The RNA world: first self-replicating molecules
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Flip to reveal answersWhy does heredity require a self-replicating molecule?
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Question
Why does heredity require a self-replicating molecule?
Answer
Because evolution needs **inherited variation** — information can only be passed on if the molecule carrying it can be **copied**.
Question
Which molecule is the strongest candidate for the first self-replicating molecule?
Answer
**RNA** — the early stage when it did both jobs is called the **RNA world**.
Question
What two things can RNA do that make it special?
Answer
**Store genetic information** (its base sequence is a code) AND **act as a catalyst** (**ribozymes**).
Question
What is a ribozyme?
Answer
An **RNA molecule that acts as a catalyst** — it folds up and speeds up reactions, the way a protein enzyme does.
Question
Why did DNA take over information storage?
Answer
DNA is **double-stranded** → **more stable** and easier to repair → a **lower mutation rate**, so information is kept more reliably.
Question
Why did proteins take over catalysis?
Answer
Proteins are built from **20 amino acids** (vs RNA's **4 bases**) → far more chemical variety → far more **versatile catalysts**.
Question
Give one piece of evidence that RNA came first.
Answer
The **ribosome's catalytic core is a ribozyme (rRNA)** — the protein-building machine is itself run by RNA. (Also: translation uses mRNA/tRNA/rRNA; ATP & NAD are ribonucleotides.)
Question
What is the proposed order of events?
Answer
**RNA world** → **DNA** takes over **information storage** → **proteins** take over **catalysis**.
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