How is the biconcave shape of RBC maintained? Please explain.
Three-dimensional structure of any cell is maintained due to cytoskeleton. Red blood cells have a shape of biconcave disks which is supported by such proteins as spectrin, anchirin and others. The most prominent component of the red cell membrane cytoskeleton, by molecular mass at least, is a fibrous polypeptide called spectrin. Two isoforms of spectrin, alpha (260 kDa) and beta (225 kDa), form a loosely wound helix. The spectrin tetramers are organized into a meshwork that is fixed to the membrane by the protein ankyrin (215 kDa). Ankyrin is itself connected to a transmembrane protein called 'band 3' or anion exchanger protein (90 to 100 kDa). Specific organization of the named proteins contributes to the shape of erythrocytes.