This lecture covers methods to quantify receptor-ligand interactions, including rapid filtration and ligand-binding assays with competition. It discusses the impact of reversible inhibitors on binding sites, equilibrium binding, and the effects of mutations on binding and activation. The presentation also delves into ligand-gated ion channels, isothermal titration calorimetry, and the relationship between ligand binding and cellular effects. The instructor explores the Hill equation, cooperativity, and further reading on drug-target residence time. The lecture concludes with a preview of next week's topic on molecular interactions.