A Formal Definition of Single-Stranded DNA Molecular Weight

DNA is commonly treated as a symbolic sequence. Its basic physical properties are rarely made explicit at a theoretical level. In this work, we formally define the molecular weight of a single-stranded DNA (ssDNA) sequence as a primary quantity derived from the sum of the masses of the nucleotide residues incorporated into the chain. We show that this definition is deterministic, additive, and independent of base order. In addition, we define mass skew as the weight difference between a sequence and its complementary strand. This work assigns no functional meaning to the quantities introduced and is limited to the formalization of intrinsic physical measures of the FASTA sequence.