Final answer:
A surface protein, often a glycoprotein, is responsible for recognizing specific host cells in viruses. Glycoproteins facilitate attachment to host cells by interacting with cellular receptors, critical for initiating viral infection. These proteins are key to viral specificity and virulence.
Step-by-step explanation:
The viral structure responsible for recognizing specific host cells is a surface protein, often a glycoprotein. These proteins enable the virus to attach specifically to host cells through interactions with cellular receptors. In the context of the accompanying information and the question, glycoproteins are the components on the virus's surface that interact with the host cell's surface molecules, which are crucial for the initial stages of viral infection.
Viruses have a basic structure consisting of a nucleic acid core (either DNA or RNA) surrounded by a capsid, which is made up of protein subunits. Some viruses, including retroviruses like HIV, have an additional layer known as the viral envelope, derived from the host's membrane structures. Glycoproteins embedded in this envelope play a key role in the specificity of viral infection.
For example, the HIV virus uses glycoproteins to bind to CD4 cells in the human immune system. This specificity is one reason why viruses can only infect certain cell types or organisms. These glycoprotein molecules function as virulence factors, allowing the pathogen to attach and enter the host cells, initiating infection.