PCB 3233 Immunology Exam 3: Chapters 5 & 6 2026 – UCF
1. Which of the following describes the basic structure of the T-cell receptor
(TCR)?
A. A secreted pentameric protein
B. A homodimer of two identical heavy chains
C. A heterodimer consisting of an alpha and a beta chain
D. A single polypeptide chain with four immunoglobulin domains
Answer: C
Rationale: The TCR is a membrane-bound heterodimer composed of an alpha chain and a
beta chain (or gamma and delta chains), each with a variable and constant region.
2. Unlike B-cell receptors (antibodies), T-cell receptors:
A. Undergo somatic hypermutation after activation
B. Are never secreted and exist only in membrane-bound form
C. Recognize intact, native proteins in solution
D. Can bind to carbohydrates and lipids directly
Answer: B
Rationale: TCRs function only as cell-surface receptors and are not secreted as antibodies
are. They also require antigen presentation on MHC molecules.
,3. Which complex of proteins is required for the expression of the TCR on the
cell surface and for signal transduction?
A. CD4 or CD8
B. MHC Class I
C. The CD3 complex
D. B7-1 and B7-2
Answer: C
Rationale: The CD3 complex (gamma, delta, and epsilon chains) along with the zeta chain
is essential for TCR transport to the surface and signaling.
4. MHC Class I molecules primarily present antigens derived from:
A. Intracellular or endogenous proteins in the cytosol
B. Extracellular pathogens taken up by endocytosis
C. Large parasites in the interstitial fluid
D. Complement proteins
Answer: A
Rationale: MHC Class I molecules present peptides derived from proteins synthesized
within the cell (endogenous), such as viral proteins.
5. MHC Class II molecules are primarily expressed on which cell types?
A. All nucleated cells
B. Only red blood cells
C. Professional antigen-presenting cells (APCs)
D. Neurons and muscle cells
Answer: C
Rationale: Professional APCs (dendritic cells, macrophages, and B cells) express MHC Class
II to present exogenous antigens to CD4 T cells.
, 6. The peptide-binding groove of MHC Class I is formed by which domains?
A. Alpha-1 and Beta-1
B. Alpha-1 and Alpha-2
C. Alpha-2 and Beta-2 microglobulin
D. Beta-1 and Beta-2
Answer: B
Rationale: In MHC Class I, the alpha chain folds to form the groove using its alpha-1 and
alpha-2 domains. Beta-2 microglobulin does not form the groove.
7. What is the typical length of a peptide that binds to MHC Class I molecules?
A. 5-7 amino acids
B. Over 30 amino acids
C. 13-25 amino acids
D. 8-10 amino acids
Answer: D
Rationale: MHC Class I grooves are closed at the ends, restricting peptide length to usually
8, 9, or 10 amino acids.
8. MHC Class II molecules bind to which T-cell co-receptor?
A. CD8
B. CD4
C. CD28
D. CD3
Answer: B
Rationale: CD4 molecules on T helper cells bind to the invariant region of MHC Class II
molecules.
1. Which of the following describes the basic structure of the T-cell receptor
(TCR)?
A. A secreted pentameric protein
B. A homodimer of two identical heavy chains
C. A heterodimer consisting of an alpha and a beta chain
D. A single polypeptide chain with four immunoglobulin domains
Answer: C
Rationale: The TCR is a membrane-bound heterodimer composed of an alpha chain and a
beta chain (or gamma and delta chains), each with a variable and constant region.
2. Unlike B-cell receptors (antibodies), T-cell receptors:
A. Undergo somatic hypermutation after activation
B. Are never secreted and exist only in membrane-bound form
C. Recognize intact, native proteins in solution
D. Can bind to carbohydrates and lipids directly
Answer: B
Rationale: TCRs function only as cell-surface receptors and are not secreted as antibodies
are. They also require antigen presentation on MHC molecules.
,3. Which complex of proteins is required for the expression of the TCR on the
cell surface and for signal transduction?
A. CD4 or CD8
B. MHC Class I
C. The CD3 complex
D. B7-1 and B7-2
Answer: C
Rationale: The CD3 complex (gamma, delta, and epsilon chains) along with the zeta chain
is essential for TCR transport to the surface and signaling.
4. MHC Class I molecules primarily present antigens derived from:
A. Intracellular or endogenous proteins in the cytosol
B. Extracellular pathogens taken up by endocytosis
C. Large parasites in the interstitial fluid
D. Complement proteins
Answer: A
Rationale: MHC Class I molecules present peptides derived from proteins synthesized
within the cell (endogenous), such as viral proteins.
5. MHC Class II molecules are primarily expressed on which cell types?
A. All nucleated cells
B. Only red blood cells
C. Professional antigen-presenting cells (APCs)
D. Neurons and muscle cells
Answer: C
Rationale: Professional APCs (dendritic cells, macrophages, and B cells) express MHC Class
II to present exogenous antigens to CD4 T cells.
, 6. The peptide-binding groove of MHC Class I is formed by which domains?
A. Alpha-1 and Beta-1
B. Alpha-1 and Alpha-2
C. Alpha-2 and Beta-2 microglobulin
D. Beta-1 and Beta-2
Answer: B
Rationale: In MHC Class I, the alpha chain folds to form the groove using its alpha-1 and
alpha-2 domains. Beta-2 microglobulin does not form the groove.
7. What is the typical length of a peptide that binds to MHC Class I molecules?
A. 5-7 amino acids
B. Over 30 amino acids
C. 13-25 amino acids
D. 8-10 amino acids
Answer: D
Rationale: MHC Class I grooves are closed at the ends, restricting peptide length to usually
8, 9, or 10 amino acids.
8. MHC Class II molecules bind to which T-cell co-receptor?
A. CD8
B. CD4
C. CD28
D. CD3
Answer: B
Rationale: CD4 molecules on T helper cells bind to the invariant region of MHC Class II
molecules.
