Comment by cyberax
1 hour ago
Life can even use something other than amino acids. They are really inconvenient when you think about it. Fixed nitrogen is extremely rare, and there are no nitrogen-containing minerals other than some exotic exceptions.
Amino acids are useful because they can be easily joined together and split apart (via the C-N bond). But there are other types of "molecular glues" that are viable, like sulfur or phosphorus.
Amino acids are much more likely to be involved in the appearance of life anywhere than other molecules.
For instance it would be much less surprising if an alien life form used another kind of polymer to store information, instead of nucleic acids, than if it would not use amino acids. The fact that on Earth the living beings eventually used ATP and RNA appears to have been determined in great part by chance, while the use of amino acids seems to have been much more deterministic.
Some of the simple amino acids are very easy to be synthesized in abiotic conditions, which is why they are ubiquitous in many celestial bodies.
The advantage of amino acids is that they do not contain only one end that can be attached to other molecules, but that they contain two such ends. A molecule with only one connector would attach to another, forming a dimer, after which no further reaction is possible.
A molecule with two connectors, like an amino acid that has both a carboxyl end and an amine end, can be daisy chained into a polymer of arbitrary length. This allows building complex structures.
There are other molecules with two connectors, but they are much more unlikely to appear in abiotic conditions.
Thioesters, i.e. a kind of organic molecules that are bound by a sulfur bridge, like you mention, appear to have been much more important when life has appeared on Earth than today, but such molecules were important as intermediates in metabolic reactions, not as structural blocks, like amino acids, and there are no known naturally-produced molecules with sulfur that could be used as easily as amino acids to make molecules with arbitrary complex shapes.