Changes in Genomic DNA

Assume you’re a wizard molecular biologist and you want to alter the nucleotide sequence in the mouse gene that encodes the mRNA for the G-protein Sar-1. By scanning the mouse genome nucleotide sequence you find a long segment of DNA that could be transcribed into an mRNA that would be translated on ribosomes as Sar-1. Within the mRNA is a moderately long sequence of nucleotide codons that specify amino acids such as leucine, valine, isoleucine, glycine, alanine, and phenylalanine. You then make mutations in the gene that change one of the alanines to serine and one of the phenylalanines to tyrosine. You insert this altered DNA into normal mouse cells to replace the normal SAR-1 gene and grow the cells in tissue culture. When you examine these cells by electron microscopy you notice that the cells have very small Golgi apparatuses but unusually large endoplasmic reticulum as compared to normal mouse cells in culture. Explain how the genetic changes you made in the mouse genomic DNA could result in such dramatic changes in these two cytoplasmic organelles.