nucleotides. Internal-loops differ from Stem-loops
as they occur in middle of a stretch of double stranded RNA. The non-canonicoal residues result in the double helix becoming distorted due to unwinding, unstacking and kinking.
Internal-loops can be classified as either symmetrical or asymmetrical, with some asymmetrical internal-loops, also known as bulges. Many important structural motifs are composed of internal loops such as
the C-loop,[1]
the docking-elbow,[2]
kink-turns (k-turn),[3][4]
the right-angle,[5]
the sarcin/ricin loops (also called bulged-G motifs),[6][7][8]
the twist-up motif[9]
and the UAA/GAN internal loop motif.[10]
![A consensus secondary structure and primary sequence for the 3` Sarcin-Ricin (or bulged-G) RNA motif.[6]](/File:Sarcin-ricin-1-secondary-structure.svg)
![A consensus secondary structure and primary sequence for the 5` Sarcin-Ricin (or bulged-G) RNA motif.[6]](/File:Sarcin-ricin-2-secondary-structure.svg)
![A consensus secondary structure and primary sequence for the twist-up RNA motif.[9]](/File:Twist_up-secondary-structure.svg)
![A consensus secondary structure and primary sequence for the UAA-GAN RNA motif.[10]](/File:UAA_GAN-secondary-structure.svg)