What are receptors? (20% marks). Discuss the relationship between the properties of a drug and potential receptor response under the following headings: agonists, partial agonists, inverse agonists and antagonists (80% marks)
The description of a receptor was worth 20% thus it was expected that detailed information on the different forms of receptors, their structure, the resultant conformational change when activated and where they are found would be provided for full marks. Most candidates were able to correctly define an agonist, antagonist, partial agonist and inverse agonist. Unfortunately, this was the limit of most answers.
Candidates were expected to provide details of drug or agonist/receptor interaction discussing the terms affinity/intrinsic activity and how different mechanisms of binding and interacting with the receptor alters these terms.
To be clear, that "detailed information on the different forms of receptors, their structure, the resultant conformational change when activated and where they are found" was attributed 20% of the marks, which means it would have needed to be written in two minutes, and given that even the fastest hand writers in the world can produce only about 28 words per minute, the maximum word count for this section would have been 56 words. So, receptors, in a soundbite:
(that's 55 words in total)
For the rest of the 80% of the mark, "the relationship between the properties of a drug and potential receptor response" sounds a lot like a list of definitions, as the examiners gave us headings to that effect, and many would have probably left it at that (which is why "this was the limit of most answers"). But then, we see in the college comments that the stem does not contain all of the examiner's expectations. A discussion of "the terms affinity/intrinsic activity and how different mechanisms of binding and interacting with the receptor alters these terms" was also necessary for a full mark.
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Wyllie, D. J. A., and P. E. Chen. "Taking the time to study competitive antagonism." British journal of pharmacology150.5 (2007): 541-551.
Neubig, Richard R., et al. "International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification. XXXVIII. Update on terms and symbols in quantitative pharmacology." Pharmacological Reviews 55.4 (2003): 597-606.
Kenakin, T. Pharmacologic analysis of drug±receptor interaction 3rd ed. New York: Raven Press, 1997.
Eddy, M. D. "Elements, principles and the narrative of affinity." Foundations of Chemistry 6.2 (2004): 161-175.