Are all functions of a human cell known?
As someone who has dabbled in both biology and programming, I assume you are referring to the theoritical ability  of functional programming to simulate organic behaviour from well defined input. From that point of view, our comprehension of the human cell behaviour is  currently near stone age level.
The astounding diversity of homeostatic and signaling parameters in our body makes a realistic simulation of human cell normal behaviour largely out of reach, so don't even think about patholgic states.

The more data we will acquire, the more precise our simulations will be. Currently, our data acquisition methods are too primitive, and clearly are not deterministic enough to base computed simulations upon them.

Of course, this answer reflects my own opinion, but I dare think that most of my colleagues will adhere to that view.