Final answer:
Viral attachment proteins typically bind to glycoproteins on the host cell surface to initiate infection. This specific interaction dictates the host and cell type a virus can infect. HIV, for example, uses the CD4 glycoprotein on T lymphocytes to attach and infect the cell.
Step-by-step explanation:
The receptors to which animal virus attachment proteins usually bind are glycoproteins. Viruses use these glycoproteins on the host cell surface to attach and initiate infection. For instance, HIV engages the CD4 molecule on T lymphocytes, which is a glycoprotein vital for immune system functioning. The specificity of this interaction is crucial as it determines the host and cell type that can be infected by the virus, working somewhat similar to a key specifically fitting into a lock.
The attachment process through glycoproteins is a prerequisite for the viral penetration of the cell membrane, which is essential for the virus to inject its genome and ultimately replicate within the host cell. An illustration of this mechanism can be found in various viruses, such as adenovirus that uses spikes from its capsid, and HIV, which uses glycoproteins embedded in its envelope for host cell attachment.