Geometry in hormone-receptor interactions

The nicotinic acetylcholine receptor consists of four different yet similar subunits combined in a 2 1 1 1 ratio that form a 250 kD membrane resident complex. The overall disposition of the receptor could be described as five membrane-spanning helical bundles of helices. Upon stimulation with two molecules of acetylcholine the helical bundles move collectively and open up an ion channel through the membrane. The organisation of the open receptor is fairly well known from electron microscopy studies and the channel is colloquially referred 

In conclusion, it appears that hormone-receptor regulated processes, although dependent on chemical messengers, rely primarily on unequal global dispositions of the hormone free and stimulated receptor respectively. Receptor structures are chosen in order to enable a fast presentation of the critical global isomer without having to resort to hard-core chemistry. To achieve this essentially extra-chemical end the particular structures must be able to partake in an isometric transformation and hence adopt a structural disposition in compliance with the requirements called for. 

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