basic principles of communication

general principles of signalling to target cells

• need signalling molecules/ligands/transmitters/endogenous antagonists

• target cells respond by specific receptor proteins

• some receptors intracellular

local signalling

• contact dependent- membrane bound signal

• paracrine- release paracrine factors

• autocrine- where the signalling cell is the target cell

• includes unicellular and multicellular

distant signalling

• endocrine

• synaptic

• increased size and complexity of animals requires both long distance and local signalling

common mechanisms of cell signalling

• neurotransmitters

• hormones

• ligand gated ion channel

• G protein coupled receptors

• receptor tyrosine kinases

• transcription factors

common cellular responses

• depolarisation

• depolarisation and electro mechanic coupling (muscle)

• depolarisation and secretion (endocrine glands)

• transcriptional and translational effects (all cells)

general structure of plasma membrane receptor

• 3 domains or origins

• N terminus on extracellular domain

• C terminus on intracellular domain

• eg G coupled

3 types of cell surface receptors

• ion channel linked

• enzyme linked

• G protein coupled receptors

g protein linked receptors

• what are they

• what relays the signal

• what leads to the genration of second messenger

• what are the 3 subunits and how many types of each are there

• family of 7 pass transmembrane proteins

• trimeric g proteins relay signal

• coupling receptor to its target generating second messengers eg cAMP, IP3, DAG

• alpha subunit used to define G protein (at least 20 diff subtypes)

• at least 5 types of beta subunit

• at least 10 types of gamma subunit

• different combinations of subunits define the function

stimulatory g proteins

• how do they signal

• how is this signalling molecule generated

• what is activated and how does this affect cells

• signal via secondary messengers cAMP

• free active stimulatory g protein interact with adenyl cyclase at membrane generating cAMP from ATP so cAMP conc rapidly rises

• cAMP activates serine threonine protein kinase, which phosphorylates protein substrates to affect cells

how do transmitters achieve specificity

activating target cells which express the cognate receptor

what does the duration of the signal depend on?

the half life of the transmitter

gcpr- fight or flight

• A1 receptors- linked to gq, which generates IP3 and DAG- expressed on smooth muscles on some arterioles leading to muscle contraction

• B receptors- linked to gs which generates cAMP, expressed on

  • cardiac muscle

  • smooth muscle of bronchi

  • smooth muscle of other arterioles