within the membrane, such R s are called 'membrane bound receptors'(ii)Receptors for thyioid and steroid hormones are called' cytosol 'receptors becau

, aiso called blockers are motecuies which have a close (chemical) rsembiance with the gonist motecule Therpfore, the antagonista, molecule can and do occupy the receptor sits but rhere is some structural drfference also so that post receptor events d not occur ano because of the fact that the rtceptor sitare are now occupied,the agonist moleculest cannot occupy the R sites for example, the acbion of adrenaln (the agonist) is bocked by oropranolot, therefore, propranoloi is a (ß) blocker adrenttn antagomst Srte (i)Receptors which bind the peptided hormonnes are presend on the cell membrane, that is ,they partiy protude in the ECF ard partly remain within the membrane, such R s are called 'membrane bound receptors'(ii)Receptors for thyioid and steroid hormones are called' cytosol 'receptors because they occur either in t he cytosol or on the nucleus Affinty Agrven type of R has affinty for its own ligand Thus R for aöfenalin has afltmty for adrenalin molecules Bindring This (ie,the binding berween the R and Lmolecules)occurs by Van derWalls force (lntermoleculär dttracnon) and hydrogen bonds but not by covafcent Iinkages Recall. the bindnig by covalent linkages resulits in extremely strong oindng (inreversitble & nding) Structure An R has two domains (regions) (i) a ligand binding site . which binds with the ligand,it has alriniry for its specific L and can recognize the L (n) the öfher doman is called the actve site This site is veryi mporant for the post binding events Furthfr this site deitemes whether the L is an agonisl ür jntergoisl and acts accordingly Movement Aftfr binding with the L. the R becomeis RLC (reccptof-ligand complex) and the RLC moves laterally within the cell membtane in case of membrane nound R Without this movfment the post binding events can not occur.