Nokea
The discovery of immunoglobulin gene rearrangement helped to explain:
- A. How the number of different immunoglobulins produced by an individual can be far greater than the number of genes in the human genome
- B. How the number of genes in the human genome can be far greater than the number of different immunoglobulins produced by an individual
- C. How thousands of immunoglobulin chains of different sequence may be produced by a single B cell
- D. Both A and C are correct
Correct Answer: A
Rationale: The correct answer is A: How the number of different immunoglobulins produced by an individual can be far greater than the number of genes in the human genome. Immunoglobulin gene rearrangement occurs during B cell development, leading to the generation of a diverse repertoire of antibodies from a limited number of genes. This process allows for the production of a vast array of immunoglobulins through mechanisms like V(D)J recombination. Choice B is incorrect because the gene rearrangement process actually enables a single gene to encode for multiple immunoglobulins. Choice C is partially correct but does not fully capture the significance of gene rearrangement in expanding the diversity of immunoglobulins beyond what the genome would suggest. Choice D is incorrect as it combines a correct statement (A) with an incomplete statement (C).
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What role do the B-complex vitamins play in wound healing?
- A. Decrease metabolism
- B. Protect protein from being used for energy
- C. Provide metabolic energy for the inflammatory process
- D. Coenzymes for fat, protein, and carbohydrate metabolism
Correct Answer: C
Rationale: B-complex vitamins support energy production, which fuels the inflammatory and reparative processes during wound healing.
The basic structure of an antibody molecule is
- A. One light chain and one heavy chain that are covalently linked and form one antigen binding site
- B. Two identical heavy chains and two identical light chains that are covalently linked and form two antigen binding sites
- C. Two identical heavy chains and two identical light chains covalently linked to form one antigen binding site
- D. Two identical light chains that form the antigen binding site and two identical heavy chains that mediate the effector functions of antibodies
Correct Answer: B
Rationale: Rationale for Answer B:
1. Antibody structure consists of two identical heavy chains and two identical light chains.
2. These chains are covalently linked to form the Y-shaped structure of an antibody.
3. Each chain contributes to the formation of antigen-binding sites.
4. Therefore, two identical heavy chains and two identical light chains form two antigen-binding sites.
Summary of Incorrect Choices:
A: Incorrect because it describes only one antigen-binding site formed by one light chain and one heavy chain.
C: Incorrect because it describes one antigen-binding site formed by two identical heavy chains and two identical light chains.
D: Incorrect because it incorrectly describes the roles of light and heavy chains in antibody structure.
Which pathway of the complement system involves properdin, Factor B, and Factor D?
- A. Classical pathway
- B. Alternative pathway
- C. Lectin pathway
- D. Terminal pathway
Correct Answer: B
Rationale: The correct answer is B: Alternative pathway. This pathway involves properdin, Factor B, and Factor D. Properdin stabilizes the C3 convertase complex formed by Factor B and Factor D, leading to the amplification of the complement cascade. The other choices are incorrect because:
A: Classical pathway is initiated by antigen-antibody complexes binding to C1q.
C: Lectin pathway is activated by lectins binding to carbohydrates on pathogen surfaces.
D: Terminal pathway involves the formation of the membrane attack complex.
Identify the correct statement(s). In eukaryotic microorganisms:
- A. mRNA is short-lived (minutes).
- B. a single, circular chromosome is present.
- C. 5s, 16s, and 23s ribosomal RNA's are present.
- D. extrachromosomal DNA can be present.
Correct Answer: D
Rationale: The correct answer is D because extrachromosomal DNA, such as plasmids, can be present in eukaryotic microorganisms. This is true for certain organisms like yeast and some fungi. These DNA molecules are separate from the main chromosomal DNA and can carry additional genetic information.
A: mRNA in eukaryotic microorganisms is not short-lived; it can have varying lifespans depending on the specific mRNA molecule and cellular conditions.
B: Eukaryotic microorganisms typically have multiple linear chromosomes, not a single circular chromosome.
C: While 5s, 16s, and 23s ribosomal RNAs are present in prokaryotic organisms, eukaryotic microorganisms have different types of ribosomal RNA subunits.
Prophylactic measures that are routinely used as early as possible in HIV infection to prevent opportunistic and debilitating secondary problems include administration of
- A. isoniazid (INH) to prevent tuberculosis
- B. trimethoprim/sulfamethoxazole (TMP/SMX) for toxoplasmosis
- C. vaccines for pneumococcal pneumonia, influenza, and hepatitis A and B
- D. varicella-zoster immune globulin (VZIG) to prevent chickenpox or shingles
Correct Answer: C
Rationale: Vaccination protects against preventable infections that can become severe in immunocompromised individuals.