Kostenloser DNA Melting Temperature Rechner
Berechnen Sie DNA melting temperature (Tm) aus oligonucleotide length und GC content unter Verwendung von Wallace und Marmur-Doty formulas.
Tm (Wallace Rule, short oligos)
60.0 °C
Tm (Wallace Rule, short oligos) vs Oligonucleotide Length
Formel
## DNA Melting Temperature The melting temperature (Tm) is the temperature at which 50% of double-stranded DNA molecules are denatured into single strands. ### Wallace Rule (for short oligos < 20 bp) **Tm = 2(A+T) + 4(G+C)** °C ### Marmur-Doty (for longer DNA) **Tm = 64.9 + 41 × (G+C - 16.4) / N** °C GC base pairs have three hydrogen bonds (vs two for AT), making them more thermally stable.
Lösungsbeispiel
A 20-mer with 10 GC bases and 10 AT bases.
- 01AT count = 20 - 10 = 10
- 02Wallace: Tm = 2(10) + 4(10) = 20 + 40 = 60°C
- 03GC content = 10/20 × 100 = 50%
Häufig Gestellte Fragen
When should I use each formula?
The Wallace rule is best for short oligonucleotides (< 20 bp) like PCR primers. The Marmur-Doty and nearest-neighbor thermodynamic methods are better for longer sequences. Salt concentration and mismatches also affect Tm.
How does salt affect Tm?
Higher salt concentration stabilizes DNA by neutralizing backbone charges, increasing Tm. A common correction: Tm increases by about 16.6°C per log10 increase in [Na+].
Why is Tm important for PCR?
PCR annealing temperature is typically set 3-5°C below the Tm of the primers. If the annealing temperature is too high, primers do not bind; too low, and nonspecific binding occurs.
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