CELL SIGNALLING Unicellular organisms Awareness of environment –Nutrients, light etc. Multicellular organisms Coordinating whole body responses Regulating specialist functions of tissues Cells need to communicate with the outside world and with each other.

COMMUNICATION Transmitter Receiver Transduction Mechanism

CELL - CELL SIGNALLING 4 Types – Endocrine Hormone secreted into bloodstream Signalling/ target cells far apart Slow (10s of seconds) – Paracrine Local release of chemical into interstitial fluid (fluid surrounding cells) Local action – Neuronal Neurotransmitter released by nerve at synapse Long distances Very rapid (mseconds) – Contact dependent signalling Restricted to directly joined cells

Signalling Molecules Oxytocin = Swift Birth

Signalling Molecules Proteins e.g. Somatotropin (hGH), oxytocin (partuition, suckling, love), vasopressin (love/ memory) Amino Acids e.g. GABA (  amino butyric acid) reduces nerve activity (valium stimulates GABA action) Serotonin (5HT) Ecstasy damages these nerves Glutamic acid Memory & Learning, Nerve damage during stroke/ head injury Gases Nitric oxide (NO) - stimulates vasodilation Viagra enhances production of NO Steroid Hormones Testosterone/ oestrogen

TRANSDUCTION Hydrophilic transmitters e.g. Proteins/ amino acids – Can’t pass across lipid membrane – Bind to membrane receptors (proteins) Hydrophobic transmitters e.g. Steroid hormones, thyroid hormones, nitric oxide (small – Can pass directly through membrane – Bind to cytosolic receptors

Extracellular Hydrophobic Signalling (steroids) Signal molecule dissolves into cell membrane – Diffuses across membrane Binds to a cytosolic receptor protein – Receptor/steroid complex transported into nucleus – Influences gene transcription

Extracellular Hydrophilic Signalling Signal molecule binds to a receptor protein on cell membrane’s surface 3 possible outcomes Ion channel opened (e.g Acetylcholine ) –Produces a change in polarity of cell Receptor linked to a GTP binding protein (G-protein) e.g. adrenaline –Activates the G-protein –Signal stimulates a variety of cellular events Receptor part of an enzyme, binding activates enzyme e.g. insulin receptor is a tyrosine kinase –Usually kinase/ phosphatase –Phosphorylates/ dephosphorylates proteins

The Neuromuscular Junction

G Protein

G-Protein Linked Receptors Transmitter binds to receptor. Conformational change of receptor protein – G Protein binds to receptor protein on intracellular surface – Conformational change in G – protein, causing it to bind GTP. – G protein (with GTP bound) migrates in membrane – Binds to and activates adenyl cyclase enzyme (ATP  cAMP) cAMP second messenger activates variety of targets. cAMP broken down by phosphodiesterase – switches activation off. The G protein remains active whilst GTP is bound – G protein hydrolyses GTP  GDP and thus becomes inactive.

Activation cascade Adrenaline stimulates liver cells to breakdown glycogen Acts via G protein/ cAMP cascade

Coffee/ Tea Caffeine potentiates the action of cAMP by inhibiting its breakdown by phosphodiesterase