DNA to mRNA Converter

Which strand you were handed decides everything — get it wrong and every base is wrong.

mRNAAUGGCCUACGGAUUCthe coding strand with U replacing T

Complementary strandTACCGGATGCCTAAGbase by base, written against the input

Reverse complementGAATCCGTAGGCCATthe other strand read in its own 5' to 3' direction

Length15 bases5 codons

GC content53.333%

Melting temperature41.94 °CMarmur rule, for a 15-base oligo

Molar mass as double-stranded DNA9.75 × 10³ g/mol

Because this is the coding strand, the mRNA reads the same but for U in place of T. The template strand is the reverse complement shown above.

The formula

coding strand: T becomes U ; template strand: reverse complement, then T becomes U

Which strand were you given?

This is the whole difficulty. The mRNA matches the CODING strand, base for base, with uracil replacing thymine. It is built against the TEMPLATE strand, so from that one you must take the reverse complement first. Feed a template strand into the coding-strand rule and every base of the answer is wrong — not slightly wrong, wrong throughout.

Uracil instead of thymine

RNA uses uracil where DNA uses thymine, and thymine is simply uracil with a methyl group added. The usual explanation is that cytosine spontaneously deaminates into uracil, so a DNA repair system that treats uracil as damage can find and fix those events. That only works if uracil does not belong in DNA in the first place — the methyl group is what makes the error detectable.

GC content and melting

Guanine-cytosine pairs are held by three hydrogen bonds against adenine-thymine's two, so GC-rich sequences melt at higher temperatures. That is why melting temperature estimates depend on GC content and why primer design cares about it.

Ratios are expectations, not promises

Every genetic ratio on these pages is a probability distribution, not a guarantee. A 3:1 cross does not produce three dominant offspring for every recessive one in a litter of four — it produces each offspring independently with a three-quarters chance. Small families depart from the expected ratio routinely, and that is the reason Mendel needed thousands of pea plants rather than dozens.