How will extra dietary proteins be put to use, and in which tissues?

The extra protein in the diet will be broken down to its component amino acids during the digestion process. Those amino acids will be used for protein synthesis within the body. The uptake of the amino acids into cells will depend on how actively those cells are producing proteins. That is, the uptake of the amino acids is not targeted to specific tissues such as muscle. However, growing muscle cells will increase their protein synthesis. Thus, some of the additional protein will go to building muscles, but the rest will be used by other tissues.