Origin-of-life evidence: Which observation supports the idea that primitive life predated both DNA and protein enzymes?

Introduction / Context:
The “RNA world” hypothesis proposes that early life relied on RNA for both information storage and catalysis before the evolution of DNA genomes and protein enzymes. Evaluating the evidence behind this idea is a common concept in molecular evolution.

Given Data / Assumptions:

• Question asks for evidence that primitive life lacked DNA and enzymes.
• Modern biochemistry shows RNA molecules (ribozymes) can catalyze reactions.
• Ribosomal RNA actively catalyzes peptide bond formation.

Concept / Approach:
RNA can serve dual roles: genetic template and catalyst. Laboratory-selected ribozymes exhibit polymerase, ligase, and peptidyl transferase-like activities. This dual capacity supports a phase where RNA alone sustained heredity and metabolism.

Step-by-Step Solution:

Verification / Alternative check:
Ribosomes are ribozymes (the peptidyl transferase center is rRNA). Self-splicing introns and hammerhead ribozymes further confirm catalytic RNA.

Why Other Options Are Wrong:

• DNA and enzymes only in advanced cells: false; even bacteria have DNA and enzymes.
• Advanced cells lack RNA: false; all cells use RNA (mRNA, tRNA, rRNA).
• “All of the above”: cannot be correct because the other statements are false.

Common Pitfalls:
Conflating “evidence for RNA world” with statements about absence of DNA/RNA in modern organisms. The hypothesis relies on RNA’s capacities, not on modern cells lacking DNA or RNA.

Final Answer:
RNA can both store genetic information and catalyze chemical reactions