Question

10 points Hormones work through binding to their specific receptors to induce signaling. Listthe five types of hormone signaling and briefly explain each one * Your answer

Answer 1

Five types of harmone signalling are.

1.G protein coupled receptors.

These receptors have 7 Transmembrane alpha helical structure. Agonist like adrenaline binds to the receptor like Beta receptor .which causes a conformational change and permits interaction of G protein binding site with stimulatory G protein.which binds to GTP in place of GDP.and activates enzyme adenyl cyclase located on inside of membrane. ATP is converted into cAMP which activates protein kinase and other downstream signalling pathway.

2.ion channel receptors.

Agonists bind to receptor like nicotinic cholinergic ,GABA and directly opens ion channels for Na , K , Ca etc.

3.Transmembrane enzyme linked receptors.

This is used by peptide harmone like insulin .it has extracellular and intracellular domains .when insulin binds to extracellular domain , the recetors move laterally and form diamers.Dimerization activates tyrosine kinase activity of intracellular domains so that they phosphorylate tyrosine residues on each other and other proteins which perform downstream signalling function.

4.Transembrane JAK STAT binding receptors.

When agonist binds on outside, the intracellular domain increases affinity for tyrosine protein Janus kinase which gets activated and phosphorylates tyrosine residues .which binds to STAT signal transducer and activator of transcription.which dimerize and enters nucleus and regulate gene transcription. Eg cytokines growth harmone.

5.Receptors regulating gene expression(transcription factors, Nuclear receptors).

Agonist like glucocorticoid penetrates cell membrane and binds to cytosolic receptor called glucocortoid receptor protein. Which leaves HSP and dimerization occurs . This diamer enters nucleus and binds with coactivators and interacts with specific DNA sequences . Specific mRNA is produced and translated into protein, which modifies cell function.