Question

There are two main types of adrenergic receptor: the alpha and beta-adrenoceptors. Noradrenaline shows slight selectivity for the alpha-receptor, whereas isoprenaline shows selecivity for the Beta-adrenoceptor. Adrenaline shows no selectivity and binds equally well to both the alpha and beta adrenoceptors. Suggest an explanation for these differences in selectivity.

Answer 1

The proteins or enzymes bind to its ligands with high specificity. If we observe the attached structures of isoprenaline, Noradrenaline and Adrenaline, here the Adrenaline is structurally similar to the both isoprenaline and Noradrenaline. So, both alpha- adrenoceptors and beta-adrenoceptors allow the binding of Adrenaline at their active site.   

However, the isoprenaline and Noradrenaline are structurally dissimilar, so isoprenaline cannot bind to alpha-receptor and the Noradrenaline cannot bind to the Beta-adrenoceptor.