Three-dimensional diagram of a merozoite and its core secretory organelles. (A) The sectioned cell highlights the major cellular architecture and organelle repertoire of the invasive merozoite, with dissected organelles listing core molecular constituents of these key invasion-related compartments. Of note, though definition of secretory organelles is limited to dense granules, micronemes, and rhoptries, there is mounting evidence that subpopulations of organelles and subcompartmentalization within organelles (specifically the rhoptries) certainly exist. The rhoptries are divided into three segments, with PfRh1, -2a, -2b, -4, and -5 in the most distal segment and RON2-5 in the next segment. This organization is predicted based on functionality and early release of the PfRh proteins onto the merozoite surface during invasion as opposed to the release of the RON protein complex, but it has not yet been demonstrated definitively (Riglar et al., 2011). The dense granules are released very soon after invasion and include components of a putative protein translocon that is inserted into the parasitophorous vacuole membrane. Ring-infected erythrocyte surface antigen (RESA) is released from dense granules and exported to the infected red blood cell. The body of the rhoptry bulb contains lipids and other proteins involved in forming the parasitophorous vacuole, including RAP1-3 and RAMA. (B) A P. falciparum merozoite in the process of invading a human red blood cell (image courtesy of S. Ralph, University of Melbourne, Melbourne, Australia). Bar, 200 nm.