## SARS-CoV-2 Structural Organization ### Correct Statements **Key Point:** SARS-CoV-2 is a positive-sense, single-stranded RNA virus with a genome of ~29.9 kb, making it one of the largest RNA viruses known. **High-Yield:** The spike (S) protein is the primary determinant of host cell tropism and is the main target of neutralizing antibodies and vaccine development. **Clinical Pearl:** The nucleocapsid (N) protein binds to viral RNA and is essential for virion assembly and structural integrity. ### Why Option 4 Is Incorrect **Key Point:** SARS-CoV-2 buds from the **endoplasmic reticulum (ER) and Golgi apparatus**, NOT from the mitochondrial membrane. **High-Yield:** The viral envelope is acquired as the virus exits the ER-Golgi intermediate compartment (ERGIC), incorporating host-derived lipid bilayer with embedded viral glycoproteins (S, E, M proteins). **Mnemonic:** **ERGIC** = **E**ndoplasmic **R**eticulum-**G**olgi **I**ntermediate **C**ompartment — the budding site for SARS-CoV-2 and other coronaviruses. ### Structural Summary Table | Component | Function | Origin | | --- | --- | --- | | Spike (S) protein | ACE2 receptor binding, cell entry | Viral-encoded | | Envelope (E) protein | Ion channel, virulence | Viral-encoded | | Membrane (M) protein | Virion assembly, structural support | Viral-encoded | | Nucleocapsid (N) protein | RNA packaging, virion assembly | Viral-encoded | | Lipid bilayer | Structural envelope | Host cell ER/Golgi | **Warning:** Do not confuse the budding compartment — SARS-CoV-2 does NOT bud from the plasma membrane (like influenza) or mitochondria; it buds intracellularly from the ERGIC.
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