Viral envelopes and origin: For enveloped viruses, what is the correct statement about the origin of the envelope and the source of embedded glycoproteins?
-
AThe envelope and the embedded proteins are encoded by the viral nucleic acid
-
BThe envelope is derived from the host but it contains embedded proteins coded by the viral nucleic acid
-
CThe envelope is coded by the viral nucleic acids, but the proteins come from the host's membrane proteins
-
DThe envelope and its embedded proteins are derived entirely from the host's membranes
-
EThe envelope lipids and proteins are both synthesized de novo by the virus
Answer
Correct Answer: The envelope is derived from the host but it contains embedded proteins coded by the viral nucleic acid
Explanation
Introduction / Context: Enveloped viruses acquire a lipid bilayer by budding through host cellular membranes (plasma membrane, ER, or Golgi). However, the viral spikes embedded in this membrane are encoded by the viral genome and are essential for attachment and entry. Distinguishing host contribution (lipids) from viral contribution (glycoproteins) is a core virology concept.
Given Data / Assumptions:
- Envelope = host-derived lipid bilayer obtained during budding.
- Spike proteins = viral gene products targeted to budding sites.
- Single best statement is required.
Concept / Approach: Viral glycoproteins are synthesized on host ribosomes, processed in secretory pathways, and trafficked to membranes where budding occurs. The lipid composition therefore reflects the host membrane; the protein identity reflects viral genetic information. Some host proteins may be incorporated nonspecifically, but the key functional spikes are viral.
Step-by-Step Solution: Separate the origin of lipids (host) and spikes (viral). Evaluate each option for this division of labor. Select the statement that captures host-derived envelope with virus-encoded proteins. Exclude options claiming de novo viral lipid synthesis or wholly host-derived proteins.
Verification / Alternative check: Electron microscopy and biochemical analyses show envelope lipid composition mirrors the host membrane, while viral spikes are immunologically specific to the virus.
Why Other Options Are Wrong: Viruses do not synthesize lipids de novo; spike proteins are not generally host-coded; saying both envelope and proteins are host-derived neglects viral glycoproteins.
Common Pitfalls: Assuming any membrane component must be viral; in reality, viruses hijack host membranes but decorate them with their own proteins.
Final Answer: The envelope is derived from the host but it contains embedded proteins coded by the viral nucleic acid.