Explain how the RNA world hypothesis accounts for two major challenges in the origin of life.

IB DP Biology Higher Level (2023 syllabus) — A2.1 Origins of cells · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

The RNA world hypothesis proposes that RNA molecules were the first informational and catalytic polymers in early cells, preceding both DNA and protein-based life.

Model answer (4 marks)

The RNA world hypothesis explains two key problems in the origin of life.
1. Information storage – RNA can store genetic information in its sequence, acting as a hereditary molecule before DNA evolved.
2. Self‑replication – being single‑stranded, RNA can fold and base‑pair with itself, allowing template‑directed copying without protein enzymes.
3. Catalysis – RNA can fold into three‑dimensional structures that act as ribozymes, performing biological catalysis.
4. Chicken‑and‑egg – a single RNA molecule can both carry information and catalyse reactions, resolving the paradox that nucleic acids need proteins to replicate and proteins need nucleic acids to be synthesised.

Examiner tips

Use the exact phrases ‘information storage’, ‘self‑replication’, ‘catalysis’, and ‘chicken‑and‑egg’ as the mark scheme recognises them.
Show the logical link: RNA as both genetic material and catalyst, which solves the paradox.
Keep each point brief – one sentence each – to fit the 4‑mark structure.

Common mistakes

Confusing DNA with RNA as the first hereditary molecule.
Failing to mention the self‑replication mechanism of single‑stranded RNA.
Using vague terms like ‘early life’ instead of the specific challenges listed.

Mark scheme (4 marks)

Challenge 1 — information storage: RNA can store genetic information in its nucleotide sequence, acting as a hereditary molecule before DNA evolved
Challenge 1 — mechanism: because RNA is single-stranded it can fold and base-pair with itself, enabling self-replication / template-directed copying without protein enzymes
Challenge 2 — catalysis: RNA molecules can fold into three-dimensional structures that function as ribozymes / biological catalysts
Resolution of the 'chicken-and-egg' problem: because a single RNA molecule can both carry information and catalyse reactions, it resolves the paradox that nucleic acids need proteins to replicate and proteins need nucleic acids to be synthesised

Key terms in this question

RNA world hypothesis