Nokea
Which of the following statements best characterizes an antibody?
- A. An antibody contains high molecular weight RNA as its basic structure.
- B. An antibody is composed of protein and cannot be distinguished from the albumin fraction of the serum proteins.
- C. An antibody is composed of four identical protein subunits which may be caused to dissociate by treatment with urea.
- D. An antibody contains protein as its major chemical component and its synthesis may be elicited by the administration of a foreign protein or polysaccharide.
Correct Answer: D
Rationale: Rationale for Correct Answer D:
1. Antibodies are composed mainly of proteins, specifically immunoglobulins.
2. Antibodies are synthesized in response to foreign proteins or polysaccharides, known as antigens.
3. This process involves B cells recognizing antigens and producing antibodies.
4. The statement accurately reflects the nature of antibody structure and synthesis.
Summary of Incorrect Choices:
A: Antibodies do not contain RNA as their basic structure; they are primarily composed of proteins.
B: Antibodies can be distinguished from albumin fraction as they have specific functions in the immune system.
C: Antibodies consist of two heavy and two light chains, not four identical protein subunits, and are not typically dissociated by urea.
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What does the presence of carcinoembryonic antigens (CEAs) and α-fetoprotein (AFP) on cell membranes indicate has happened to the cells?
- A. They have shifted to more immature metabolic pathways and functions
- B. They have spread from areas of original development to different body tissues
- C. They produce abnormal toxins or chemicals that indicate abnormal cellular function
- D. They have become more differentiated as a result of repression of embryonic functions
Correct Answer: A
Rationale: The presence of CEAs and AFP indicates that cells have reverted to more immature metabolic pathways, characteristic of cancerous transformation.
Which of the following is NOT a feature of adaptive immunity?
- A. Slow response compared to innate immunity
- B. Highly specific recognition of antigens
- C. Memory function
- D. Present at birth
Correct Answer: D
Rationale: The correct answer is D: Present at birth. Adaptive immunity is not present at birth; it develops over time in response to exposure to pathogens. A: Adaptive immunity has a slower response compared to innate immunity as it requires activation and proliferation of specific immune cells. B: Adaptive immunity is highly specific in recognizing antigens through antigen receptors on T and B cells. C: Adaptive immunity has memory function, allowing the immune system to "remember" previous encounters with specific pathogens for a faster and stronger response upon re-exposure.
Which part of the antibody determines its physiological effects?
- A. Fab fragment
- B. Fc fragment
- C. Variable region
- D. Antigen-binding site
Correct Answer: B
Rationale: The correct answer is B: Fc fragment. The Fc fragment of an antibody determines its physiological effects by interacting with immune cells and other effector molecules. It mediates processes like opsonization, complement activation, and antibody-dependent cell-mediated cytotoxicity. The Fab fragment (A) contains the antigen-binding site but does not directly influence physiological effects. The variable region (C) is part of both the Fab and Fc portions and contributes to antigen specificity but does not solely determine physiological effects. The antigen-binding site (D) is located within the Fab portion and is responsible for binding to specific antigens, not for exerting physiological effects.
Who introduced the concept of discrimination between self and non-self?
- A. Elie Metchnikoff
- B. Louis Pasteur
- C. Paul Ehrlich
- D. Charles Janeway
Correct Answer: C
Rationale: Paul Ehrlich introduced the concept of discrimination between self and non-self through his "horror autotoxicus" theory. He proposed that the immune system can differentiate between harmful non-self antigens and self-antigens. Ehrlich's theory laid the foundation for understanding immune responses and the development of immunology. Metchnikoff focused on phagocytosis, Pasteur on microbiology, and Janeway on innate immunity, not specifically on self vs. non-self discrimination.
Which of the following statements is incorrect about allergic reactions?
- A. They always require a sensitization step during which specific IgE are secreted
- B. Allergens causing hay fever are usually inhaled
- C. Food allergy can cause hives
- D. The current guidelines for preventing peanut allergy in infants is complete avoidance of peanuts and peanut-related products until at least six months of age
Correct Answer: D
Rationale: The correct answer is D because current guidelines actually recommend early introduction of peanuts to prevent peanut allergies, not complete avoidance. This is based on research showing early introduction can reduce the risk of developing peanut allergies. Choice A is correct as sensitization is a key step in allergic reactions. Choice B is correct as inhaled allergens can cause hay fever. Choice C is correct as food allergies can indeed manifest as hives.