Nokea
What is the role of antibodies in adaptive immunity?
- A. Antigen presentation
- B. Pathogen destruction through phagocytosis
- C. Neutralization, opsonization, and complement activation
- D. Direct killing of infected cells
Correct Answer: C
Rationale: The correct answer is C: Neutralization, opsonization, and complement activation. Antibodies play a crucial role in adaptive immunity by neutralizing pathogens, facilitating their destruction through opsonization, and activating the complement system for pathogen elimination. This is achieved through binding to antigens on pathogens, marking them for destruction by phagocytes, and triggering the complement cascade. Options A, B, and D are incorrect because antibodies do not directly present antigens, perform phagocytosis, or kill infected cells.
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Hfr strains of bacteria:
- A. do not have an 'F' (fertility) factor.
- B. have an 'F' factor plasmid.
- C. have an 'F' factor integrated in the bacterial chromosome.
- D. transfer the genetic information to other bacteria with ow frequency.
Correct Answer: C
Rationale: The correct answer is C because Hfr strains of bacteria have the F factor integrated into their bacterial chromosome. This integration allows for the transfer of genetic material during conjugation. This integration results in a high frequency of genetic information transfer to recipient cells, which is a characteristic of Hfr strains.
Choice A is incorrect because Hfr strains do have the F factor, but it is integrated into their chromosome, not absent. Choice B is incorrect because Hfr strains do not just have an F factor plasmid; it is integrated into the chromosome. Choice D is incorrect because Hfr strains actually transfer genetic information with high frequency, not low frequency.
EcoRI restriction endonuclease reactions produce fragments with
- A. 3' cohesive ends
- B. blunt ends
- C. 5' cohesive ends
- D. none of the options are correct
Correct Answer: C
Rationale: EcoRI recognizes the palindromic sequence GAATTC and cuts between G and A on both strands, producing 5' cohesive ends. Cohesive ends can base-pair with complementary ends, facilitating DNA ligation. Blunt ends (choice B) are produced by enzymes that cut both DNA strands at the same position. Choice A is incorrect as EcoRI produces 5' cohesive ends, not 3' cohesive ends. Choice D is incorrect as EcoRI does produce cohesive ends.
The most abundant class of antibodies produced during a primary immune response is
- A. IgM
- B. IgE
- C. IgA
- D. IgG
Correct Answer: A
Rationale: The correct answer is A: IgM. During a primary immune response, IgM antibodies are the first class produced by plasma cells. IgM is the largest antibody and is effective at agglutinating pathogens. It is later followed by IgG production. IgE is involved in allergic reactions and parasitic infections, not typically produced in large amounts during a primary response. IgA is more abundant in mucosal tissues and secretions.
Which of the following is NOT a feature of T cells?
- A. They recognize three-dimensional structures of a pathogen
- B. Their receptors possess specificity
- C. Their receptors have one antigen-binding site
- D. Their antigen receptors are never secreted
Correct Answer: A
Rationale: The correct answer is A because T cells do not recognize three-dimensional structures of a pathogen. T cell receptors interact with processed antigen fragments presented by MHC molecules on antigen-presenting cells. Choice B is correct because T cell receptors possess specificity for antigens. Choice C is incorrect because T cell receptors have multiple antigen-binding sites. Choice D is incorrect as T cell receptors can be secreted as soluble forms.
Which of the following is not a type of anemia?
- A. Iron deficiency anemia
- B. Sickle cell anemia
- C. Aplastic anemia
- D. Diabetes
Correct Answer: D
Rationale: The correct answer is D: Diabetes. Anemia is a condition characterized by a lack of healthy red blood cells or hemoglobin. Diabetes does not directly cause anemia; it is a metabolic disorder affecting blood sugar levels. Iron deficiency anemia (A) is caused by a lack of iron, sickle cell anemia (B) is a genetic disorder affecting red blood cells, and aplastic anemia (C) is a bone marrow disorder. Therefore, the other choices are types of anemia, while diabetes is not.