Which body system is mainly affected by Creutzfeldt-Jakob disease?

A. All of these choices are correct: Effective antimicrobial drugs must meet several important pharmacologic and microbiologic criteria to ensure therapeutic success. These include selective toxicity toward microbial cells, minimal harmful effects on human tissues, the ability to remain active in body fluids and tissues, and the capacity to reach the site of infection in effective concentrations. Each listed characteristic contributes to the effectiveness and safety of therapy.

B. do not cause serious side effects in humans: One of the essential principles of antimicrobial therapy is selective toxicity, meaning the drug targets microbial structures or metabolic pathways while minimizing harm to host cells. Antimicrobials should produce manageable adverse effects so that treatment can proceed without causing significant injury to the patient.

C. remains active in body tissues and fluids: For an antimicrobial to be effective, it must maintain adequate stability and activity within physiological environments such as blood, tissues, and extracellular fluids. Drugs that remain stable and active in the body are better able to sustain antimicrobial activity against pathogens.

D. readily delivered to the site of infection: Antimicrobial agents must be capable of reaching the infected tissues in sufficient concentrations to inhibit or destroy the pathogen. Barriers such as poor blood supply and tissue inflammation can limit drug delivery. Effective drugs are able to penetrate these tissues or are administered in ways that ensure adequate distribution.

E. high toxicity against microbial cells: Antimicrobial drugs should exert strong inhibitory or lethal effects on microorganisms by targeting structures such as bacterial cell walls, ribosomes, nucleic acids, or metabolic pathways. Selective toxicity allows pathogens to be eliminated while host cells remain largely unaffected. This is characteristic of effective antimicrobial therapy.

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.