RNA is Single-Stranded

RNA is a polymer of nucleotides that's similar to DNA. The biggest difference between RNA and DNA is that RNA is a single stranded molecule while DNA is double stranded (a double helix).

Another difference is that RNA does not use thymine as a nucleotide base, instead, it uses a base called uracil. Uracil can form a base pair with adenine in RNA, just like thymine does in DNA. Here is a summary of the differences between RNA and DNA.

The fact that RNA is single stranded allows it to assume various unique shapes.

There is no second strand to lock it into a double helix shape. It can form base pairs with itself, and this allows it to fold up into many different three-dimensional shapes.