Virus Entry Mechanisms

Overview

This lecture explains the mechanisms by which enveloped and non-enveloped (naked) viruses enter host cells and release their genetic material.

Enveloped viruses use two main entry mechanisms: fusion with the host membrane or endocytosis.
In the fusion method, viral surface proteins ("spikes") bind to host cell receptors.
The viral envelope directly fuses with the host plasma membrane.
The nucleocapsid is released into the cytoplasm, and the nucleic acid separates from the capsid.
In the endocytosis method, viral spikes bind to host receptors and the whole virion is engulfed by the host membrane, forming a vesicle.
The viral envelope fuses with the vesicle's membrane, releasing the nucleocapsid into the cytoplasm.
The capsid is then removed to release viral nucleic acid.

Naked viruses lack an envelope and enter cells only by endocytosis.
The virion is engulfed into an endocytic vesicle by the host cell.
The viral nucleic acid is released from the vesicle, then separates from the capsid for replication.

Enveloped virus — Virus surrounded by a lipid membrane derived from the host cell.
Naked (non-enveloped) virus — Virus lacking a lipid envelope.
Spikes — Viral surface proteins used to attach to host cell receptors.
Nucleocapsid — Protein shell (capsid) enclosing the viral genome.
Endocytosis — Cellular process where substances are taken into the cell by engulfing them in a vesicle.