63 - The RNA Earth Hypothesis (w/ Allison Williams!)
63. The RNA Earth Hypothesis
It’s time to go deeper than the anthropological record. Long before ferns, salamanders, and Sam Raimi, there were precursor molecules that would eventually lead to life. What is the RNA earth hypothesis? How could the complexities of life have started? Let’s learn to be scientifically conversational.
General Learning Concepts
1) Why do people care how earth started?
a. Today’s complexity, yesterday’s molecules: Evolution helps describe how processes occur in today’s cells; this means that the initial molecule used to encode for heredity is an important molecule to understand today’s complexity.
b. The RNA World Hypothesis: According to this hypothesis, RNA stored both genetic information and catalyzed the chemical reactions in primitive cells. Only later in evolutionary time did DNA take over as the genetic material and proteins become the major catalyst and structural component of cells.
2) What are some common theories to how the earth started?
a. Support:
i. RNA molecules are catalysts: RNA molecules are capable of catalyzing auto-reactions. If a reaction included being able to self-replicate, it is likely that such a molecule would undergo natural selection and persist in a population. [2]
ii. RNA molecules store information: RNA molecules, like RNA molecules, are capable of encoding information for other processes. Episode 59 explored RNA further.
iii. RNA folding allows for a myriad of different structures: These structures are diverse and could present many suitable surfaces for reactions with substrate or itself that would not otherwise be possible.
b. Objections:
i. RNA is a complex molecule: It is not clear how a molecule as complex as RNA could have arisen from the prebiotic soup
ii. RNA is easily degraded: To have a world formed from RNA would mean that there was some critical threshold of RNA that was surpassed without natural degradation at high pH values.
3) What are some common things people study about RNA earth today?
4) Fun Tidbits
a. The RNA World Hypothesis does not imply RNA was the first replicating molecule: Instead, it simply claims that the molecule was important prior to our DNA/RNA/protein world that we live in.
b. Who proposed the RNA World Hypothesis: This hypothesis was proposed independently by Carl Woese (defined Archaea, National Medal of Science), Francis Crick (stole research ideas from Rosalind Franklin), and Leslie Orgel (British chemist; he was was elected to NAS) in the 1960s -- decades before the discovery of ribozymes -- and soon after the double-helical structure of DNA was determined.
5) Solicited Questions
a. What is a ribozyme? RNA molecules capable of catalyzing specific biochemical reactions (the discovery of which resulted in a Nobel prize for Tom Cech and Sidney Altman). The first discovered ribozymes were self-cleaving RNA sequences that rejoin their ends. RNA biochemists were capable of developing (did they already exist) ribozymes capable of cutting other RNA molecules and not only themselves.