4 ms·

I agree, but as far as we know life evolved only once, and particular chiral orientations in central carbon metabolism were then locked forever, because they ca

by _yb2s 2y ago

I agree, but as far as we know life evolved only once, and particular chiral orientations in central carbon metabolism were then locked forever, because they can't be changed without breaking everything else. The same enzymes won't generally work with both steroisomers- every enzyme they interact with needs radical structural changes. Less critical things outside of central carbon metabolism often do evolve different stereoisomers in different species, or even the same species. For example, the large macrocyclic antibiotic molecules sometimes evolve to flip sterochemistry, creating a new antibiotic.

soco 2y ago
Why should we talk about "same enzymes"? There's a 50% chance to have "other enzymes" working for the other orientation, whenever we find life similar to ours (which it doesn't have to be). Or is there any reason why other orientation cannot exist?
- snapplebobapple 2y ago
  For any multistep reaction there is a strong likelihood that "other enzymes" would make something that does not work for the next step (depends on the 3d shape not fitting in the next enzyme). So at best some of the intermediary products for each organism with opposite chirality enzymes may not work in the other, at worst, it may be actively poisonous. Since time + competition breeds monopoly one would expect to see only one per competition zone (i.e. planet) given sufficient time. You could see both if there was an active breakdown mechanism developed in each that allowed minimally inefficient usage of the others resources (i.e. we see this on a macro level with things like lobster blood using copper instead of iron and being blue. We can still eat each other no problem without getting sick so there's no pressure to get rid of the one system)
- _yb2s 2y ago
  If you’re talking about hypothetical extraterrestrial life that evolved separately- sure. But as far as we know all life, at least on earth has a common ancestor and is heavily locked into the existing enzymes and substrates- basic central carbon metabolism is virtually identical in all living things.

by _yb2s 2y ago

soco 2y ago

Why should we talk about "same enzymes"? There's a 50% chance to have "other enzymes" working for the other orientation, whenever we find life similar to ours (which it doesn't have to be). Or is there any reason why other orientation cannot exist?

snapplebobapple 2y ago
For any multistep reaction there is a strong likelihood that "other enzymes" would make something that does not work for the next step (depends on the 3d shape not fitting in the next enzyme). So at best some of the intermediary products for each organism with opposite chirality enzymes may not work in the other, at worst, it may be actively poisonous. Since time + competition breeds monopoly one would expect to see only one per competition zone (i.e. planet) given sufficient time. You could see both if there was an active breakdown mechanism developed in each that allowed minimally inefficient usage of the others resources (i.e. we see this on a macro level with things like lobster blood using copper instead of iron and being blue. We can still eat each other no problem without getting sick so there's no pressure to get rid of the one system)
_yb2s 2y ago
If you’re talking about hypothetical extraterrestrial life that evolved separately- sure. But as far as we know all life, at least on earth has a common ancestor and is heavily locked into the existing enzymes and substrates- basic central carbon metabolism is virtually identical in all living things.