Which complement complex is known as the membrane attack unit?

The correct answer is that the complement complex known as the membrane attack unit is C56789.

This complex is integral to the complement system, which plays a crucial role in the immune response by facilitating the destruction of pathogens. The C56789 complex assembles on the surface of target cell membranes and forms pores, leading to cell lysis. This process occurs when the complement cascade is activated, with C5 being cleaved into C5a and C5b. C5b then associates with C6, C7, C8, and multiple C9 molecules, culminating in the formation of the membrane attack complex (MAC).

The MAC's ability to create transmembrane pores disrupts the osmotic balance of the target cells, which can ultimately lead to cell death, playing a significant role in combating infections. Understanding the specific proteins involved in the membrane attack complex is vital for appreciating how the immune system can directly attack and eliminate pathogens.