Looking at this structure, I would say this molecule has 5 chiral carbons, however it's IUPAC name: (3R,4R,5S,6R)-3-Amino-6-(hydroxymethyl)oxane-2,4,5-triol would suggest only four. Which is it? 

[![Glucosamine][1]][1]


  [1]: https://i.sstatic.net/0JN7g.png