Calculateur de Temps de Doublement Cellulaire
Calculez le temps de doublement d'une culture cellulaire.
Tm (Wallace Rule, short oligos)
60.0 °C
Tm (Wallace Rule, short oligos) vs Oligonucleotide Length
Formule
## 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.
Exemple Résolu
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%
Questions Fréquentes
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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