8. If the nucleotide composition (%) of a viral genome is A = 10, U = 20, C = 40 and G = 30, which one of
the following is this genome?
(a) Double stranded RNA (b) Single stranded RNA
(c) Single stranded DNA (d) Double stranded DNA

Viral genomes vary in structure, with nucleotide compositions revealing key details about strandedness and type. Given A=10%, U=20%, C=40%, G=30%, this profile indicates a single-stranded RNA genome due to unequal base pairing and uracil presence.​

Correct Answer

The genome is (b) Single stranded RNA. Uracil confirms RNA, while A ≠ U and C ≠ G show no base pairing typical of single strands.​

Double-Stranded RNA Explanation

Double-stranded RNA (dsRNA) requires complementary strands, so A equals U and C equals G by Chargaff’s rules for RNA. Here, A=10% ≠ U=20% and C=40% ≠ G=30%, ruling out dsRNA.​

Single-Stranded RNA Characteristics

Single-stranded RNA (ssRNA) lacks pairing constraints, allowing unequal bases like A=10%, U=20%. Many viruses, such as picornaviruses, exhibit this asymmetry, matching the given composition perfectly.​

Single-Stranded DNA Analysis

Single-stranded DNA uses T, not U; this genome has U=20%, confirming RNA over DNA. Even if considering T, A ≠ T (no T present) would fit ssDNA poorly, but U eliminates it.​

Double-Stranded DNA Facts

Double-stranded DNA follows A=T and C=G equality. No T appears here, and U indicates RNA, excluding dsDNA entirely.​