Historically, an important strategy for disrupting the adhesion of integrins to their ligands is by using a synthetic peptide that mimics the binding site on the ecm molecule to which the integrin attaches. in the case of fibronectin, the amino acid sequence is arginine-glycine-aspartate (when written using the single letter designation for each amino acid, this sequence becomes rgd). explain why addition of such synthetic peptides would disrupt binding of cells to their normal substratum.