Unraveling the Origins of Complex Cell Structures

More than 1.5 billion years ago, a pivotal event in evolution occurred when two small cells merged, setting the stage for the emergence of complex life. This merger ultimately led to the formation of various structures within eukaryotic cells, such as the mitochondrion and the nucleus.

Understanding the origin of these structures has long puzzled scientists, but recent advancements shed light on their beginnings. One hypothesis, known as the “mitochondria late” model, suggests that a primitive host cell with internal membranes engulfed an alphaproteobacterium. However, the “mitochondria early” hypothesis proposes a different sequence of events, indicating that the endomembrane system, characteristic of eukaryotic cells, evolved after the alphaproteobacterium entered a relatively simple host cell from the archaea class. This development may have occurred through vesicles released by the ancestral mitochondrion.

The “inside-out” model suggests that the alphaproteobacterium and its archaeal host existed together in a symbiotic relationship, leading to a gradual encapsulation of the bacterium by the host’s protrusions. These protrusions would have held the mitochondrion, leading to the eventual formation of various membrane structures, including the nucleus.

Both models emphasize the mitochondrion’s alphaproteobacterial origin and the role of vesicles in early cellular development. They offer distinct viewpoints on membrane composition and the evolution of cellular structures. Research into vesicles’ functions in modern cells highlights their potential role in the development of organelles. These studies provide insights into early cellular evolution and the emergence of complex structures.