What molecule was believed to function as the first enzyme in early life on Earth?

The correct answer identifies RNA molecules as the most likely candidates for the first enzymes in early life on Earth. This understanding is grounded in the RNA world hypothesis, which suggests that RNA was not only a genetic material but also had the capacity to catalyze biochemical reactions, similar to how proteins function as enzymes.

RNA possesses both informational and catalytic roles; it can store genetic information like DNA but is also capable of folding into specific three-dimensional structures, enabling it to catalyze chemical reactions. Certain RNA molecules, known as ribozymes, have been shown to catalyze reactions in modern biological systems, supporting the idea that RNA could have served as the original pricing for enzyme activity. This ability to perform both roles would have been favorable in the primordial conditions of early life where enzymes were necessary for the chemical reactions that sustain life but were not yet formed.

In contrast, DNA primarily serves as a stable repository of genetic information and lacks catalytic activity in its standard form, while proteins, although excellent enzymes, rely on the genetic information housed in nucleic acids for their synthesis. Ribosomes, while essential in the translation of RNA into proteins, do not themselves experience catalytic functions without RNA involvement. This further emphasizes the unique position RNA held as both the genetic material and