Final answer:
RNA can fold into three-dimensional structures with catalytic activity, allowing it to function as a ribozyme, unlike the more stable and less flexible DNA. Ribozymes are remnants of the ancient RNA world, which are involved in crucial biological processes, and highlights the RNA-first hypothesis for early molecular evolution.
Step-by-step explanation:
The feature of RNA that allows it to function as a ribozyme is its ability to fold into complex three-dimensional structures which can possess catalytic activity. Unlike DNA, RNA can act as an enzyme because of its single-stranded nature, which is much more flexible, allowing it to catalyze a reaction by bringing together substrates, providing appropriate chemical environments, or directly participating in the chemical reaction.
There are no naturally occurring DNA enzymes primarily because DNA is double-stranded and more stable, with less flexibility for folding into catalytically active structures. DNA is also chemically less reactive compared to RNA. The ribosomal Peptidyl Transferase Center, an example of a ribozyme, demonstrates that the enzymatic activity in certain biological processes is carried out by RNA rather than proteins.
Ribozymes are thought to be remnants of an ancient RNA world where RNA molecules performed both genetic information storage and catalytic functions. Over time, the evolution of protein enzymes and the transition to DNA as a more stable genetic material led to the modern DNA-RNA-protein world. The RNA-first hypothesis suggests RNA's role as a self-catalytic molecular precursor to today's biological systems.