Which viral component is responsible for determining the specificity of viral attachment to host cells?
Select one:
a. Lipid bilayer of the viral envelope
b. Viral genome
c. Viral enzymes
d. Capsid proteins or envelope glycoproteins
The correct answer and explanation is:
The correct answer is d. Capsid proteins or envelope glycoproteins.
Viral attachment to host cells is a crucial first step in the viral life cycle, and it largely depends on the interaction between viral components and host cell receptors. This specificity is determined by the capsid proteins in non-enveloped viruses or envelope glycoproteins in enveloped viruses.
The capsid is the protein shell that surrounds the viral genome in many viruses, and it can contain surface proteins that are specifically tailored to bind to host cell receptors. In enveloped viruses, which have a lipid bilayer derived from the host cell membrane, the envelope glycoproteins are embedded in the membrane. These glycoproteins are responsible for recognizing and binding to specific receptor molecules on the surface of the host cell.
For example, the hemagglutinin protein of the influenza virus binds to sialic acid receptors on the surface of respiratory epithelial cells, while the spike proteins of the coronavirus SARS-CoV-2 bind to the ACE2 receptors on human cells.
These viral proteins are the determining factors for the virus’s host range and tissue tropism, meaning which species or cell types a virus can infect. The specificity of the receptor-virus interaction ensures that only certain types of cells can be infected by a given virus, influencing its pathogenicity and the course of infection.
The other options listed play different roles in the viral life cycle. The lipid bilayer of the viral envelope provides structural integrity but is not directly responsible for the specificity of cell attachment. The viral genome contains the instructions for making new viral particles, but does not directly interact with host cell receptors. Viral enzymes are involved in processes like replication and maturation, but not in the initial attachment.