The analysis of the nitrogenous bases of the nucleic acid of a newly discovered virus showed 20% adenine, 40% guanine, 10% thymine, and 30% cytosine. The viral nucleic acid is most likely
double-stranded DNA.
double-stranded RNA.
single-stranded RNA.
single-stranded DNA.
The Correct Answer is C
A. double-stranded DNA: In double-stranded DNA, Chargaff’s rules apply: adenine pairs with thymine and guanine pairs with cytosine, so the percentages of A and T should be roughly equal, as should G and C. The viral nucleic acid shows 20% adenine and only 10% thymine, and 40% guanine with 30% cytosine, which violates these pairing rules, indicating it unlikely.
B. double-stranded RNA: Double-stranded RNA also follows base-pairing rules, with adenine pairing with uracil instead of thymine, and guanine pairing with cytosine. The unequal proportions of bases in this viral genome (e.g., A ≠ U, G ≠ C) suggest that it is not double-stranded RNA.
C. single-stranded RNA: Single-stranded RNA does not require complementary base pairing between strands, allowing unequal proportions of the four nucleotides. The observed percentages of adenine, guanine, cytosine, and thymine/uracil can vary widely, consistent with the data provided. This pattern supports the conclusion that the viral nucleic acid is single-stranded RNA.
D. single-stranded DNA: While single-stranded DNA does not require base pairing, thymine would still be present rather than uracil. However, the high guanine content (40%) and low thymine (10%) are unusual; still, the presence of thymine rather than uracil suggests that if it were RNA, thymine would be replaced with uracil, making single-stranded RNA more likely.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
A. Yeast: Yeast are single-celled fungi with relatively low resistance to physical and chemical agents. They are susceptible to heat, disinfectants, and antiseptics because they lack specialized protective structures like endospores, making them easier to control compared to more resistant microbial forms.
B. Bacterial endospores: Bacterial endospores are highly resistant, dormant structures formed by certain bacteria such as Bacillus and Clostridium species. They have a tough protective coat, low water content, and metabolic inactivity, which make them impervious to heat, radiation, desiccation, and many chemical disinfectants. Endospores can survive extreme environmental conditions for extended periods, making them the most resistant microbial form.
C. Fungal spores: Fungal spores provide some resistance to environmental stress and disinfectants, but they are significantly less resistant than bacterial endospores. Most fungal spores can be inactivated by standard sterilization techniques such as autoclaving.
D. Protozoan cysts: Protozoan cysts are protective forms that allow protozoa to survive harsh environments, including changes in pH and desiccation. While they are moderately resistant, they are not as impervious to sterilization methods as bacterial endospores.
E. Naked viruses: Naked (non-enveloped) viruses are more resistant than enveloped viruses to detergents and some disinfectants due to the absence of a lipid envelope. However, they are still more susceptible to heat, radiation, and chemical agents than bacterial endospores.
Correct Answer is A
Explanation
A. Breakdown of molecules to release energy: Catabolism involves the enzymatic breakdown of complex molecules such as carbohydrates, lipids, and proteins into simpler molecules like sugars, fatty acids, and amino acids. This process releases energy, which is captured in the form of ATP to fuel cellular activities, making it a fundamental part of metabolism.
B. Building molecules: The synthesis of complex molecules from simpler ones is called anabolism, not catabolism. Anabolic processes, such as protein synthesis or glycogen formation, require energy input rather than releasing energy.
C. DNA replication: DNA replication is a specific cellular process that duplicates genetic material for cell division. While it is essential for cell survival, it is not a catabolic process, as it does not involve the breakdown of molecules for energy production.
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