Early in the 20th century, prior to the definitive identification of DNA as the genetic material, proteins were considered a strong candidate for this role. This perspective stemmed from their known structural complexity and diversity. The sheer number of different amino acids (20), coupled with the potential for these amino acids to be arranged in virtually limitless sequences, suggested a capacity to encode a vast amount of information. This was in contrast to the relatively simple structure of DNA, which was then understood to be composed of only four nucleotide bases.
The apparent complexity of proteins offered a compelling explanation for the diversity of traits observed in living organisms. Scientists believed that the subtle variations in protein structure could account for the fine-grained differences between individuals and species. Furthermore, proteins were known to play a central role in enzymatic activity, metabolic pathways, and cellular structure, reinforcing the idea that they were the master molecules controlling life processes. This central role led to the assumption that proteins also held the blueprints for constructing and maintaining the organism.
