Question at position 17 The MAC consists of a multimeric complex of which of the following proteins that, by their association, forms a pore in the surface of the attacked cell?C6C9C5bC3bC4bSingle choice
A
C6
B
C9
C
C5b
D
C3b
E
C4b

Question

Question at position 17 The MAC consists of a multimeric complex of which of the following proteins that, by their association, forms a pore in the surface of the attacked cell?C6C9C5bC3bC4b

BlackTom AI · Accepted Answer

C9 polymerizes into the pore-forming ring of the membrane attack complex (MAC), so the correct choice is C9.

1. Relevant knowledge points and concepts
- The complement system has three pathways (classical, lectin, alternative) that converge on C5 cleavage.
- C5b initiates assembly of the MAC by sequentially binding C6, C7, C8 and then recruiting multiple C9 molecules.
- The terminal MAC creates a transmembrane channel that disrupts membrane integrity, leading to cell lysis. The pore itself is formed chiefly by polymerized C9 subunits.

2. Step-by-step reasoning process
- A C5 convertase cleaves C5 into C5a (anaphylatoxin) and C5b.
- C5b binds C6 forming C5b6; this complex binds C7 (C5b67), which inserts into the membrane; C8 binds (C5b678) and begins to perturb the membrane.
- Multiple C9 molecules then bind and polymerize around the C5b678 scaffold, creating the transmembrane channel (MAC) that spans the lipid bilayer and allows ion/water flux, causing lysis.

3. Intermediate steps (assembly sequence)
- C5 → C5a + C5b
- C5b + C6 → C5b6
- C5b6 + C7 → C5b67 (membrane-associated)
- C5b67 + C8 → C5b678 (membrane insertion)
- C5b678 + n C9 → C5b678(C9)n (polymerized pore; typically ~10–16 C9 molecules)

4. Why the correct answer is correct
- C9 is the only terminal complement protein that polymerizes into a multimeric ring to form the pore; its repeated subunits constitute the transmembrane channel responsible for lytic activity.

5. Why the other options are incorrect
- C6: binds to C5b as part of the assembly but does not polymerize to form the pore.
- C5b: initiator/scaffold of MAC assembly but is not the multimeric pore-forming subunit.
- C3b and C4b: opsonins involved in earlier complement steps and formation of C5 convertases, not components of the MAC pore.

6. Conclusion
The multimeric pore-forming component of the MAC is C9; this confirms the provided answer (C9).

Question at position 17 The MAC consists of a multimeric complex of which of the following proteins that, by their association, forms a pore in the surface of the attacked cell?C6C9C5bC3bC4bSingle choice

Similar Questions

Question at position 51 To which of the following is MBL MOST structurally similar?C5bNone of the answers are correct.BbC1qC3b

Question at position 40 Which of the following acts as a serine protease that, with cofactors, cleaves C3b and C4b?Factor HMCP (CD46)ProperdinDAF (CD55)Factor I

Question at position 20 Which of the following provides serine protease activity in the classical complement activation pathway?Both C1r and C1s act in the classical pathway.C1rMASP-2None of the answers acts in the classical pathway.C1s

Question at position 14 Of the molecules listed, which can be considered the key molecule in complement pathways?IgMC1C5 convertaseNone of the answers are correct.MBL

Question at position 10 Which of the following complement fixation pathways can be initiated by a soluble C3 convertase?All of the answers are correct.AlternativeNone of the answers are correct.LectinClassical

What is the term for a group of proteins in serum that finish off the work of antibodies to destroy bacteria and other cells?

The complement system refers to:

More Practical Tools for Students Powered by AI Study Helper

Homework AI Solver

Stylized AI Paper Writer

Plagiarism Checker Assistant

Citation AI Academic Writing Tool

In-Class Translation Assistant

AI Note Generator

AI Quiz Answers

Past Exam Questions from University Test Bank

Smart Practice Assistant

Adaptive Practice

Making Your Study Simpler