Subject: Why do the mRNA nucleotides in a cell not bond to eachother?

I have been learning about protein synthesis and was wondering what prevents 
the mRNA nucleotides from bonding to eachother in their complementary base 
pairs, as i have read that they are much more stable as pairs than on their 
own. If they do join, but are broken apart again to bond with the antisense 
strand, how does this happen? Is it an enzyme, and if so what type of enzyme 
and how exactly.

Thanks very much for reading this,
Katie

Re: Why do the mRNA nucleotides in a cell not bond to eachother?