Receptors 2

Question 1

Describe structure and function of ligand gated ion channels.

Answer 1

Transmembrane receptor coupled directly to an ion channel, rapid response (ms). Eg) nicotinic Acetylcholine receptor (nAChR) classic multimeric subunit channel linked receptor, 4 different types of receptor subunit, each spanning the membrane 4 times. ACh binds receptor on alpha subunit, opens channel allowing influx of Na+/K+ ions into channel, causing muscle contraction

Question 2

Describe structure and function of tyrosine kinase-linked receptors.

Answer 2

Bound by many growth factors and hormones, EC domain has recognition site. IC domain contains a kinase catalytic domain, tyrosine kinase phosphorylates the tyrosine aa in proteins. Signal transduction involves ligand-induced dimerization of receptors followed by autophosphprylation of tyrosine residues, which act as acceptors for specific domains (SH2) of intracellular proteins involved in the regulation of cell function. Adapter proteins link signalling molecules together without doing any signalling themselves.

Question 3

Describe the structure and function of intracellular receptors.

Answer 3

Mainly cytosolic proteins, must pass through the membrane, slower acting (hours-days). stimulate the transcription of selected genes leading to synthesis of a particular protein and production of a cellular effect. Lipophilic ligands

Question 4

Compare signalling cascade for the four receptor families.

Answer 4

GPCR: binds ligand extracellularly, activates alpha subunit of g protein which acts on effector to produce secondary messengers (cAMP, DAG, IP3) which carry out intracellular functions. eg)adenylate cyclase and phospholipase C

Ligand-gated ion channels: bind ligand extracellularly or intracellularly and open rapidly to allow exchange of ions across the membrane eg)nAChR and GABA

Tyrosine kinase linked receptors: bind ligand extracellularly, dimerize, and autophosphorlyate tyrosine residues which serve as binding sites for signalling molecules inside the cell. eg) extracellular growth factor receptor

Intracellular receptors: lipophilic ligands bind cytosolic receptor proteins to stimulate transcription of target gene depending on ligand. eg) glucocorticoid receptor