Extracellular receptor signalling pathways 1

Outline the process of cell signal transduction

Stage 1: an extracellular signal molecule activates a membrane receptor

Stage 2 : signa transduced via a specific pathway

Stage 3 : activates a response

First messenger

Extracellular signal

Second messenger system

Intracellular molecules

Transducers

Proteins that convert the message of extracellular signals into intracellular messenger molecules that trigger a response

Give examples of response to cell signal transduction.

See highlighted

What is the benefit of having an amplified response ?

One small signal can produce a large effect

Examples of molecules that act as extracellular signalling molecules

Amines, peptides and proteins, steroids, other small molecules e.g amino acids, ions and gases

What are the 4 main classes of receptors ?

1. Ligand gated ion channels

2. G-protein coupled receptors

3. Enzyme-linked receptors

4. Nuclear receptors

What is a Ligand-gated ion channel ?

An ion channel that is mediated by a signal molecule. Upon activation allows ions to flow through it

Explain how a ionotropic receptor is a ligand gated ion channel ( Nicotinic acetylcholine receptor )

Ligand gated ion channel that is mediated by acetylcholine (and nicotine)

Binding of Acetylcholine Na+ channel

Inward Na+ current causes polarisation - which in turn causes a response

How is GABA receptor an ionotropic receptor ?

GABA - signal molecule - neurotransmitter

GABA binds to ion channel - causes influx of Cl- ions - inhibitory receptors - causes relaxation

What are metabotropic Aka muscarinic receptors ?

Receptors that produce molecules that act as precursors for the signal molecule for the ion channel receptor

Provide indirect link with ion channels through signal transduction pathways

Differences between Ionotropic and metabotropic receptors.

Ionotropic - direct response by ion channel pore

Metabotropic - indirect - slower - mediated by G proteins - transducers

What are G protein coupled receptors ?

Receptors that transduce a signal by forming a receptor-g protein complex which in turn activates an enzyme to produce a response.

Structure of G proteins

7 transmembrane domains

3 polypeptide chains - alpha, beta and gamma

16 alpha subunits, 5 beta, 11 gamma

All beta and gamma subunits bind tightly to each other to form one beta-gamma unit

Alpha subunit has a guanine nucleotide binding site that binds GTP or GDP

Explain the G protein cycle

What is the cAMP/PKA pathway ?

Important mechanism that allows hormones /neurotransmitters to evoke response in target cells

Present in virtually every cell

Uses proteins that get phosporylated by PKA to transduce a signal