Ribozymes

This name was coined when certain RNA molecules were found to have catalytic activity and, therefore, not all molecules with enzyme activity are proteins.

Here we can see an example, belonging to the group of so-called hammerhead ribozymes, since their secondary structure reminds of this shape.
The model consists of two chains: one of RNA, being the ribozyme, and another of DNA, which takes the place of the substrate.

Secondary structure of the ribozyme bound to its substrate:

The ribozyme cuts a phosphodiester bond in the substrate when this is made of ribonucleotides (so it is an RNA); in the model displayed, a single-stranded DNA substitutes for the substrate so that, even though it binds the ribozyme, it is not hydrolysed and so the structure of the ribozyme-substrate complex can be studied.

The parts on a lighter colour are those regions that form hydrogen bonds between their complementary bases (double-helix regions).

Spacefilling, or spheres, model.