Antigen recognition occurs at the variable regions of the light and heavy chains on each side of the antibody. Binding to receptors on immune cells occurs through the heavy chains. Each chain is colored in a different color. The chains are held together through disulfide bonds. The antibody structure is from PDB:1IGT. Read more at:
N. R. Gough, Building Better Antibodies. BioSerendipity (6 November 2018) https://www.bioserendipity.com/building-better-antibodies/.