Mars_Sample_Return_backward_contamination_study.pdf http://science.nasa.gov/media/medialibrary/2013/01/17/ESF_Ma... An important distinction is whether these organisms can live 'independently' - a virus relies on a host. Quoting from the doc above: it is believed that theoretically a coccoid[1] cell with the minimum number of genes to be free living in an environment other than a living host would have a minimum cell diameter of approximately 0.15–0,2 μm. - which is around about the size of the beasties in the parent article. They did consider smaller biological entities though, like gene transfer agents[2], and recommended filters such that nothing over 0.05μm is released under any circumstances, and that there's only a 1 in a million chance of anything smaller than 0.01μm escaping. [1] Spherical. http://en.wikipedia.org/wiki/Coccoid http://en.wikipedia.org/wiki/Coccoid [2] http://en.wikipedia.org/wiki/Gene_transfer_agent http://en.wikipedia.org/wiki/Gene_transfer_agent

TheSpiceIsLife 12y ago

Prions self replicate, but require the host to have the correctly folded protein.[1] Of course there's viruses too, which are self replicating but need to infect some other organism. Maybe crystals? Now we're getting in to the potentially wonky question of 'what is life?' 1. http://en.wikipedia.org/wiki/Prion http://en.wikipedia.org/wiki/Prion Edit: grammar for clarity.

fabian2k 12y ago
Prions are not considered alive under any reasonable definition of life. They're infectious, but you can't really call it replication as they just trigger a conformational change in the correctly folded prion protein
- TheSpiceIsLife 12y ago
  Yes, that's true. I should not have included the word 'self' with regard to prions. Are viruses considered 'alive'?
  - lepton 12y ago
    No. Viruses require a live host in order to replicate. That sounds tautological, but I'm not sure how else to say it briefly.
    - xkcd-sucks 12y ago
      It's begging the question... every 'living' organism also requires a favorable environment in order to replicate

bazzargh 12y ago

What they actually said was "This is the smallest a cell can be and still accommodate enough material to sustain life" - this was shortened in the lede. But "as small as life can get" is a thing that has been studied, eg for Mars Sample-Return missions, they have to figure out a safe filter size (chapter 3): http://science.nasa.gov/media/medialibrary/2013/01/17/ESF_Mars_Sample_Return_backward_contamination_study.pdf http://science.nasa.gov/media/medialibrary/2013/01/17/ESF_Ma... An important distinction is whether these organisms can live 'independently' - a virus relies on a host. Quoting from the doc above: it is believed that theoretically a coccoid[1] cell with the minimum number of genes to be free living in an environment other than a living host would have a minimum cell diameter of approximately 0.15–0,2 μm. - which is around about the size of the beasties in the parent article. They did consider smaller biological entities though, like gene transfer agents[2], and recommended filters such that nothing over 0.05μm is released under any circumstances, and that there's only a 1 in a million chance of anything smaller than 0.01μm escaping. [1] Spherical. http://en.wikipedia.org/wiki/Coccoid http://en.wikipedia.org/wiki/Coccoid [2] http://en.wikipedia.org/wiki/Gene_transfer_agent http://en.wikipedia.org/wiki/Gene_transfer_agent