In the RNA world hypothesis, proteins replaced RNA primarily to catalyze reactions. Which option best describes the proposed reason?

In the RNA world hypothesis, proteins replaced RNA primarily to catalyze reactions. Which option best describes the proposed reason?

• A. To catalyze reactions
• B. To store genetic information
• C. To act as membranes
• D. To signal cellular processes

Answer: (A)

In this idea, the big point is that proteins offered a much wider and more efficient toolkit for speeding up chemical reactions than RNA could. RNA can act as a catalyst in ribozymes, but its chemistry is limited by having only four nucleotides and a more constrained ability to form diverse active sites. Proteins, made from 20 different amino acids with a broad range of side chains, can use many different chemical strategies—acid-base catalysis, covalent catalysis, metal ion coordination, and finely tuned active sites created by folding. This versatility lets proteins catalyze a far greater variety of reactions, with higher specificity and efficiency, which would support the growth of more complex metabolism. So the proposed reason proteins replaced RNA as catalysts is precisely their superior catalytic versatility. Storing genetic information is a role more closely tied to RNA in the RNA world, and membranes are formed by lipids, not proteins, so those options don’t capture why enzymes became the dominant catalysts. Signaling roles do involve proteins, but that’s a later refinement rather than the primary driver for replacing RNA's catalytic function.

In this idea, the big point is that proteins offered a much wider and more efficient toolkit for speeding up chemical reactions than RNA could. RNA can act as a catalyst in ribozymes, but its chemistry is limited by having only four nucleotides and a more constrained ability to form diverse active sites. Proteins, made from 20 different amino acids with a broad range of side chains, can use many different chemical strategies—acid-base catalysis, covalent catalysis, metal ion coordination, and finely tuned active sites created by folding. This versatility lets proteins catalyze a far greater variety of reactions, with higher specificity and efficiency, which would support the growth of more complex metabolism. So the proposed reason proteins replaced RNA as catalysts is precisely their superior catalytic versatility.

Storing genetic information is a role more closely tied to RNA in the RNA world, and membranes are formed by lipids, not proteins, so those options don’t capture why enzymes became the dominant catalysts. Signaling roles do involve proteins, but that’s a later refinement rather than the primary driver for replacing RNA's catalytic function.