CELL SIGNALLINGCELL 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.

COMMUNICATIONCOMMUNICATION

Transmitter

Receiver

Transduction Mechanism

CELL - CELL SIGNALLINGCELL - 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

7.1.2. Signalling Molecules7.1.2. Signalling Molecules

Oxytocin = Swift Birth

Signalling MoleculesSignalling 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

TRANSDUCTIONTRANSDUCTION

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 Extracellular Hydrophobic Signalling (steroids) 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 Extracellular Hydrophilic SignallingSignalling

Signal molecule binds to a receptor protein on cell membrane’s surface

3 possible outcomesIon 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 JunctionThe Neuromuscular Junction

G ProteinG Protein

G-Protein Linked ReceptorsG-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 cascadeActivation cascade

Adrenaline stimulates liver cells to breakdown glycogen

Acts via G protein/ cAMP cascade

Coffee/ TeaCoffee/ Tea

Caffeine potentiates the action of cAMP by inhibiting its breakdown by phosphodiesterase