CELL%20SIGNALLING

1
(No Transcript)
2
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.

3
COMMUNICATION

• Transmitter
• Receiver

Transduction Mechanism
4
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

5
7.1.2. Signalling Molecules
6
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

7
TRANSDUCTION

• Hydrophilic transmitters e.g. Proteins/ amino
  acids
• Cant 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

8
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

9
Extracellular Hydrophilic Signalling

• Signal molecule binds to a receptor protein on
  cell membranes 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

10
The Neuromuscular Junction
11
G Protein
12
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.

13
Activation cascade

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

14
Coffee/ Tea

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

15
(No Transcript)