Q.1 Coronavirus genome consists of
(A) double-stranded DNA
(B) double-stranded RNA
(C) negative-sense single-stranded RNA
(D) positive-sense single-stranded RNA
The correct answer to the multiple-choice question on the coronavirus genome is (D) positive-sense single-stranded RNA. This genetic makeup defines coronaviruses like SARS-CoV-2 and enables their unique replication strategy.
Correct Answer
Coronavirus possesses a positive-sense single-stranded RNA (+ssRNA) genome, approximately 30 kb in length, which functions directly as mRNA upon host cell entry. This allows immediate translation of viral proteins like replicase without needing an intermediate RNA copy. Examples include SARS-CoV-2 (29.9 kb) and other family members sharing this conserved structure.
Option Explanations
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(A) Double-stranded DNA: Incorrect, as coronaviruses are RNA viruses, not DNA viruses like herpesviruses or adenoviruses that use dsDNA for genome storage and replication.
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(B) Double-stranded RNA: Incorrect; dsRNA genomes occur in reoviruses (e.g., rotavirus), but coronaviruses feature single-stranded RNA without double-stranded segments.
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(C) Negative-sense single-stranded RNA: Incorrect for coronaviruses; negative-sense ssRNA viruses (e.g., influenza, Ebola) require RNA-dependent RNA polymerase to transcribe complementary positive-sense mRNA first.
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(D) Positive-sense single-stranded RNA: Correct; the genome acts as mRNA, encoding structural proteins (S, E, M, N) and non-structural replicase after 5′-UTR and leader sequence.
