Tyrosine Kinase receptors

A tyrosine kinase receptor can trigger more than 1 signal transduction pathway at once, helping the cell regulate and coordinate many aspects of cell growth and cell reproduction.

A kinase is an enzyme that catalyzes transfer of phosphate groups.

1)Tyrosine Kinase receptor consist of extracellular signal-binding site, an alpha helix spanning the membrane, and intracellular tail containing multiple tyrosines.

2)the binding of a signal molecule(such as a growth factor) causes 2 receptor polypeptides to form a dimer

3)Dimerization activates the tyrosine-kinase region of each polypeptide, each tyrosine-kinase adds phsophate from an ATP molecue. The phosphorylated tyrosine-kinase receptor proteins activate a variety of specific relay proteins which trigger different transduction pathways.


G-Protein Linked receptors

A G-protein Linked receptor is a plasma membrane receptor that works with the help of a G protein.

When GDP is bound to a G protein, G protein is inactive.

When an appropriate signal molecule binds to the extracellular side of the receptor, the receptor is activated and changes shape. It's intracellular cytoplasmic side then binds to an inactive G protein, causing a GTP to displace a GDP. This activates a G protein.

The activated G protein dissociates from the receptor and binds to an enzyme and activates it.

G protein also functions as GTPase enzyme and hydrolyzes the bound GTP to GDP. inactive G protein dissociates from enzyme and is available for reuse.

The GTPase function of G protein allows the pathway to shut down rapidly when signal molecule is no longer present.