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I'm reading some papers about prokaryotic transcription mechanisms, and I've come across a term I haven't heard before: DNA melting or promoter melting. After reading a bit, it's pretty clear that they're referring to the separation of DNA from the double stranded form to single strands.

Maybe it's just because chemistry isn't my thing, but when I think of melting I think of a solid gaining enough energy to become a liquid. How did the term melting come to apply to DNA in this way? Does the term melting have a more general definition in terms of thermal chemistry?

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What if you just consider melting where the intermolecular forces (here, base pairing) give way? –  Nick T Jan 17 '12 at 15:54
    
There is also the term annealing, which refers to the reverse process. Makes for a pretty good analogy with how metals are processed... –  user132 Jan 17 '12 at 15:56
    
Nick T But intermolecular forces "giving way" is not melting. Melting (in physics) refers to the phase change undergone by a substance from solid to liquid. –  Poshpaws Jan 17 '12 at 17:40
    
From a statistical thermodynamics standpoint, DNA denaturation and renaturation is certainly a phase transition. The question is going from which phase to which? I would argue that the description of a rigid polymer going to a freed fluid polymer sounds like a solid to liquid transition to me. –  bobthejoe Feb 17 '12 at 7:30

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The melting temperature (Tm) of a double stranded DNA tract is defined as the temperature at which 50% of the DNA molecules are dissociated into single strands (and 50% form duplexes). Sure, it has a different meaning than in physics... but it is a really common term in molecular biology and I doubt people will stop to use it anytime soon!

There is a vast amount of literature about the calculation of Tm, which is very important also for practical applications, such as designing PCR primers. This page has some explanations and references about the maths behind it.

I am not sure when the term first appeared, but it has clearly be used since the dawn of molecular biology.

DNA denaturation/renaturation dynamics were first studied in the '60s.

See for instance:

STRAND SEPARATION AND SPECIFIC RECOMBINATION IN DEOXYRIBONUCLEIC ACIDS: BIOLOGICAL STUDIES - J. Marmur and D. Lane - PNAS, 1960

Although Marmur and Lane do not talk about melting temperature, we can find the term already two years later in this 1962 paper:

Effect of Concentration on the Formation of Molecular Hybrids from T4 DNA - Andrzej W. Kozinski and Michael Beer - Biophys J., 1962

Evidently the term was already common there, as they don't care to define it (it's even in the abstract).

Who first used it? I'm not sure, if anyone knows feel free to add a comment or edit the answer.

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Don't get me wrong. I'm not critical of the terminology, nor do I think it's inconsistent. I'm simply interested in the origins of the terminology, and whether it's at all related to other uses of the term, such as in thermodynamics. –  Daniel Standage Jan 18 '12 at 0:28
    
The original researchers working on DNA knew nothing about its structure, but I assume they noticed when you got it above a certain temperature it got much runnier, and named the process accordingly? –  Jeremy Kemball Jul 31 '13 at 18:49

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