The incorrect statement is : Option A : Mature insulin molecule consists of three polypeptide chains-A, B, and C. The mature insulin molecule actually consists of only two polypeptide chains, A and B, which are linked by disulfide bridges. The C-peptide, or chain C, is present in the proinsulin molecule but is removed during the maturation process to produce the active form of insulin. Therefore, statements B, C, and D are correct.