The instructions for building a protein come from DNA, which is the genetic material found in the nucleus of every cell.

Here's a breakdown of the process:

1. DNA contains genes: Each gene within DNA holds the code for a specific protein.

2. Transcription: The DNA sequence of a gene is copied into a messenger RNA (mRNA) molecule. This process takes place in the nucleus.

3. Translation: The mRNA molecule travels out of the nucleus to the ribosomes in the cytoplasm. Here, the mRNA code is read by ribosomes, and the ribosomes assemble amino acids in the correct order based on the mRNA instructions.

4. Protein Formation: The chain of amino acids folds into a specific 3D shape, forming the functional protein.

Essentially, DNA acts as a blueprint, providing the instructions for building each protein. These instructions are then transcribed and translated into functional proteins, which carry out a wide range of tasks within the cell and the body.