It is an interesting question for a biochemical scientist as to why , of all the myriads of molecules present in the biosphere and in the organic world, deoxyribonucleic acid was chosen to convey the message of inhertable traits from one generation to the other.
One of the primary reasons is that DNA is endowed with the property to replicate. Of carbohydrates , lipids , proteins and all other biological , organic derivatives found in the living world none can produce a duplicate of itself. This obviously excludes such biomolecules to function as heritable matter for when a cell splits into two , whatever the carrier of the heritable message must also duplicate into two. DNA fulfills this function.
Not only does DNA replicate itself , it does so without making many mistakes . That is a big plus. If I were to ask you to copy Shakespeare word for word , you would certainly make an error or two , if only in the missplacement of a punctuation mark . But that punctuation mark , as any reader will tell you, can be crucial to the meaning of the sentence. Thus it is important that DNA duplicate itself without much error. And thankfully , there is a whole army of proteinaceous soldiers waiting in the wings to correct any error that may occur during the replication of DNA.
The complexity of the DNA molecule is sufficient to encode the messages needed. That is a crucial criteria for the complexity of the building blocks of DNA reflects the complexity of the message that can be conveyed therein.