.M&R:Receptor-Effector Signalling via Proteins

Objectives
To understand how signalling molecules are recognized by cells to evoke an appropriate cellular response.
To understand how activated G protein-coupled receptors initiate a linear sequence of signalling events involving G proteins and enzyme or ion channel effector proteins.
What is signal transduction?
For cells to respond to extracellular signalling molecules (e.g. hormones, neurotransmitters, growth factors, etc….) they must possess the appropriate ‘’receptor’’
Receptors can be intracellular (receptors for steroid and thyroid hormones, etc…), but the majority of extracellular signalling molecules do not readily cross the plasma membrane, therefore, their receptors are located at the cell surface.
Although some receptors can directly alter cellular activity, many require ‘’transduction’’ of the initial ligand binding event via other intracellular signalling components to generate a response, e.g. contraction, secretion, proliferation, differentiation, etc.
There are 3 ‘’superfamilies’’ of cell surface receptor
Ligand-gated (receptor-operated) ion channels (e.g. nicotinic acetylcholine receptors)
Receptors with intrinsic enzymatic activity (receptor tyrosine kinases (e.g. insulin receptor)
G protein-coupled (7TM) receptors (e.g. muscarinic acetylcholine receptors)
Each receptor subtype is specific for one (or a very limited number of chemicals (‘LIGAND’).
Ligand binding activated the receptor, which in turn directly or indirectly brings about a change in cellular activity.