Natural selection of specific protobiomonomers during abiogenic development of the prototype genetic code is hindered by the diversity of structural, spatial, and rotational isomers that have identical elemental composition and molecular mass (M), but can vary significantly in their physicochemical characteristics, such as the melting temperature T_m, the T_m:M ratio, and the solubility in water, due to different positions of atoms in the molecule. These parameters differ between cis- and trans-isomers of dicarboxylic acids, spatial monosaccharide isomers, and structural isomers of α-, β-, and γ-amino acids. The stable planar heterocyclic molecules of the major nucleobases comprise four (C, H, N, O) or three (C, H, N) elements and contain a single –C=C bond and two nitrogen atoms in each heterocycle involved in C–N and C=N bonds. They exist as isomeric resonance hybrids of single and double bonds and as a mixture of tautomer forms due to the presence of –C=O and/or –NH₂ side groups. They are thermostable, insoluble in water, and exhibit solid-state stability, which is of central importance for DNA molecules as carriers of genetic information. In M–T_m diagrams, proteinogenic amino acids and the corresponding codons are distributed fairly regularly relative to the distinct clusters of purine and pyrimidine bases, reflecting the correspondence between codons and amino acids that was established in different periods of genetic code development. The body of data on the evolution of the genetic code system indicates that the elemental composition and molecular structure of protobiomonomers, and their M, T_m, photostability, and aqueous solubility determined their selection in the emergence of the standard genetic code.

在原型遗传密码的非生物发育过程中，特定原生物单体的自然选择受到结构、空间和旋转异构体的多样性的阻碍，这些异构体具有相同的元素组成和分子质量 (M)，但它们的物理化学特征可能会有显着差异，例如由于分子中原子的位置不同，熔化温度 T _m、T _m :M 比率以及在水中的溶解度。这些参数在顺式和反式之间有所不同-二羧酸的异构体、空间单糖异构体以及α-、β-和γ-氨基酸的结构异构体。主要核碱基的稳定平面杂环分子包含四个 (C, H, N, O) 或三个 (C, H, N) 元素，并包含单个 –C=C 键和每个参与 C– 的杂环中的两个氮原子N 和 C=N 键。由于存在–C=O 和/或–NH ₂侧基，它们以单键和双键的异构共振杂化物和互变异构体形式的混合物存在。它们是热稳定的，不溶于水，并表现出固态稳定性，这对于作为遗传信息载体的 DNA 分子至关重要。在 M–T_米从图中可以看出，蛋白质氨基酸和相应的密码子相对于嘌呤和嘧啶碱基的不同簇分布相当规律，反映了在遗传密码发展的不同时期建立的密码子和氨基酸之间的对应关系。遗传密码系统演化的大量数据表明，原始生物单体的元素组成和分子结构，以及它们的 M、T _m、光稳定性和水溶性决定了它们在标准遗传密码出现时的选择。