Which of the following forms the C5 convertase in the alternative pathway?

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Multiple Choice

Which of the following forms the C5 convertase in the alternative pathway?

Explanation:
In the alternative pathway, the C3 convertase is C3bBb. If another C3b binds to that complex, it becomes C3bBbC3b, which then acts as the C5 convertase. This enzyme complex cleaves C5 into C5a and C5b, enabling downstream events that lead to MAC formation. The other options don’t fit this pathway: C3bBb alone is the C3 convertase, not the C5 convertase; the classical pathway uses C4b2a3b as its C5 convertase; and C4b2b isn’t the active form used here.

In the alternative pathway, the C3 convertase is C3bBb. If another C3b binds to that complex, it becomes C3bBbC3b, which then acts as the C5 convertase. This enzyme complex cleaves C5 into C5a and C5b, enabling downstream events that lead to MAC formation. The other options don’t fit this pathway: C3bBb alone is the C3 convertase, not the C5 convertase; the classical pathway uses C4b2a3b as its C5 convertase; and C4b2b isn’t the active form used here.

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