Cells are often imagined as factories that make hundreds of thousands of proteins every single minute. But in these million reactions, cells have to choose the ‘correct’ raw materials to build the intended proteins. Cells have evolved smart mechanisms to ensure this. In this video, we talk about how cells use an enzyme called DTD to select only one kind of amino acid and reject amino acids with the same composition but whose structures are mirror images of each other. In scientific parlance, they are called L and D-amino acids. This video will take you through how DTD ensures proteins are made with only L-amino acids.