L4 Receptors and signalling Flashcards
What are ligands?
Ligands are any molecules that bind to a receptor whether they are an agonist or an antagonist.
What are endogenous agonists? Eg?
They are chemical mediators that are found within the body that bind to receptors to stimulate a response .Eg. Acetylcholine, noradrenaline and insulin.
What does chemical mediators do in cell signalling?
Chemical mediators are extracellular signal molecules that bind to specific receptors on target cells to initiate intracellular signals that alter cell behaviour through effector proteins, this is called cell signalling.
What is Signal transduction?
The process of converting extracellular signal to an intracellular signal or a second messenger is called signal transduction.
What are the general principles of chemical communication and cell signalling?
Convergence and divergence
What does convergence principle mean?
All the cells express multiple types of receptors with single cells integrating information and different types of receptors may use similar
signal transduction methods which allows amplification of signalling.
What does divergence mean?
Most of the extracellular signal molecules act on more than one cell type that is which leads to the response of the same receptor expressed by more than one cell type which allows coordinated response involving multiple organs.
What does receptors respond to and how?
Receptors recognise and respond specifically to signal molecules. Receptors are macromolecules that provides recognition sites for neurotransmitters, hormones and chemicals used in cell-cell communication.
Receptors also refer to any protein of a cell that can bind a molecule which then modulates some kind of activity. 1000s of receptors are there and knowledge of function allows prediction of physiology.
How are receptors classified and what are they?
Receptors are classified by their structure into 4 classes or superfamilies.
They are:
1. Type 1 - Ligand gated ion channels (ionotropic receptors)
2. Type 2 - G protein coupled receptors( metabotropic receptors)
3. Type 3 - Kinase linked receptors.
4. Nuclear - Intracellular receptors.
What are the physiological features present in the first three classes of receptors?
Each has transmembrane-spanning segments, they possess a ligand binding domain usually extracellular, and ligands are hydrophilic meaning they cannot cross the membrane.
What are the adaptations present in nuclear receptors? Eg ?
They contain polypeptides with multiple domains, ligands are hydrophobic, acts as transcription factors binding to DNA and regulating gene transcription .Eg. Steroid hormone receptors including oestrogen receptors.
Which chemical mediators use which receptor types?
- Most of the small molecule chemical mediators such as amino acid derived neurotransmitters use ligand gated ion channels and g protein receptors,
- Peptide hormones use G protein coupled receptors (Muscarinic ACh receptor) and kinase linked receptors.
- Cytokines use kinase-linked receptors.
- Steroidal Hormones use Nuclear receptors.
What is the time scale effects for Ligand-gated ion chanells, G protein coupled receptors, kinase - linked receptors and nuclear receptors?
Time Scale:
1. Ligand Gated ion channels - Milliseconds
2. G Protein-coupled receptors - Seconds
3. Kinase - linked receptors - Hours
4. Nuclear receptors - Hours.
What is the order of function in an intracellular signal?
- Ligand binding
- Confrontational change in the receptor
- Generation of an intracellular signal.
What are the cellular effects of Receptor activation?
- Electrical signals( Ligand gated ion receptor) Eg: triggering action potentials
- Contractility and muscle movements (G protein coupled receptors).
- Changes in enzyme activity (Kinase - linked receptors).
4.More channels to be inserted into the cell membrane. (Nuclear receptors).
