Nokea
The C3 convertase is
- A. An opsonin facilitating the phagocytic process
- B. Part of the Membrane Attack Complex (MAC) that leads to lysis of targets
- C. An enzyme able to cleave C3
- D. An inhibitor of C3b
Correct Answer: C
Rationale: The correct answer is C because the C3 convertase is an enzyme that cleaves C3 into C3a and C3b, an essential step in the complement cascade. This enzyme is crucial for the initiation of both the classical and alternative pathways. Choice A is incorrect as opsonins enhance phagocytosis but are not directly related to C3 convertase. Choice B is incorrect as the MAC is formed by the terminal complement components, not the C3 convertase. Choice D is incorrect as C3b is not an inhibitor but a product of C3 cleavage by the C3 convertase.
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Which enzyme catalyzes the following reaction? Gap 5' - G G-A-T-C-C—3' ⋮ ⋮ ⋮ ⋮ ⋮ 3' - C-C-T-A-G G—5' Gap 5' - G-G-A-T-C-C—3' ⋮ ⋮ ⋮ ⋮ ⋮ 3' - C-C-T-A-G-G—5'
- A. DNA ligase
- B. DNA endonuclease
- C. None of the options are correct
- D. DNA polymerase 1
Correct Answer: A
Rationale: The correct answer is A: DNA ligase. DNA ligase catalyzes the joining of two DNA strands by forming a phosphodiester bond between the 3' hydroxyl of one nucleotide and the 5' phosphate of another. In the given reaction, the enzyme is needed to seal the nick in the DNA strands after the Okazaki fragments have been synthesized during DNA replication.
Explanation of other choices:
B: DNA endonuclease - Endonucleases cleave the phosphodiester bond within a polynucleotide chain, not join two DNA strands.
C: None of the options are correct - This is incorrect as DNA ligase is the correct enzyme for this reaction.
D: DNA polymerase 1 - DNA polymerase synthesizes new DNA strands by adding nucleotides to the 3' end of the growing chain, not joining two DNA strands.
the characteristic of blood types AB is
- A. a general receptor
- B. a general donor
- C. a receptor and donor
- D. neither donating nor receptor
Correct Answer: A
Rationale: The correct answer is A: a general receptor. Blood type AB individuals have both A and B antigens on their red blood cells, making them universal recipients since they can receive blood from all blood types without rejection. This is because they have no antibodies against A or B antigens. The other choices are incorrect because blood type AB individuals cannot be universal donors (choice B) as they have both A and B antigens, not making them suitable for all recipients. They are not both a receptor and donor (choice C) as they can only receive blood from all types, not donate to all. Lastly, they are not neither donating nor a receptor (choice D) since they can receive blood from all types, making them a receptor.
Which of the following cells are 'professional' antigen presenting cells
- A. Neutrophils, dendritic cells, B cells
- B. B cells, T cells, dendritic cells
- C. Macrophages, B cells, dendritic cells
- D. Neutrophils, epithelial cells, dendritic cells
Correct Answer: C
Rationale: The correct answer is C: Macrophages, B cells, dendritic cells. Professional antigen-presenting cells are specialized immune cells that effectively present antigens to T cells. Macrophages, B cells, and dendritic cells are considered professional APCs because they express major histocompatibility complex (MHC) molecules and co-stimulatory molecules, allowing them to effectively activate T cells. Neutrophils and epithelial cells are not considered professional APCs as they have limited ability to present antigens to T cells. B cells and T cells are not APCs themselves, but B cells can act as APCs when they present antigens to T cells in the context of an immune response.
Which of the following is the best dietary advice to maximize the immune function in healthy people?
- A. To include immune-enhancing formulas.
- B. To avoid polyunsaturated fatty acids.
- C. To increase intake of essential fatty acids and omega-3 fatty acids.
- D. To follow a balanced and varied diet.
Correct Answer: D
Rationale: A balanced and varied diet ensures the intake of all necessary nutrients that support optimal immune function.
In a client with AIDS,a CD4 cell count above ______ mm³ would indicate that antiretroviral therapy is being effective.
- A. 250
- B. 1000
- C. 500
- D. 275
Correct Answer: C
Rationale: A CD4 count above 500 mm³ indicates a strong immune response and effective antiretroviral therapy.