A2.1.3 Challenge of explaining the spontaneous origin of cells Notes

Explaining How the First Cells Could Have Formed

1. The spontaneous origin of cells required four key steps:
   1. Catalysis: speeding up reactions.
   2. Self-replication: passing on information.
   3. Self-assembly: forming complex molecules.
   4. Compartmentalization: creating membrane-bound environments.
2. These processes made it possible for non-living chemistry to transition toward living systems, though the exact path remains unconfirmed and difficult to test.

Catalysis: Controlling Chemical Reactions

1. On prebiotic Earth, metal ions, clays, and mineral surfaces likely served as natural catalysts.
2. In modern cells, enzymes (protein catalysts) and ribozymes (RNA catalysts) perform this role precisely.

Self-Replication: The First Inheritable Molecules

1. RNA is thought to have been the first self-replicating molecule because it can:
   1. Store genetic information (like DNA).
   2. Catalyse reactions (as ribozymes).
2. This dual function allowed RNA molecules that replicated more efficiently to persist, a primitive form of natural selection.

Self-Assembly: Building Complex Molecules

1. Once organic monomers (like amino acids, nucleotides, and fatty acids) formed, they needed to assemble into polymers.
2. Prebiotic conditions such as heat, mineral surfaces, drying cycles, and UV radiation could have driven this process.
3. Resulting polymers:
   1. Proteins (from amino acids)
   2. Nucleic acids (from nucleotides)
   3. Polysaccharides and lipids (from simpler precursors)

Compartmentalization: Birth of Protocells

1. For true “cells” to emerge, life’s chemistry had to be separated from the external environment.
2. Lipids naturally self-organize into bilayers, forming vesicles (protocells).
3. Compartmentalization allowed:
   1. Concentration of reactants inside membranes.
   2. Protection from external fluctuations.
   3. A distinct internal environment for controlled chemistry.