Glyphosate weedkiller, molecular model. Glyphosate is a widely used herbicide, the most common brand being Roundup. It kills weeds by inhibiting their ability to make the amino acids phenylalanine, tyrosine and tryptophan. These amino acids are the building blocks for the proteins that plants need to survive. This weedkiller is popular because it has very little effect on animals, as they do not make these amino acids in their bodies but obtain them from their diet. This molecule has the chemical formula C3H8NO5P. Atoms are represented as spheres and are colour coded: carbon (C, grey) hydrogen (H, white), nitrogen (N, blue), oxygen (O, red) and phosphorus (P, orange).