Urea linearizes nucleic acids during electrophoresis

When we want to know the length of RNA, we perform an electrophoresis using a gel. However, RNA generally forms a secondary structure, which makes it difficult to get the result of electrophoresis reflecting the exact length of RNA. The secondary structure of RNA is formed by hydrogen bonds of bases in the nucleic acid. Urea dissociates the hydrogen bonds of nucleic acid. Therefore, we can perform an electrophoresis at the state of linear RNA by adding urea into the gel.