Cell biology related question

[Biostudent]

Hello everybody....
looking from the cell membrane you find proteins....how can you tell that this protein has been modified and then placed on the membrane or it is just comming to that cell and is about to enter??!!
I was thinking about an answer,, and thought that if modified it must has a carpohydrate residue, or was phosphorylated and by buds it came out of the cell so the structure of protein may tell,,is this correct??
I also thought that incoming protein will have a receptor that it should bind to inorder to enter the cell....at least these are my predictions to this question ,, I think an application like fluorescence to detect the function of each protein or its further location..but the Dr. told me what if the cell is dead or not functioning how could you tell each protein on the plasma membrane if it has come out from that cell or was about to enter....techniques or mechanisms are all welcome...now I am thinking what about bioinformatic???but how I do not know!!!I have not studied this technique I was told that this might be a good technique..
. anyhow I need other predictions you might have ...

[Mrs.Elexica Nixon2010]

thanks for the help u helped me out