Tuberculosis can be treated by means of combined chemotherapy that includes substances with different mechanisms of action. What antituberculous medication inhibits transcription of RNA into DNA in mycobacteria?

Correct Answer: A

Rationale: Rifampicin is the correct answer because it inhibits RNA transcription in mycobacteria by binding to the bacterial RNA polymerase. This prevents the synthesis of RNA, leading to the inhibition of protein production essential for bacterial growth. Isoniazid inhibits mycolic acid synthesis, Streptomycin inhibits protein synthesis, and Ethionamide disrupts mycolic acid synthesis. These mechanisms are different from inhibiting RNA transcription, making them incorrect choices.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Warts are caused by human papillomavirus (HPV) due to its ability to infect the skin. 2. HPV infects the top layer of skin and causes the rapid growth of cells, leading to the formation of warts. 3. Herpesvirus (choice B) causes herpes, not warts. 4. HIV (choice C) weakens the immune system but does not directly cause warts. 5. Varicella-zoster virus (choice D) causes chickenpox and shingles, not warts. Summary: Choice A is correct as warts are primarily caused by HPV, which infects the skin cells. Choices B, C, and D are incorrect as they are associated with different viral infections that do not lead to the development of warts.

Correct Answer: A

Rationale: The correct answer is A: Selective toxicity. Chemotherapy aims to target cancer cells while minimizing harm to healthy cells, known as selective toxicity. This principle is crucial to effectively treat cancer without causing excessive damage to the patient's body. Accumulation in the macroorganism (B) and causing allergies (C) are not fundamental principles of chemotherapy and can lead to harmful side effects. Therefore, the correct answer is A as it aligns with the core objective of chemotherapy.

Correct Answer: A

Rationale: The correct answer is A: Amoxicillin. Amoxicillin is commonly used in combination therapy with metronidazole and bismuth compounds like De-Nol to eradicate Helicobacter pylori infection in children. Amoxicillin targets the bacterial cell wall synthesis, working synergistically with metronidazole to effectively eradicate the infection. Tetracycline (choice B) is not recommended in children under 8 years old due to potential tooth discoloration. Oleandomycin (choice C) is not commonly used for H. pylori infection. Biseptol (choice D) is a combination of sulfamethoxazole and trimethoprim, not typically used for H. pylori eradication.

Correct Answer: B

Rationale: Step 1: Adenoviruses are known to have icosahedral capsids, not helical. Step 2: Helical capsids are typically found in viruses like tobacco mosaic virus. Step 3: Therefore, the statement that adenoviruses have helical capsids is FALSE. Summary: A is incorrect as adenoviruses do not have helical capsids. C is incorrect as there is no situation where adenoviruses have helical capsids. D is incorrect as there is a clear correct answer, which is B.

Correct Answer: A

Rationale: The correct answer is A: nucleic acid and proteins. Viruses consist of genetic material (nucleic acid) surrounded by a protein coat. The nucleic acid carries the viral genetic information, while the proteins form the capsid that protects the genetic material. This combination is essential for the virus to infect host cells and replicate. Lipids (choice B) are not typically part of the main structure of viruses. Lipids are more commonly found in the host cell membrane. Lipids and proteins (choice C) may be present in the viral envelope but are not the main structural components. Proteins and glycoproteins (choice D) are important for viral attachment and entry into host cells but do not constitute the main structural components of viruses.

Correct Answer: B

Rationale: The correct answer is B: Corynebacterium diphtheriae. This bacterium produces a toxin that causes diphtheria by inhibiting protein synthesis, leading to the formation of a pseudomembrane in the throat. Bordetella pertussis causes whooping cough, Streptococcus pyogenes causes strep throat, and Neisseria meningitidis causes meningitis. Corynebacterium diphtheriae is the only bacterium among the choices known to cause diphtheria due to its specific toxin production.

Correct Answer: B

Rationale: The Gram stain differentiates bacteria based on cell wall structure. It classifies bacteria into Gram-positive (purple) and Gram-negative (pink) based on the presence of peptidoglycan in the cell wall. This method helps in identifying the bacterial species and determining appropriate treatment. Option A (Cell shape) is incorrect because the Gram stain focuses on cell wall composition, not cell shape. Option C (Flagella composition) is incorrect as the Gram stain does not assess flagella. Option D (Nutrient requirements) is incorrect as it does not relate to the purpose of the Gram stain.

Correct Answer: A

Rationale: Flagella are the correct answer because they are long, whip-like structures that aid in bacterial movement towards or away from chemical stimuli. They rotate like propellers, allowing the bacterium to navigate its environment. Pili are used for attachment, not movement. Capsules are involved in protection and adherence, not chemotaxis. Fimbriae help in attachment to surfaces, not in movement towards stimuli.