Nokea
Which complement pathway is triggered by mannose-binding lectin (MBL)?
- A. Alternative pathway
- B. Classical pathway
- C. Lectin pathway
- D. Terminal pathway
Correct Answer: C
Rationale: The correct answer is C, Lectin pathway. MBL recognizes pathogen-associated molecular patterns containing mannose, initiating the lectin pathway. MBL binds to mannose on microbial surfaces, activating MBL-associated serine proteases, leading to the formation of the C3 convertase. This triggers the rest of the complement cascade.
A: Alternative pathway is triggered by spontaneous hydrolysis of C3, not by MBL.
B: Classical pathway is activated by antigen-antibody complexes, not MBL.
D: Terminal pathway (also known as the membrane attack complex) is the final step of all complement pathways, not specifically triggered by MBL.
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Attenuated vaccines can be obtained by
- A. Passage through cultured cells
- B. Formaldehyde treatment
- C. The use of viral vectors carrying pathogen subunits
- D. All of the above treatments would lead to attenuated vaccines
Correct Answer: A
Rationale: The correct answer is A: Passage through cultured cells. Attenuated vaccines are produced by weakening the pathogen through serial passages in cultured cells, reducing virulence while maintaining immunogenicity. Formaldehyde treatment (B) disrupts the pathogen's structure and is used for inactivated vaccines. The use of viral vectors carrying pathogen subunits (C) is a method for creating subunit vaccines, not attenuated vaccines. Therefore, D is incorrect as not all treatments lead to attenuated vaccines.
Which of the following is an example of a live attenuated bacterial vaccine?
- A. Cholera
- B. Typhoid
- C. Anthrax
- D. Plague
Correct Answer: B
Rationale: The correct answer is B: Typhoid. Live attenuated vaccines contain weakened forms of the pathogen that can replicate in the host to stimulate a strong immune response without causing disease. Typhoid vaccine is an example of a live attenuated bacterial vaccine because it contains weakened Salmonella typhi bacteria. Cholera (A), Anthrax (C), and Plague (D) vaccines are not live attenuated bacterial vaccines; they are either killed/inactivated or subunit vaccines. Live attenuated vaccines provide longer-lasting immunity compared to other vaccine types.
What is the lag phase of the primary antibody response?
- A. 1-3 days
- B. 5-10 days
- C. 10-15 days
- D. No lag phase
Correct Answer: B
Rationale: The lag phase of the primary antibody response refers to the time it takes for the immune system to generate specific antibodies after initial exposure to an antigen. The correct answer is B (5-10 days) because during this period, B cells are activated, undergo proliferation, differentiate into plasma cells, and start producing antibodies. This process takes time as the immune system needs to recognize the antigen, mount a response, and produce sufficient antibodies. Option A (1-3 days) is too short for the full activation and differentiation of B cells. Option C (10-15 days) is too long for the typical lag phase duration. Option D (No lag phase) is incorrect because there is always a lag phase before the peak antibody production in the primary immune response.
DNA ligase catalyzes reactions that facilitate the formation of
- A. ester bonds
- B. DNA ligase
- C. phosphohydroxyl bonds
- D. amide bonds
Correct Answer: B
Rationale: DNA ligase catalyzes the formation of phosphodiester bonds between the sugar-phosphate backbone of DNA strands. The correct answer is B because DNA ligase specifically acts on these phosphodiester bonds to seal nicks in the DNA molecule during processes like DNA replication and repair. Option A, ester bonds, are not formed by DNA ligase. Option C, phosphohydroxyl bonds, is not a recognized type of bond in DNA ligation. Option D, amide bonds, are not formed by DNA ligase either. Thus, the correct answer is B as it aligns with the known function of DNA ligase.
Which of the following lymphoid tissues has both hematopoietic and immune functions and acts as an emergency reservoir of blood and filters the blood as well?
- A. Tonsils and adenoids
- B. Thymus gland
- C. Spleen
- D. Lymph nodes
Correct Answer: C
Rationale: The spleen has both hematopoietic and immune functions acting as a blood filter and reservoir and plays a key role in removing old or damaged red blood cells.