Scientifically how does a steak go from red and slimy to dark then to being drier...?

Question

and full of protein fibers?

Answer 1

Uncooked meat has proteins in it, but they are in their native state.

Cooking does 2 things:  it drives out water (like a drier drives water out of clothes) and fat that has melted, and it denatures the protein.  The denatured protein clumps together to give the texture of cooked meat.