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?

a. When the integrins are bound to RGD peptides, their receptors will be unavailable for binding to FN (or LN), and thus cells will be inhibited from binding to the ECM.
b. When the ECM molecules are bound to RGD peptides, their receptors will be unavailable for binding to FN (or LN), and thus cells will be inhibited from binding to the integrin.
c. When the integrins are bound to RGD peptides, their receptors will be available for binding to FN (or LN), and thus cells will be inhibited from binding to the ECM.
d. When the ECM molecules are bound to RGD peptides, their receptors will be available for binding to FN (or LN), and thus cells will be inhibited from binding to the integrin.