The CHOs are usually attached from a Gal (b 1-3) GalNAc to a Ser or Thr of a protein.
Figure: O-linked Glycoproteins
The blood group antigens (CHOs on cells attached to either proteins or lipids) are examples . The sugars shown as chairs in the figure below are the blood group antigens (in contrast to structures found in many texts). They are attached to a core heterosaccharide (shown as red elipse below) which is connected to either a membrane glycoprotein or glycolipid.
Figure: Blood Group Antigens