PCB 3233 Final Exam V1 | PCB 3233 Immunology |
Actual Q&A with Rationale (PCB3233 Final Exam) |
University of Central Florida
1. Which of the following Toll-like receptors (TLRs) is localized specifically on the cell surface
to recognize bacterial lipopolysaccharide (LPS)?
A. TLR4
B. TLR3
C. TLR7
D. TLR9
Correct Answer: A
Explanation: TLR4 is a crucial pattern recognition receptor that identifies the Lipid A
component of LPS found on gram-negative bacteria. Unlike TLR3 and TLR9 which are
endosomal, TLR4 functions primarily at the plasma membrane to initiate innate immune
responses. Its activation leads to the recruitment of adapter molecules like MyD88 and
TRIF, triggering pro-inflammatory cytokine production.
2. During the processing of endogenous antigens, which protein complex is responsible for
transporting peptides from the cytosol into the lumen of the endoplasmic reticulum?
A. HLA-DM
B. Invariant chain (Ii)
,C. TAP (Transporter associated with antigen processing)
D. Calnexin
Correct Answer: C
Explanation: The TAP1/TAP2 heterodimer is essential for moving degraded cytosolic
peptides into the ER where they can be loaded onto MHC Class I molecules. Without
functional TAP proteins, peptides cannot reach the MHC binding groove, leading to a
deficiency in surface MHC I expression. This pathway is specific to the endogenous MHC
Class I processing route.
3. What is the primary function of the enzyme RAG-1 and RAG-2 during lymphocyte
development?
A. Introducing double-strand breaks at recombination signal sequences (RSS)
B. Adding N-nucleotides to DNA junctions
C. Facilitating isotype switching in B cells
D. Activating somatic hypermutation
Correct Answer: A
Explanation: RAG-1 and RAG-2 are recombinase enzymes that initiate V(D)J
recombination by recognizing specific RSS motifs. They create the double-strand breaks
necessary to begin the shuffling of gene segments for B and T cell receptors. Mutations in
these genes lead to Severe Combined Immunodeficiency (SCID) due to the total lack of
mature lymphocytes.
, 4. Which isotype of antibody is produced as a pentamer and is the first to be secreted during
a primary immune response?
A. IgG
B. IgA
C. IgM
D. IgE
Correct Answer: C
Explanation: IgM is the initial immunoglobulin class produced by plasma cells before class
switching occurs. In its secreted form, it exists as a pentamer held together by a J-chain,
providing ten antigen-binding sites. This high avidity makes IgM extremely effective at
activating the classical complement pathway and neutralizing pathogens early in an
infection.
5. MHC Class II molecules are primarily expressed on which of the following cell types?
A. Professional antigen-presenting cells (APCs)
B. Erythrocytes
C. All nucleated cells
D. Natural Killer cells
Correct Answer: A
Actual Q&A with Rationale (PCB3233 Final Exam) |
University of Central Florida
1. Which of the following Toll-like receptors (TLRs) is localized specifically on the cell surface
to recognize bacterial lipopolysaccharide (LPS)?
A. TLR4
B. TLR3
C. TLR7
D. TLR9
Correct Answer: A
Explanation: TLR4 is a crucial pattern recognition receptor that identifies the Lipid A
component of LPS found on gram-negative bacteria. Unlike TLR3 and TLR9 which are
endosomal, TLR4 functions primarily at the plasma membrane to initiate innate immune
responses. Its activation leads to the recruitment of adapter molecules like MyD88 and
TRIF, triggering pro-inflammatory cytokine production.
2. During the processing of endogenous antigens, which protein complex is responsible for
transporting peptides from the cytosol into the lumen of the endoplasmic reticulum?
A. HLA-DM
B. Invariant chain (Ii)
,C. TAP (Transporter associated with antigen processing)
D. Calnexin
Correct Answer: C
Explanation: The TAP1/TAP2 heterodimer is essential for moving degraded cytosolic
peptides into the ER where they can be loaded onto MHC Class I molecules. Without
functional TAP proteins, peptides cannot reach the MHC binding groove, leading to a
deficiency in surface MHC I expression. This pathway is specific to the endogenous MHC
Class I processing route.
3. What is the primary function of the enzyme RAG-1 and RAG-2 during lymphocyte
development?
A. Introducing double-strand breaks at recombination signal sequences (RSS)
B. Adding N-nucleotides to DNA junctions
C. Facilitating isotype switching in B cells
D. Activating somatic hypermutation
Correct Answer: A
Explanation: RAG-1 and RAG-2 are recombinase enzymes that initiate V(D)J
recombination by recognizing specific RSS motifs. They create the double-strand breaks
necessary to begin the shuffling of gene segments for B and T cell receptors. Mutations in
these genes lead to Severe Combined Immunodeficiency (SCID) due to the total lack of
mature lymphocytes.
, 4. Which isotype of antibody is produced as a pentamer and is the first to be secreted during
a primary immune response?
A. IgG
B. IgA
C. IgM
D. IgE
Correct Answer: C
Explanation: IgM is the initial immunoglobulin class produced by plasma cells before class
switching occurs. In its secreted form, it exists as a pentamer held together by a J-chain,
providing ten antigen-binding sites. This high avidity makes IgM extremely effective at
activating the classical complement pathway and neutralizing pathogens early in an
infection.
5. MHC Class II molecules are primarily expressed on which of the following cell types?
A. Professional antigen-presenting cells (APCs)
B. Erythrocytes
C. All nucleated cells
D. Natural Killer cells
Correct Answer: A
