PCB 3233 Exam 2 V3 | PCB 3233 Immunology |
Actual Q&A with Rationale (PCB3233 Exam 2) |
University of Central Florida
1. During the process of V(D)J recombination, which enzyme is responsible for adding N-
nucleotides to the joints between gene segments to increase junctional diversity?
A. Terminal deoxynucleotidyl transferase (TdT)
B. DNA Ligase IV
C. Artemis
D. RAG-1/2 complex
Correct Answer: A
Explanation: Terminal deoxynucleotidyl transferase (TdT) is a specialized DNA
polymerase that adds non-templated nucleotides to the V, D, and J junctions. This process
significantly increases the diversity of the CDR3 region in both B and T cell receptors.
Without TdT, the repertoire of antigen receptors would be much less diverse and rely
solely on combinatorial and P-nucleotide diversity.
2. Which molecule is responsible for directing MHC class II molecules to the endocytic vesicles
and preventing the binding of self-peptides in the ER?
A. TAP1/2 transporter
B. Invariant chain (Ii)
,C. Calnexin
D. HLA-DM
Correct Answer: B
Explanation: The invariant chain (Ii) forms a complex with the MHC class II alpha and beta
chains in the endoplasmic reticulum. It physically blocks the peptide-binding groove to
prevent the premature binding of endogenous peptides. Additionally, the invariant chain
contains a targeting signal that directs the MHC class II molecule to the acidified endosomal
compartments for peptide loading.
3. A deficiency in which of the following proteins would lead to a complete lack of MHC class I
expression on the cell surface?
A. HLA-DO
B. CLIP
C. Cathepsin S
D. Beta-2 microglobulin (B2m)
Correct Answer: D
Explanation: MHC class I molecules consist of a polymorphic alpha chain non-covalently
associated with the invariant beta-2 microglobulin. Without beta-2 microglobulin, the
alpha chain cannot fold correctly or be transported to the cell surface. This condition
results in a functional deficit where CD8+ T cells cannot recognize or destroy infected host
cells.
, 4. Which of the following best describes the function of HLA-DM in the exogenous antigen
processing pathway?
A. It catalyzes the removal of CLIP and the loading of high-affinity peptides onto MHC class
II.
B. It transports peptides from the cytosol to the ER lumen.
C. It stabilizes empty MHC class I molecules.
D. It degrades extracellular proteins into small peptides.
Correct Answer: A
Explanation: HLA-DM acts as a molecular chaperone within the MIIC (MHC class II
compartment) to facilitate peptide exchange. It induces a conformational change in MHC
class II that releases the CLIP fragment. This allow high-affinity exogenous peptides to bind
before the complex is exported to the plasma membrane.
5. In the thymus, what is the fate of a developing T cell that fails to recognize the self-
MHC:self-peptide complexes presented by thymic epithelial cells?
A. It undergoes apoptosis due to death by neglect.
B. It undergoes receptor editing to change its TCR.
C. It differentiates into a regulatory T cell (Treg).
D. It is exported to the periphery as a ‘null’ T cell.
Correct Answer: A
Actual Q&A with Rationale (PCB3233 Exam 2) |
University of Central Florida
1. During the process of V(D)J recombination, which enzyme is responsible for adding N-
nucleotides to the joints between gene segments to increase junctional diversity?
A. Terminal deoxynucleotidyl transferase (TdT)
B. DNA Ligase IV
C. Artemis
D. RAG-1/2 complex
Correct Answer: A
Explanation: Terminal deoxynucleotidyl transferase (TdT) is a specialized DNA
polymerase that adds non-templated nucleotides to the V, D, and J junctions. This process
significantly increases the diversity of the CDR3 region in both B and T cell receptors.
Without TdT, the repertoire of antigen receptors would be much less diverse and rely
solely on combinatorial and P-nucleotide diversity.
2. Which molecule is responsible for directing MHC class II molecules to the endocytic vesicles
and preventing the binding of self-peptides in the ER?
A. TAP1/2 transporter
B. Invariant chain (Ii)
,C. Calnexin
D. HLA-DM
Correct Answer: B
Explanation: The invariant chain (Ii) forms a complex with the MHC class II alpha and beta
chains in the endoplasmic reticulum. It physically blocks the peptide-binding groove to
prevent the premature binding of endogenous peptides. Additionally, the invariant chain
contains a targeting signal that directs the MHC class II molecule to the acidified endosomal
compartments for peptide loading.
3. A deficiency in which of the following proteins would lead to a complete lack of MHC class I
expression on the cell surface?
A. HLA-DO
B. CLIP
C. Cathepsin S
D. Beta-2 microglobulin (B2m)
Correct Answer: D
Explanation: MHC class I molecules consist of a polymorphic alpha chain non-covalently
associated with the invariant beta-2 microglobulin. Without beta-2 microglobulin, the
alpha chain cannot fold correctly or be transported to the cell surface. This condition
results in a functional deficit where CD8+ T cells cannot recognize or destroy infected host
cells.
, 4. Which of the following best describes the function of HLA-DM in the exogenous antigen
processing pathway?
A. It catalyzes the removal of CLIP and the loading of high-affinity peptides onto MHC class
II.
B. It transports peptides from the cytosol to the ER lumen.
C. It stabilizes empty MHC class I molecules.
D. It degrades extracellular proteins into small peptides.
Correct Answer: A
Explanation: HLA-DM acts as a molecular chaperone within the MIIC (MHC class II
compartment) to facilitate peptide exchange. It induces a conformational change in MHC
class II that releases the CLIP fragment. This allow high-affinity exogenous peptides to bind
before the complex is exported to the plasma membrane.
5. In the thymus, what is the fate of a developing T cell that fails to recognize the self-
MHC:self-peptide complexes presented by thymic epithelial cells?
A. It undergoes apoptosis due to death by neglect.
B. It undergoes receptor editing to change its TCR.
C. It differentiates into a regulatory T cell (Treg).
D. It is exported to the periphery as a ‘null’ T cell.
Correct Answer: A
