Читать книгу Astrobiology - Charles S. Cockell - Страница 77

When we search for life on other planets, it seems that we have no choice but to base this search on the life that we know on Earth. However, is that the case? Is there a way of searching for life while making the minimum number of assumptions about its biochemistry? You might like to discuss with your fellow students what features of life could be universal, but that make no assumptions about the particular chemical make-up of life. For example, life tends to form chains of monomers that then assemble into larger structures. In our own form of life, proteins, carbohydrates, membrane lipids, and nucleic acids are examples. In general, non-biological processes do not form chains as long as proteins (several hundred to over a thousand amino acids). One way to search for life could be to build a machine that looks for long chains of molecules. Chirality is another characteristic of biology. The use of almost exclusively L-amino acids in terrestrial life may be a result of it selecting only one form so that biochemistry does not suffer the inefficiency of having to use, and thus build enzyme and other metabolic systems to deal with, two enantiomers of the same amino acid. Would all life have a chiral preference for L or D forms of amino acids and sugars? Could we search for life by searching for an excess of one particular enantiomer? Consider other facets of life that could be universal and could provide a way to detect it while minimizing assumptions about its particular biochemical make-up.

Johnson, S.S., Anslyn, E.V., Graham, H.V. et al. (2018). Fingerprinting non-terran biosignatures. Astrobiology 18: 915–922.

MacDermott, A.J, Barron, L.D., Brack, A. et al. (1996). Homochirality as the signature of extra-terrestrial life. Origins and of Life and Evolution of Biospheres 26: 246–247.