How are secretory proteins and membrane molecules synthesized?

Protein synthesis begins in the cell nucleus. A given gene (made of DNA) is activated, and it then creates RNA which travels to the ribosomes of the cell, which are essentially microscopic protein factories. The RNA gives the design of the protein, and the ribosomes create the protein based on that design. The raw material for the proteins, which is amino acids, is already present in the cell's cytoplasm.