During a routine checkup of a middle aged man's blood sample shows hematocrit of 45% and biconcave red blood cells. Biconcavity of RBCs is a function of which of the following?

The biconcave shape is normal and is not a defect. Normal red blood cells are deformable biconcave disks. Their shape is determined by the external environment of the cell, the metabolic activity of the cell, the nature of hemoglobin, the membrane skeleton, and age of the cell. The red blood cell's durability and flexibility are due to its submembranous protein network, the membrane skeleton. The membrane skeleton consists predominantly of four proteins: spectrin, actin, protein 4.1, and ankyrin (also known as syndein). Spectrin is an extrinsic protein located on the cytoplasmic surface of the membrane. It is long and unusually flexible molecule consisting of two structurally and functionally distinct polypeptide chains. The membrane of the RBC comprises a phospholipid bilayer and an underlying two-dimensional network of spectrin molecules. The composite propeies of the phospholipid bilayer and spectrin network result in the biconcave or discocyte morphology of healthy RBCs and give the membrane its elastic and biorheological propeies. Ref: Medical Biochemistry By N. V. Bhagavan, 2001, Page 164 ; High Yield Histopathology by Dudek, 2010, Page 301