What is the function of TAP1 and TAP2 proteins?

Question 1 of 5

A. To guide the invariant chain out through the Golgi stack B. To transport peptides across the membrane of the ER C. To catalyze the release of CLIP D. None of the above

Correct Answer: B

Rationale: TAP1/2 transport cytosolic peptides into the ER for MHC I loading ; invariant chain and CLIP are MHC II-related.

Question 2 of 5

How do NK cells recognize healthy cells?

A. By recognizing opsonized antigens B. By recognizing MHC I molecules C. By undergoing receptor editing D. By undergoing negative selection

Correct Answer: B

Rationale: NK cells spare healthy cells with MHC I ; opsonization is phagocytic, editing/selection (C, D) are lymphocyte processes.

Question 3 of 5

Substances called the are capable of directly inhibiting DNA synthesis

A. antibodies B. interferons C. complement system D. histamines

Correct Answer: B

Rationale: Interferons inhibit viral DNA/RNA synthesis; antibodies , complement , and histamines have other roles.

Question 4 of 5

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

Correct Answer: C

Rationale: C3b hydrolyzes quickly in solution , preventing host damage; it can diffuse , attach to host cells , or bind convertase but is regulated.

Question 5 of 5

Once expressed on the surface of host cells, an MHC protein remains stably associated with its bound peptide for several days. This highly stable peptide binding behavior is important because:

A. It prevents peptide exchanges on the cell surface, ensuring that peptide:MHC complexes are reliable indicators of the proteins present inside that host cell B. If the MHC protein lost its peptide it would become unstable, and would be rapidly internalized and degraded C. Pathogens would otherwise evade the immune response by making decoy peptides that mimic host cell peptides D. Pathogens would be able to evade the T cell response by making proteases that cleave MHC proteins inducing peptide release

Correct Answer: A

Rationale: Stable binding ensures MHC reflects intracellular proteins; instability occurs, but decoys or proteases are less relevant.

What is the function of TAP1 and TAP2 proteins?

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