The first part of this lecture by Prof. Robert Lefkowitz from Duke University gives us some historical background on the researches on G-protein-coupled receptors (GPCRs). The key characteristics of GPCRs are described, with various experimental methodologies which have been employed in those studies over the past forty years. 

This video would provide anyone with a good introduction. 

From the YouTube channel, ibioseminars - their website is: www.ibioseminars.org.

The part 2 of the lecture describes recent findings on beta-arrestins, which desensitise the receptors, mediate their endocytosis, and initiate signalling cascades. Such discoveries lead to identification of previously unknown kinds of pharmacological agents, which selectively activate receptors to favour particular signalling pathway, initiated either by G-protein or by beta-arrestin; the compounds with such properties are known as biased agonists.