The Formation of the C3 Convertase Is a Key Step

question 26

Multiple Choice

The formation of the C3 convertase is a key step in complement activation that occurs in all three complement pathways. This enzyme cleaves C3 in blood plasma, leading to a conformational change in the C3b fragment that exposes its reactive thioester group. The activated C3b is potentially harmful to the host, if it becomes covalently attached to a host cell, rather than to the surface of a pathogen. This deleterious outcome is largely avoided by:

• A) The inability of active C3b to diffuse away in the blood plasma.
• B) The inability of active C3b to covalently attach to the membranes of eukaryotic cells.
• C) The rapid hydrolysis of active C3b in solution, rendering it inactive.
• D) The tight binding of active C3b to the C3 convertase.
• E) The ability of active C3b to recruit phagocytic cells.

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Definitions:

Operant Conditioning

The learning of voluntary behavior through the effects of pleasant and unpleasant consequences to responses.

Unpleasant Stimulus

Any object, event, or situation that is undesirable or discomforting to an individual, often leading to avoidance behavior.

Modeling

The process of learning behavior by observing and imitating others, as proposed in Bandura's social learning theory.

Extinction

The disappearance or weakening of a learned response following the removal or absence of the unconditioned stimulus (in classical conditioning) or the removal of a reinforcer (in operant conditioning).