Catalytic RNA and Ribozymes
Some RNA molecules fold into shapes that catalyze chemical reactions. Ribozymes demonstrate that RNA can do more than passively store information.
The Investigative Question
Could catalytic RNA have performed enough chemical work to support an early RNA-based living system?
What We Observe
The discovery that RNA can catalyze chemical reactions changed scientific thinking about the origin of life.
RNA sequences can fold into three-dimensional structures, and some of those structures possess catalytic activity.
Scientific Background
Natural ribozymes participate in several biological reactions. Researchers can also use laboratory selection to obtain RNA molecules with new catalytic activities.
One particularly important research goal is an RNA catalyst capable of sufficiently general RNA replication.
Why It Matters
Ribozymes provide a possible bridge between information and function. A sequence can both be inherited and influence chemical reactions through the structure into which it folds.
What Is Known
Catalytic RNA exists in nature and can also be evolved experimentally. Ribozymes can catalyze several kinds of chemical reactions, including reactions involving RNA itself.
What Is Proposed
RNA World models propose that networks of ribozymes carried out primitive replication and metabolic functions before proteins became the dominant biological catalysts.
What Remains Uncertain
No known natural ribozyme provides a complete demonstration of an autonomous primordial RNA organism. Questions remain concerning the origin of useful ribozyme sequences, replication of catalytic RNAs, and cooperation among different functions.
Key Numbers
Ribozymes are RNA molecules whose folded structures catalyze chemical reactions.
Design Relevance
Ribozymes show that information-bearing molecules can acquire chemical function without protein enzymes, an important fact for evaluating origin-of-life proposals.
The remaining design question concerns how the necessary functional sequences and coordinated network arose.
Assessment
Catalytic RNA is experimentally established and provides significant support for an RNA-rich early stage. Moving from individual catalytic RNAs to a self-maintaining, self-replicating system remains a larger problem.