The membrane attack complex (C5b-9) mediates lysis of microbes by forming pores in membranes. Which statement is correct about this complex?

The membrane attack complex (C5b-9) mediates lysis of microbes by forming pores in membranes. Which statement is correct about this complex?

• A. Opsonizes bacteria
• B. Activates B cells
• C. Lyses microbes by creating holes in the membrane
• D. Inhibits phagocytosis

Answer: (C)

The key idea is that the membrane attack complex (C5b-9) directly destroys target cells by forming pores in their membranes. After C5 is split, C5b binds C6–C9 and assembles into a pore that disrupts membrane integrity. This causes uncontrolled flow of water and ions, leading to osmotic lysis of susceptible microbes, especially certain bacteria with thinner cell walls. Opsonization and phagocytosis are mainly driven by other complement components like C3b, and B-cell activation involves antibodies and other signals, not the pore-forming complex. So the accurate statement is that this complex lyses microbes by creating holes in their membranes.

The key idea is that the membrane attack complex (C5b-9) directly destroys target cells by forming pores in their membranes. After C5 is split, C5b binds C6–C9 and assembles into a pore that disrupts membrane integrity. This causes uncontrolled flow of water and ions, leading to osmotic lysis of susceptible microbes, especially certain bacteria with thinner cell walls. Opsonization and phagocytosis are mainly driven by other complement components like C3b, and B-cell activation involves antibodies and other signals, not the pore-forming complex. So the accurate statement is that this complex lyses microbes by creating holes in their membranes.