Receptors and Signalling Flashcards
(30 cards)
What is a ligand?
Any molecule that binds to a receptor
May be an agonist or antagonist
What are endogenous agonists?
Chemical mediators that are found naturally in the body that bind to a receptor producing a response
e.g. ACh, noradrenaline, insulin
What are nonendogenous agonists?
Drugs
What is convergent signalling?
Single cells can integrate information and create a single response
- All cells express multiple types of receptors
What is amplification of signalling?
Different types of receptors may use similar transduction mechanisms
What is divergent signalling?
Allows coordinated responses involving multiple organs
- Most EC signal molecules can act on more than one type of cell
What are receptors?
Macromolecular proteins that serve as recognition sites for chemicals and used in cell-cell communication
Also any protein of a cell that can bind a molecule, to modulate an activity of the cell
How are receptors classified?
- Receptors within a class share common overall features
- There are three classes on cell surface each with:
- Transmembrane-spanning segments
- Ligand-binding domain (extracellular)
What are the 4 receptor types?
Type 1 - Ligand-gated ion channels (ionotropic receptors)
Type 2 - G protein coupled receptors (metabotropic) - can influence metabolic cascade within cell
Type 3 - Kinase-linked receptors e.g. insulin receptors
Type 4 - Nuclear receptors (no transmembrane proteins)
What are nuclear receptors?
- Polypeptides with multiple domains
- Ligands hydrophobic so can cross membrane
- Act as transcription factors - binding to DNA and regulating gene expression
e.g. steroid hormone receptors
What receptor types do small molecule chemical mediators use?
Type 1 and 2
What receptor types do peptide hormones use?
Type 2 and 3
What receptor types do steroidal hormones use?
Type 4
How are signals transduced?
1) Ligand binding
2) Conformational change in receptor
3) Generation of intracellular signal or second messenger
What does transduction mechanism and type of IC signal influence?
Type, speed, duration of response
When do ligand-gated ion channels open?
On agonist binding
Involved in fast synaptic transmission
The endogenous agonists are fast/classical NTs stored in synaptic vesicles e.g. ACh, Glutamate, GABA
How are ligand-gated ion channels structured?
- Composed of 3-5 subunits (i.e. transmembrane proteins)
- Complex arrangement to form central aqueous pore , usually ligand binding domain on outisde
When do ligand-gated ion channels close?
When agonist is removed or receptor enter ‘desensitised state’ - takes time for it to be ready to open again
What are nAChRs?
Nicotinic acetylcholine receptors
- An excitatory ligand gated ion channel
- Pentameric and heteromeric - 5 different subunits make up channel
Where are nAChRs found?
Neuromuscular junctions
Autonomic nervous system
Some parts of brain
What are the agonists of nAChRs?
Endogenous - ACh
Non-endogenous - Nicotine
What does opening nAChRs cause?
Results in excitation
1) Excitatory NTs (ACh) bind to nAChR activating them
2) Ions (Na+) flow through open channels
3) Changes the potential of the cell - membrane depolarisation
How is inhibition caused via LG ion channels?
GABA activates GABA(A) receptors which allow Cl- through
Causes membrane hyperpolarisation
What is the structure of G protein coupled receptors?
Single transmembrane protein
7 transmembrane domains
EC binding domain on outside
G protein binding domain on inside
