1Explain the general mechanism of the 3 classes of cellsurfa

1.Explain the general mechanism of the 3 classes of cell-surface receptors…. Give examples

2.Signal Transduction by G-protein pathways

3.Understand how G-protein are activated and inactivated

Solution

1.G protein coupled receptors -The largest family of cell surface receptors transmit signals to intracellular targets via the intermediary action of guanine nucleotide binding proteins called V protein the G protein receptor are structurally and functionally related proteins characterized by 7 membrane spanning Alpha helix s more than 8000 V protein coupled receptors have been identified including the receptors for many neurotransmitters neuropeptides and peptide hormones in addition the G protein coupled receptors family includes a large number of visitors that always possible for smell and taste.

G proteins consists of three subunits design Ltd all song Beta and Gamma they are frequently called heterotrimeric G proteins the alpha subunit binds guanine and nucleotides which regulates G-protein activity. In the resting state also alpha is bound to GDP in a complex with Beta and Gamma. The activated gtp- bound alpha sub unit then dissociates from beta and gamma which remain together and function as beta gamma complex. Both the active gtb bound Alfa peb unit and the beta Gama Complex then interact with their targets to elicit an intracellular response.

2.Receptor protein tyrosine kinases -this family includes the receptors for most polypeptide growth factors for protein tyrosine phosphorylation has been particularly well studied as signalling mechanism involved in the control of animal cell growth and differentiation.

The first step in signal signalling from most receptor protein tyrosine kinases is ligand induced receptor dimerization some growth factors such as PDGF and NGF, are themselves dimers consisting of two identical polypeptide chains like and induced dimerization leads to autophosphorylation of the receptors the association of these proteins with auto phosphorylated receptors does presents The First step in the intracellular transmission of signals initated by the binding of growth factors to the cell surface.

3. Cytokine receptors and non receptor protein tyrosine kinases this family of receptors includes the receptors for most cytokines and for some polypeptide hormones examples growth hormone

The first step in signalling from cytokinin receptors is thought to be ligand induced receptor dimerization and crops phosphorylation of the associated non receptor protein tyrosine kinases this activated kinases then phosphorylate the receptors providing phosphotyrosine binding site for the recruitment of downstream signalling molecules that contain SH2 domains.