Nokea
Viral antigenic shift
- A. Is caused by multiple random mutations
- B. Is caused by a single mutation
- C. It affects only internal viral proteins not recognized by preexisting antibodies
- D. It refers to the appearance of new HA variants not recognized by preexisting antibodies
Correct Answer: D
Rationale: Step 1: Viral antigenic shift involves major changes in the surface proteins of the virus, particularly the hemagglutinin (HA) protein.
Step 2: These changes result in the emergence of new variants that are not recognized by preexisting antibodies.
Step 3: This process is distinct from antigenic drift, which involves minor changes due to random mutations.
Step 4: Choice D correctly states that viral antigenic shift refers to the appearance of new HA variants not recognized by preexisting antibodies.
Summary: Choice A is incorrect because viral antigenic shift is not caused by multiple random mutations. Choice B is incorrect as antigenic shift involves major changes, not a single mutation. Choice C is incorrect as it affects surface proteins like HA, not just internal proteins.
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Which of the following characteristics do not occur in prokaryotic cells?
- A. cellular organization
- B. thylakoid membranes within chloroplasts
- C. oxygenic photosynthesis
- D. anaerobic respiration
Correct Answer: B
Rationale: The correct answer is B: thylakoid membranes within chloroplasts. Prokaryotic cells lack membrane-bound organelles like chloroplasts, where thylakoid membranes are found. This is a key feature of prokaryotic cells. Choices A, C, and D are characteristics that can occur in prokaryotic cells. Cellular organization is present in prokaryotic cells, oxygenic photosynthesis can be carried out by some prokaryotic organisms, and prokaryotic cells can perform anaerobic respiration.
Which of the following processes does not require the involvement of an antigen-specific T helper cell?
- A. Somatic hypermutation
- B. VDJ gene rearrangement
- C. Immunoglobulin class switching
- D. Memory cell differentiation
Correct Answer: B
Rationale: Correct Answer: B (VDJ gene rearrangement)
Rationale:
1. VDJ gene rearrangement occurs during B cell development in the bone marrow, independent of T helper cells.
2. Somatic hypermutation and immunoglobulin class switching require T helper cell interactions.
3. Memory cell differentiation also involves T helper cells for activation and differentiation.
4. Therefore, VDJ gene rearrangement is the only process not directly dependent on antigen-specific T helper cells.
Defensins are
- A. Cationic antimicrobial peptides
- B. Opsonins
- C. DAMPs
- D. Fatty acids
Correct Answer: A
Rationale: Defensins are cationic antimicrobial peptides that play a crucial role in the innate immune system by disrupting the microbial cell membrane. This property allows them to kill a wide range of pathogens. Option A is correct because it accurately describes the primary function of defensins.
Option B, opsonins, are proteins that enhance phagocytosis but are not specific to defensins. Option C, DAMPs, are damage-associated molecular patterns released by damaged cells and are not related to defensins. Option D, fatty acids, are not directly related to the antimicrobial properties of defensins.
Which of the following bacteria are individuals with complement deficiencies more susceptible to?
- A. Escherichia coli
- B. Haemophilus influenzae
- C. Staphylococcus aureus
- D. Mycobacterium tuberculosis
Correct Answer: B
Rationale: Individuals with complement deficiencies are more susceptible to encapsulated bacteria. Haemophilus influenzae is an encapsulated bacterium, making it the correct choice. The complement system plays a crucial role in opsonization and killing of encapsulated bacteria. Escherichia coli (choice A) is not an encapsulated bacterium, so complement deficiency doesn't significantly increase susceptibility. Staphylococcus aureus (choice C) and Mycobacterium tuberculosis (choice D) are also not encapsulated bacteria, therefore complement deficiencies do not have a direct impact on susceptibility to these pathogens.
Which complement components are primarily involved in Type III hypersensitivity?
- A. C1 and C4
- B. C3a and C5a
- C. C5b and C6
- D. C2 and C7
Correct Answer: B
Rationale: The correct answer is B: C3a and C5a. In Type III hypersensitivity reactions, immune complexes form and deposit in tissues, leading to complement activation. C3a and C5a are anaphylatoxins released during complement activation, causing inflammation and tissue damage in Type III hypersensitivity.
Rationale:
A: C1 and C4 are primarily involved in Type I hypersensitivity reactions.
C: C5b and C6 are part of the membrane attack complex in the classical pathway of complement activation, not specific to Type III hypersensitivity.
D: C2 and C7 are involved in the classical pathway of complement activation but not directly implicated in Type III hypersensitivity reactions.