Nokea
Which of the following statements is most correct? Immunoglobulin gene rearrangement:
- A. Occurs after transcription of an immunoglobulin gene
- B. Creates a complete V exon in the germline DNA
- C. Creates a complete V exon in the B cell DNA
- D. Both A and B are correct
Correct Answer: C
Rationale: The correct answer is C because immunoglobulin gene rearrangement creates a complete V exon in the B cell DNA. This process happens during B cell development, where segments of V, D, and J gene regions are rearranged to form a functional immunoglobulin gene. This rearrangement occurs before transcription, so option A is incorrect. Option B is incorrect because the V exon is not complete in the germline DNA, but rather created through rearrangement in the B cell DNA. Option D is incorrect as it combines two incorrect statements.
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Which of the following is not required for full activation of a naïve lymphocyte?
- A. Migration into an inflammatory site
- B. Costimulatory signalling
- C. Cytokines
- D. Recognition of specific antigen
Correct Answer: A
Rationale: The correct answer is A. Naïve lymphocytes require activation through recognition of specific antigen, costimulatory signaling, and cytokines. Migration into an inflammatory site is not a requirement for full activation. Naïve lymphocytes can be activated in secondary lymphoid organs where antigen presentation occurs. Migration to inflammatory sites occurs after activation to fight infections.
Epithelial cells at mucosal sites have barrier functions exerted through several mechanisms. These mechanisms do not include:
- A. Secretion of mucins
- B. Secretion of antimicrobial peptides
- C. Phagocytosis of microbes
- D. Tight junctions
Correct Answer: C
Rationale: The correct answer is C: Phagocytosis of microbes. Epithelial cells primarily act as a physical barrier to prevent the entry of microbes. Phagocytosis is a function of immune cells, not epithelial cells. A: Secretion of mucins helps trap pathogens. B: Secretion of antimicrobial peptides aids in defense. D: Tight junctions form a physical barrier between cells. Therefore, phagocytosis is not a direct mechanism exerted by epithelial cells at mucosal sites.
Which disease is an example of Type V hypersensitivity?
- A. Multiple sclerosis
- B. Grave's disease
- C. Rheumatoid arthritis
- D. Type 1 diabetes mellitus
Correct Answer: B
Rationale: The correct answer is B, Grave's disease, for Type V hypersensitivity. In Type V hypersensitivity, antibodies target cell surface receptors, leading to abnormal stimulation or blockage. In Grave's disease, antibodies target the thyroid-stimulating hormone receptor, leading to excessive thyroid hormone production. Multiple sclerosis (A) is an example of Type IV hypersensitivity involving T cell-mediated response. Rheumatoid arthritis (C) is an example of Type III hypersensitivity involving immune complex deposition. Type 1 diabetes mellitus (D) is an example of Type II hypersensitivity involving antibody-mediated destruction of cells.
Before the patient receives a kidney transplant, a crossmatch test is ordered. What does a positive crossmatch indicate?
- A. Matches tissue types for a successful transplantation
- B. Determines paternity and predicts risk for certain diseases
- C. Establishes racial background and predicts risk for certain diseases
- D. Cytotoxic antibodies to the donor contraindicate transplanting this donor’s organ
Correct Answer: D
Rationale: A positive crossmatch indicates the presence of preformed cytotoxic antibodies against the donor, contraindicating transplantation.
Which of the following restriction endonucleases produce fragments with blunt ends?
- A. Sacl
- B. EcoRI
- C. Smal
- D. HindIII
Correct Answer: C
Rationale: The correct answer is C: Smal. Smal is a restriction endonuclease that cuts DNA at specific sequences, producing fragments with blunt ends. Smal recognizes the sequence CCCGGG and cuts between the two C's on both strands, resulting in blunt-ended fragments.
Explanation for incorrect choices:
A: Sacl - Sacl produces sticky ends, not blunt ends.
B: EcoRI - EcoRI produces sticky ends with overhangs.
D: HindIII - HindIII also produces sticky ends with overhangs.
In summary, Smal is the only enzyme among the choices that generates DNA fragments with blunt ends.