Transcript CELL SIGNALLING

CELL SIGNALLING
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Unicellular organisms
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Awareness of environment
– Nutrients, light etc.
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Multicellular organisms
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Coordinating whole body responses
Regulating specialist functions of tissues
Cells need to communicate with the outside
world and with each other.
COMMUNICATION
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Transmitter
Transduction
Mechanism
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Receiver
CELL - CELL SIGNALLING
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4 Types
– Endocrine
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Hormone secreted into bloodstream
Signalling/ target cells far apart
Slow (10s of seconds)
– Paracrine
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Local release of chemical into interstitial fluid (fluid
surrounding cells)
Local action
– Neuronal
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Neurotransmitter released by nerve at synapse
Long distances
Very rapid (mseconds)
– Contact dependent signalling
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Restricted to directly joined cells
7.1.2. Signalling Molecules
Oxytocin = Swift Birth
Signalling Molecules
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Proteins e.g.
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Somatotropin (hGH), oxytocin (partuition, suckling, love), vasopressin
(love/ memory)
Amino Acids e.g.
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GABA ( amino butyric acid) reduces nerve activity
• (valium stimulates GABA action)
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Serotonin (5HT)
• Ecstasy damages these nerves
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Glutamic acid
• Memory & Learning, Nerve damage during stroke/ head injury
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Gases
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Nitric oxide (NO) - stimulates vasodilation
• Viagra enhances production of NO
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Steroid Hormones
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Testosterone/ oestrogen
TRANSDUCTION
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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)
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Signal molecule dissolves into cell
membrane
– Diffuses across membrane
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Binds to a cytosolic receptor protein
– Receptor/steroid complex transported into
nucleus
– Influences gene transcription
Extracellular Hydrophilic
Signalling
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Signal molecule binds to a receptor protein
on cell membrane’s surface
 3 possible outcomes
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Ion channel opened (e.g Acetylcholine )
–Produces a change in polarity of cell
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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
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–Usually kinase/ phosphatase
–Phosphorylates/ dephosphorylates proteins
The Neuromuscular Junction
G Protein
G-Protein Linked Receptors
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Transmitter binds to receptor.
 Conformational change of receptor protein
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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)
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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
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Caffeine potentiates the action of cAMP by
inhibiting its breakdown by
phosphodiesterase