Ribozymes are RNA molecules that can catalyze chemical reactions, including RNA cleavage. They function by stabilizing the transition state and lowering the activation energy required for the cleavage reaction. One of the most well-known ribozymes is the hammerhead ribozyme, which catalyzes the cleavage of RNA at specific sites. The ribozyme's active site typically contains critical nucleotides and metal ions that facilitate the cleavage reaction.