Glyphosate weed killer molecule. Computer model showing the molecular structure of a molecule of the herbicide glyphosate. Glyphosate is a widely used herbicide. 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 weed killer 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. Atoms are represented as spheres and are colour-coded: carbon (black), hydrogen (white), nitrogen (blue), oxygen (red), and phosphorus (yellow) - with the bonds between them as rods.