Answer:
The correct answer is ''forms a channel in the target cell membrane that causes cytolysis.''
Step-by-step explanation:
The membrane attack complex (MAC) has the essential effect of producing a notable osmotic imbalance in the microorganism that leads to its cytolysis (in Gram-negative bacteria it inserts into the outer membrane, favoring the entry of lysozyme, and in Gram-positive ones insert into the cytoplasmic membrane, destroying the electrochemical gradients). The lytic pathway corresponds to the final reactions of the complement system. It begins when the C5 convertase enzymes formed either in the classical pathway, MBL or the alternative, fix the factor C5 and fragment it into C5a (anaphylatoxin) that passes into the fluid medium and C5b, which binds non-covalently to C3b. The C5b fraction captures C6 and C7 from the fluid phase, forming a stable C5b67 complex with chemotaxic activity and membrane-binding capacity, which when joining the C8 fraction is cytolytic, and acquires the ability to interact with C9 molecules, forming the complex C5b6789. The C9 molecules then undergo conformational changes, enhance and accelerate the penetration of this membrane attack complex (MAC), giving rise to the formation of channels that allow the free exchange of sodium and water with the outside of the cell, causing the consequent osmotic lysis (cytolysis)of the attacked cell, since C9 is structurally homologous to perforin, a protein released by cytotoxic T lymphocytes and NK cells, and which is also responsible for the formation of pores in the membrane of the target cells.