A2.1.5 Spontaneous formation of vesicles by coalescence of fatty acids into spherical bilayers Notes

Early Membranes and the Origin of Life

1. For life to emerge, internal chemistry had to be separated from the external environment.
2. Membranes provide this separation, allowing cells to maintain stable internal conditions (compartmentalization).
3. Before true cells existed, simple vesicles (droplets enclosed by lipid bilayers) could have acted as protocells, protecting and concentrating molecules.

Amphipathic Molecules and Bilayers

1. On prebiotic Earth, amphipathic molecules like fatty acids were likely present in the "soup" of organic compounds.
2. Fatty acids have:
   1. Hydrophilic head: Polar, attracted to water
   2. Hydrophobic tail: Non-polar, repelled by water
3. When placed in water, these molecules naturally arrange to minimize energy:
   1. Polar heads face the water
   2. Non-polar tails cluster together, away from water
4. This makes bilayer formation spontaneous and self-organizing.

Vesicle Formation

1. Amphipathic molecules spontaneously form vesicles (droplets enclosed by lipid bilayers).
2. When vesicles formed, they enclosed surrounding molecules, creating a unique internal environment.
3. The hydrophobic core of the bilayer acts as a barrier, limiting the movement of polar molecules between inside and outside.
4. This allows the internal chemistry to become different from the external environment, a critical requirement for life.

How Vesicles Enabled Life’s Building Blocks

1. Concentration of Molecules: Organic molecules inside the vesicle were concentrated and regulated, increasing the likelihood of interactions and efficient chemical reactions.
2. Catalysis: Catalysts, such as metal ions or primitive enzymes, further enhance reaction rates, allowing the formation of complex molecules.
3. Energy Storage via Gradients: Vesicle membranes allowed the creation of ion gradients, where differences in ion concentration across the membrane stored energy.