The question is what exactly is the structure of these RNA molecules? Well, unlike DNA molecules which exist in a double stranded form, RNA molecules inside our cells exist mostly as single strands of nucleotides. But these single trans of nucleotides under the conditions found in our cells usually twist and fold into a well defined threedimensional structure. Now, the most common type of form that these RNA molecules fold into is known as a stem loop form. And this stem loop form is formed when the ribonucleic acid folds into this double helical structure just like in DNA in which we contain these complementary sequences, these complementary nucleotides that can form base pairs. But in these stem loop structures we also commonly contain these mismatched nucleotides and that destabilizes our structure in that localized region and causes the bulging out of that structure as we'll see in just a moment.