# How to determine whether the energy of a stem-loop fold is significant or not?

If I have a predicted RNA stem-loop of energy -0.30 kcal/mol, and another of -4.9 kcal/mol, how do I tell whether such a structure is a significantly stable structure or not? Our two competing hypotheses are that there is some structure with sufficient energetic stability to fold inside a cell, versus the one that there is not.

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A predicted stem loop of what? A nucleotide chain presumably, and most likely RNA but you need to tell us. – terdon Apr 23 '14 at 0:34
Yes, it is an RNA. Allow me to update the original question. Many apologies for being unclear. – ericmjl Apr 23 '14 at 0:46
probably the best way is to make it and see if the sequence forms a stem loop. there are lots of energy calculations based on 3d models and sequences if you'd like to know, but i'm not clear on what is best myself. – shigeta Apr 23 '14 at 2:41
I don't know what you mean by significant. More negative the value of folding energy more is the stability. For better predictions you can use the salt correction formulae. – WYSIWYG Apr 23 '14 at 3:21
are you working on miRNA or tRNA or just other rnas? – user1357 Apr 23 '14 at 6:37

You can convert the $\Delta G$ values into equilibrium constants $K$ using the formula

$$\Delta G = R T \ln K$$