Nokea
Identify the incorrect statement in regard to immunoglobulins (Ig)
- A. Are made up of two identical light chains and two identical heavy chains
- B. Cannot recognize conformational antigens on viral particles
- C. Can recognize only exposed epitopes of pathogens
- D. Expressed early during B cell development on the membrane of B cell precursors (pre- B cells)
Correct Answer: B
Rationale: The correct answer is B because immunoglobulins can indeed recognize conformational antigens on viral particles. Immunoglobulins have variable regions that can bind to a wide range of antigen shapes. Choice A is correct as Ig structure consists of two light and two heavy chains. Choice C is incorrect as immunoglobulins can also bind to internal epitopes. Choice D is incorrect as Ig expression starts during the late B cell development stage.
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What outcome would you least expect if the amount of template in a PCR fell significantly below the optimal amount?
- A. non-specific amplification
- B. increased yield
- C. Allelic drop-out (some alleles fail to amplify)
- D. Longer targets amplify poorly or fail
Correct Answer: B
Rationale: The correct answer is B: increased yield. If the amount of template in a PCR falls significantly below the optimal amount, it would be expected to result in a decreased yield rather than an increased yield. The template is essential for DNA amplification in PCR, and a lower amount would lead to fewer copies being produced. Non-specific amplification (choice A) can occur if there is too much template or incorrect primer annealing. Allelic drop-out (choice C) is likely to happen if there is insufficient template present to amplify all alleles. Longer targets amplifying poorly or failing (choice D) is also a common outcome when template concentration is low. Therefore, the least expected outcome would be an increased yield as that goes against the principle of PCR amplification.
Which of these are a type of mutation?
- A. base substitution
- B. translocation
- C. insertion sequences
- D. recombination
Correct Answer: D
Rationale: The correct answer is D: recombination. Recombination is a type of mutation that involves the exchange of genetic material between two DNA molecules. This process can lead to genetic variation and evolution. Base substitution (A) is a point mutation where one base is replaced by another. Translocation (B) involves the movement of a segment of DNA to another location in the genome. Insertion sequences (C) are short segments of DNA that can move within the genome but are not considered a type of mutation. Recombination (D) is the only choice directly related to a type of mutation involving the exchange of genetic material.
Which of the following statements is incorrect?
- A. The gut microbiome composition in obese individuals is altered and shows overrepresentation of less beneficial species
- B. Fecal transplants have been used to treat Clostridium difficile infections
- C. Crohn's disease is considered a disease caused by loss of tolerance to the gut microbiota
- D. The bacterial type III secretion system is used by species of the gut microbiota to inject effector proteins into intestinal epithelial cells and invade them, as observed in Crohn's disease
Correct Answer: D
Rationale: The correct answer is D because the statement incorrectly implies that the bacterial type III secretion system is used by gut microbiota to invade intestinal epithelial cells in Crohn's disease. In reality, Crohn's disease is not directly caused by invasion of gut microbiota into intestinal cells; it is a complex autoimmune condition. The gut microbiota dysbiosis is associated with Crohn's disease, but invasion of epithelial cells is not the primary mechanism. Choices A, B, and C are correct: A highlights the altered microbiome in obesity, B discusses the use of fecal transplants for C. difficile infections, and C mentions Crohn's disease related to issues with gut microbiota tolerance.
Which classification of chemotherapy drugs is cell cycle phase–nonspecific, breaks the DNA helix which interferes with DNA replication, and crosses the blood-brain barrier?
- A. Nitrosureas
- B. Antimetabolites
- C. Mitotic inhibitors
- D. Antitumor antibiotics
Correct Answer: A
Rationale: Nitrosureas are cell cycle phase–nonspecific, disrupt DNA replication, and cross the blood-brain barrier.
What is the process called when a specific lymphocyte binds its antigen and proliferates?
- A. Clonal deletion
- B. Clonal selection
- C. Antigen presentation
- D. Cytokine signaling
Correct Answer: B
Rationale: The correct answer is B: Clonal selection. During clonal selection, a specific lymphocyte recognizes its specific antigen, binds to it, and undergoes proliferation to generate a large population of identical cells to combat the antigen efficiently. This process ensures an effective immune response.
Incorrect choices:
A: Clonal deletion - This process involves the elimination of self-reactive lymphocytes to prevent autoimmunity, not the proliferation of antigen-specific lymphocytes.
C: Antigen presentation - This is the process by which antigens are displayed to immune cells for recognition, not the proliferation of lymphocytes.
D: Cytokine signaling - While cytokines play a role in immune responses, they are not directly involved in the proliferation of lymphocytes in response to specific antigens.