Most extant organisms synthesize proteins using the 20 kinds of amino acids that are coded by the standard genetic code table. Currently, these amino acids are incorporated from the environment or synthesized via biosynthetic pathways. However, primordial proteins should have been synthesized only from prebiotically available amino acids. It is not clear, at the moment, whether all 20 coded amino acids were present in sufficient concentrations in the prebiotic environment. Therefore, it could be possible that primordial proteins were synthesized from significantly fewer than 20 kinds of amino acid. Herein, I review previous attempts to synthesize proteins from a limited set of the 20 amino acids and discuss about the possibility of simpler constituents for primordial proteins.
Extraterrestrial organic matter provided by meteorites and interplanetary dust particles could have been contributed to the origin of life on the Earth. As a part of chemical evolution toward life, it is important to understand origin and evolution of organic matter in the Solar System and beyond. Formation and evolution of organic matter in the Solar System have been studied over decades. Although organic matter usually exists with minerals as in meteorites, effects of minerals for the processes of extraterrestrial organic matter are not well understood. Here I review the relationships between organic matter and minerals observed in meteorites, experimental studies of interactions of organic matter with minerals, and mechanisms of effects of minerals for organic reactions.