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Drybench Sequence.
DNA molecular weight calculator
The molecular weight of a DNA or RNA strand from its residue formulas and the IUPAC 2021 atomic weights, with the end convention stated.
Sequence
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Answer
DNA molecular weight
The exact molecular weight from the residue formulas and the IUPAC 2021 atomic weights, with the end convention stated.
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Worked example
- The T7 promoter primer, 20 nt single-stranded with 5′-OH and 3′-OH ends: 6125.05 g/mol, C196H246N77O116P19, as a neutral free acid with the CIAAW 2021 atomic weights.
- A 5′-phosphate adds 79.98 g/mol; double-stranded adds the complementary strand; circular adds nothing, since no end gains water.
Method
Σ residue formulas (nucleoside monophosphate less water) plus the end groups, summed with CIAAW 2021
- Nucleic acid molecular weight from the sequence. Residue formulas from the nucleoside 5′-monophosphates (PubChem, read 6 October 2026) less water, summed with the IUPAC CIAAW 2021 atomic weights; 5′-OH and 3′-OH ends as a neutral free acid.Checked against hand arithmetic from the cited residue masses within 0.01 g/mol on 5 oligos (6 October 2026).
Constants
- ciaaw-2021: IUPAC CIAAW 2021 standard atomic weights, conventional values for interval elements
Limits
- For research and education only, and not medical advice: nothing here is an assessment of any person's variant, sample or molecule, and a difference reported from a reference is a difference, not an interpretation.
- Tags and protease sites are found by their published motifs and a cut is proposed at the site nearest an end; confirm it, since a motif inside the protein is not a cleavage site.