680,000
Da
680
kDa
680,000
Da
680
kDa
The RNA Molecular Weight Calculator estimates the molecular weight of a single-stranded RNA molecule based on its length in nucleotides. Using the average molecular weight of 340 Da per ribonucleotide, this tool quickly provides the MW in both Daltons and kiloDaltons. Knowing the molecular weight of your RNA is important for gel electrophoresis analysis, copy number calculations, and in vitro translation experiments.
The molecular weight is calculated using the average ribonucleotide mass:
MW (Da) = Length (nt) × 340 Da/nt
Where 340 Da is the average molecular weight of a single ribonucleotide (considering the four bases AMP, UMP, GMP, CMP in roughly equal proportions, minus water lost during polymerization).
For reference, individual ribonucleotide monophosphate weights are:
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A 2000-nucleotide mRNA has a molecular weight of approximately 680,000 Da (680 kDa).
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A typical 22-nucleotide microRNA has a molecular weight of approximately 7,480 Da (7.48 kDa).
RNA nucleotides contain a ribose sugar with a 2'-hydroxyl group, making each nucleotide slightly heavier than the corresponding deoxyribonucleotide in DNA. Additionally, RNA contains uracil instead of thymine, which has a slightly different mass. The average across all four RNA nucleotides works out to approximately 340 Da per nucleotide.
No, this calculator uses total nucleotide length only. If your mRNA has a 5' 7-methylguanosine cap (adds ~503 Da) and a poly(A) tail (typically 200–250 adenosines), you should include the poly(A) nucleotides in the total length. The cap adds negligible mass relative to the total for most transcripts.
On denaturing agarose or polyacrylamide gels, RNA migration is primarily determined by molecular weight (length). Larger RNA molecules migrate more slowly. However, under non-denaturing conditions, RNA secondary structure can cause aberrant migration. Always use denaturing conditions (formaldehyde agarose or urea-PAGE) for accurate size determination.
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