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 ["A","B","D"]
Explanation
A. UAA: UAA is one of the three termination codons in the genetic code. During translation, when the ribosome encounters UAA on the messenger RNA, it signals the end of protein synthesis. Release factors bind to the ribosome at this codon, causing the completed polypeptide chain to be released from the ribosome.
B. UAG: UAG is another stop codon, sometimes referred to as the “amber” stop codon. Like other termination codons, it does not code for an amino acid. Instead, it recruits release factors that terminate translation and allow the newly synthesized protein to detach from the ribosome.
C. UUU: UUU is not a stop codon; it is a sense codon that codes for the amino acid phenylalanine. During translation, a tRNA carrying phenylalanine recognizes this codon and adds the amino acid to the growing polypeptide chain. Therefore, it functions in protein elongation rather than termination.
D. UGA: UGA is a stop codon often called the “opal” stop codon. When the ribosome encounters UGA on mRNA, translation stops because there is no corresponding tRNA that carries an amino acid for this codon. Instead, release factors bind and trigger the termination of protein synthesis.
Correct Answer is D
Explanation
A. Genitourinary system: The genitourinary system, including the kidneys, bladder, and reproductive organs, is not primarily affected by Creutzfeldt-Jakob disease (CJD). This disease does not target urinary function or reproductive structures.
B. Digestive system: The digestive system, which includes organs such as the stomach, intestines, liver, and pancreas, is not the main site of pathology in CJD. Gastrointestinal symptoms are generally absent or secondary to systemic decline.
C. Circulatory system: The heart, blood vessels, and blood components are not directly impacted by CJD. Circulatory dysfunction is not a hallmark of the disease, though secondary effects like immobility could influence cardiovascular health.
D. Nervous system: Creutzfeldt-Jakob disease primarily affects the central nervous system. It is caused by prions, misfolded proteins that induce neurodegeneration, leading to rapidly progressive dementia, motor dysfunction, and neurological decline. The brain tissue shows spongiform changes, making the nervous system the main system affected.
E. Respiratory system: The respiratory system is not the primary target of CJD. While respiratory complications may arise late in the disease due to immobility or aspiration, they are secondary consequences rather than a direct effect of the disease process.
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