Which structure allows a virus to recognize and attach to receptors on the host cell

Entry of virus or viral genome into host cell
differs based on type of virus
1. non-enveloped: 
a. most via endocytosis, w/ an endosome enclosing the virus
b. some via viropexis: VAP-receptor binding causes conformational change of capsid leads to hydrophobic portions of capsid creating a core through host cell membrane
2. enveloped
a. fusion w/ cytoplasmic membrane: viral envelope membrane fuses w/ cell membrane, leading to nucleocapsid release into cytoplasm
b. fusion w/ endosomal membrane: endocytosis of virus leads to fusing w/ endosome membrane and release of nucleocapsid into the cell