visual guide

Here is my simple method.

The correct GC order.

The incorrect GC order.

How to know? Notice each N has two arms. Think of them as grabbers. In pic 1 the power G has to only slightly change the position of one arm to grab the C. In pic 2 the power G has to swing its upper arm around over 90 degrees from natural position to grab C. With this extra effort, less power is available to reduce the positive value of the loop.

Correct GC order , correct UA relationship.

Correct GC order , incorrect UA relationship.

How to know? GA must attract a nominal but inconsequential amount - otherwise the RNA would fall apart. We know GU attracts , so with the U across from the G the loop closing is reinforced a small amount. With the U adjacent to the G only the strength of the string is reinforced.

The next two pics show that with an incorrect GC order , UA position has no bearing.


In conclusion and in general , do not force any N to “put its arm(s) behind its back” to make a connection unless there is no other choice.
Of course, this probably flies in the face of jargon, but it works for me.