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CELL SIGNALLING

Explore how cells communicate with each other and the outside world through cell signalling mechanisms, including neurotransmitters, hormones, and transduction processes in unicellular and multicellular organisms.

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CELL SIGNALLING

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  1. 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.

  2. COMMUNICATION • Transmitter • Receiver Transduction Mechanism

  3. 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

  4. Oxytocin = Swift Birth 7.1.2. Signalling Molecules

  5. 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

  6. 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

  7. 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

  8. 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

  9. The Neuromuscular Junction

  10. G Protein

  11. 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.

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

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

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