Question

Glycoprotein spikes protruding from the outer surface of viral envelopes function as _____

1) toxins.
2) factors that bind to host cells.
3) cell lysis factors.
4) factors needed for site specific recombination.

Answer 1

Glycoprotein spikes on viral envelopes serve as factors that bind to host cells, allowing the virus to attach, penetrate, and ultimately replicate inside the host cell. These proteins exploit normal cellular receptors, such as the CD4 molecule used by HIV to infect T lymphocytes.

Step-by-step explanation:

Glycoprotein spikes protruding from the outer surface of viral envelopes function primarily as factors that bind to host cells. These specialized proteins interact with specific receptors on the surface of potential host cells. For instance, HIV utilizes the CD4 molecule found on T lymphocytes as a receptor. This binding is crucial for the virus as it allows the virus to adhere securely to the host cell before penetrating the cell membrane and initiating replication within the cell.

The glycoprotein spikes have evolved to exploit the receptors used by cells for normal physiological operations, essentially tricking the cell into allowing the virus entry. For example, the Influenza virus uses hemagglutinin spikes to bind to sialic acid on host respiratory and intestinal cells, demonstrating a key aspect of viral tropism which is the virus's preference for infecting specific cell types, tissues, or organs.