Mesosomes in bacteria are functional unit for -
Lipid storage
Protein synthesis
Respiratory enzymes
carbohydrate breakdown
Mesosomes: These are vesicular convoluted or multilaminated structures formed as invagination of the plasma membrane into the cytoplasm. Mesosomes are of two types--septal and lateral. Mesosomes are analogous to the mitochondria of Eukaryotes and are the principal sites of respiratory enzymes in bacteria.
General Microbiology Pa 1 (History, Microscopy, Stains and Structure and Physiology of Bacteria)