Briefly describe the mechanism by which an internal stop-transfer sequence in a protein causes the protein to become embedded in the lipid bilayer as a transmembrane protein with a single membrane-spanning region. assume that the protein has an n-terminal signal sequence and just one internal hydrophobic stop-transfer sequence

The start signal sequence refers to an internal hydrophobic residue that is dissimilar to the signal sequence present at the N-terminal. It associates with the signal receptor particle that combines with the SRP receptor on the membrane. However, unlike the N-terminal signal sequence it is not cleaved.  

The stop-transfer signal is also an internal hydrophobic membrane crossing sequence, which follows the start sequence. As soon the translocation machinery comes in contact with the stop-transfer sequence it gets disassembled, the peptide does not get cleaved, however, the translation takes place spontaneously. In this manner, a single start-stop transfer sequence anchors the protein.  

affects the water bodies: excessive use of fertilizers causes eutrophication. the fertilizers which are used on plants affect the quality of land on which it is used, further causing erosion of soil. the fertilizers used on plants contain harmful chemical fumes which affect the environment.