Biochemical Origin of Life - Fourth step: Origin of Colloids, Coacervates and Individuality

• Organic macromolecules in the aqueous medium attracted each other and precipitated as colloidal particles.
• These colloidal particles, called coacervates, contained more than one type of proteins, nucleoproteins and other organic/inorganic molecules in different combinations.
• Protoplasm is also a colloid system, so coacervates are considered analogous to primitive protoplasmic structures.

Diagrammatic representation of first organised cell from coacervate

• Coacervates later became surrounded by a limiting membrane formed by organised molecules of fatty acids (e.g., lecithin and cephalin).
• After membrane formation, various substances accumulated inside the coacervate, giving it internal organisation and structural individuality.
• Membrane formation marks the beginning of clear separation between inside and outside, an important step towards cell-like organisation.

• Coacervates started absorbing organic substances from the surrounding “oceanic soup".
• They behaved as anaerobic heterotrophs: using ready-made organic molecules in the absence of free oxygen.
• They grew in size and showed variability in chemical composition as more substances accumulated inside.
• After reaching an optimum size (related to viscosity), coacervates multiplied by breaking into smaller droplets.

Coacervates are viewed as precursors of the first organisms, linking chemical evolution with biological evolution.

They show:

• concentration of organic molecules.
• primitive boundary (limiting membrane).
• uptake of nutrients, growth and division.

Because of these features, they are considered stepwise intermediates between non-living colloidal systems and true living cells.

• Coacervates originated in primitive oceans as colloidal droplets formed by the aggregation of large organic macromolecules.
• They eventually developed a fatty acid limiting membrane, which established structural individuality and a distinct internal environment.
• Acting as anaerobic heterotrophs, they grew by absorbing ready-made organic substances from the surrounding ocean.
• Upon reaching an optimal size, these droplets multiplied by breaking apart into smaller units.
• They are considered essential prebiotic precursors that bridge the gap between chemical evolution and the first living cells.