Mesosomes are folded invaginations in the plasma membrane of bacteria that are produced by the chemical fixation techniques used to prepare samples for electron microscopy. Although several functions were proposed for these structures in the 1960s, they were recognized as artifacts by the late 1970s and are no longer considered to be part of the normal structure of bacterial cells.
Initially, it was thought that mesosomes might play a role in several cellular processes, such as cell wall formation during cell division, chromosome replication, or as a site for oxidative phosphorylation. The mesosome was thought to increase the surface area of the cell, aiding the cell in cellular respiration. This is analogous to cristae in the mitochondrion in eukaryotic cells, which are finger-like protrusions and help eukaryotic cells undergo cellular respiration. Mesosomes were also hypothesized to aid in photosynthesis, cell division, DNA replication, and cell compartmentalisation.
Mesosomes are areas in the cell membrane of prokaryotic (bacterial) cells that fold inward. They play a role in cellular respiration, the process that breaks down food to release energy. In Eukaryotes, the majority of this process occurs in mitochondria. The third, and final, step of cellular respiration (electron transport chain) occurs in the space between the two membranes of the mitochondria. This step is critical to the cell as most of the energy from food is released during this stage. Since Prokaryotes do not contain membrane bound organelles, they need a different approach. Instead, they use the mesosomes as a site for the electron transport chain.