Nokea
Which of the following statements is FALSE regarding B cells?
- A. B cells that recognize high concentrations of antigen (self) in the absence of other signals undergo apoptosis in the bone marrow
- B. Bone marrow stem cells migrate to the thymus and develop into B cells
- C. B cells synthesize antibodies and put them on their cell surface
- D. B cells can undergo class switching and produce a different antibody type
Correct Answer: B
Rationale: B cells develop in the bone marrow, not the thymus. Firstly, hematopoietic stem cells in the bone marrow give rise to B cells. They undergo maturation and selection processes in the bone marrow, not in the thymus. Therefore, choice B is false. On the other hand, choices A, C, and D are correct. A is true because B cells with high affinity to self-antigens undergo apoptosis to prevent autoimmunity. C is true since B cells synthesize antibodies which can be displayed on their surface as B cell receptors. D is true because B cells can undergo class switching to produce different types of antibodies based on the immune response requirements.
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Infectious agents of various ultrastructures can be etiological agents of infectious diseases. Which of the groups named below HAS NO cellular structure, protein synthesizing, enzyme and energy systems?
- A. Viruses
- B. Fungi
- C. Bacteria
- D. Protozoa
Correct Answer: A
Rationale: The correct answer is A: Viruses. Viruses are acellular, meaning they lack cellular structure, protein synthesizing ability, enzymes, and energy systems. They are essentially genetic material (DNA or RNA) enclosed in a protein coat. Fungi (B), bacteria (C), and protozoa (D) are all cellular organisms with protein synthesizing, enzyme, and energy systems. Viruses rely on host cells to replicate and carry out metabolic functions, making them distinct from other groups.
Anticodon is:
- A. Produced during the process of replication
- B. A nucleotide triplet on the molecule of mRNA
- C. A nucleotide DNA triplet defining the amino acid which has a specific sequence on the polypeptide chain during the translation
- D. A nucleotide triplet forming a unit of genetic code in a transfer RNA molecule corresponding to a complementary codon on messenger RNA
Correct Answer: D
Rationale: The correct answer is D because an anticodon is a nucleotide triplet in a tRNA molecule that pairs with a complementary codon on mRNA during translation. Step 1: Anticodons are found in tRNA, not in DNA or mRNA. Step 2: Anticodons specifically bind to codons on mRNA to ensure correct amino acid incorporation into the growing polypeptide chain, making option D the most accurate choice. Option A is incorrect as replication does not involve anticodons. Option B is incorrect because codons, not anticodons, are found on mRNA molecules. Option C is incorrect as it describes a codon on DNA, not an anticodon on tRNA.
When examining a patient with a suspicion of food toxicoinfection, a doctor on duty has detected symptoms characteristic of botulism. The patient named the meals he had eaten the day before. What is the most probable cause of infection?
- A. Homemade canned meat
- B. Custard pastry from private bakery
- C. Sour cream from local dairy factory
- D. Strawberries from suburban vegetable garden
Correct Answer: A
Rationale: The correct answer is A: Homemade canned meat. Botulism is often caused by consuming improperly canned or preserved foods, particularly meats. The spores of the Clostridium botulinum bacteria can grow in anaerobic conditions, such as those found in improperly canned foods, leading to the production of the botulinum toxin. The symptoms of botulism align with those characteristic of the patient's condition.
Explanation of why the other choices are incorrect:
B: Custard pastry from private bakery - Unlikely to be the cause of botulism as this type of food is not typically associated with the growth of Clostridium botulinum.
C: Sour cream from local dairy factory - While dairy products can sometimes be sources of foodborne illness, botulism is not commonly associated with sour cream.
D: Strawberries from suburban vegetable garden - Botulism is not typically transmitted through fresh fruits or vegetables, making this an unlikely source of infection.
Listeria monocytogenes are:
- A. Gram-negative rod-shaped bacteria
- B. Gram-positive spherical bacteria
- C. Gram-positive rod-shaped bacteria
- D. None of the above
Correct Answer: C
Rationale: The correct answer is C: Gram-positive rod-shaped bacteria. Listeria monocytogenes is a Gram-positive bacterium, as it retains the crystal violet stain during the Gram staining process. The bacteria are rod-shaped, not spherical. Choice A is incorrect as Listeria monocytogenes is not Gram-negative. Choice D is incorrect as Listeria monocytogenes does fall under the category of Gram-positive bacteria. The key is to remember the characteristics of Listeria monocytogenes, which are Gram-positive and rod-shaped.
The catarrhal stage of the whooping cough is characterized by:
- A. Decrease in paroxysms of coughing
- B. Subsequent respiratory infection for many months after the onset of pertussis
- C. Uncontrollable coughing followed by a high pitched 'whoop' sound
- D. Mild respiratory symptoms (mild coughing, sneezing or a runny nose)
Correct Answer: D
Rationale: The correct answer is D because the catarrhal stage of whooping cough is characterized by mild respiratory symptoms such as mild coughing, sneezing, or a runny nose. During this stage, the cough may start to worsen but is not yet severe.
A: Incorrect - Decrease in paroxysms of coughing is not seen in the catarrhal stage; it occurs later in the paroxysmal stage.
B: Incorrect - Subsequent respiratory infection for many months after the onset of pertussis is not a characteristic of the catarrhal stage.
C: Incorrect - Uncontrollable coughing followed by a high pitched 'whoop' sound is typical of the paroxysmal stage, not the catarrhal stage.