Week 2 Cell Signalling – direct & indirect I Flashcards
Why do cells signal?
- division
- growth
- differentiation
- motility
- metabolism
- death
- secretion
- absorption
To ingegrate the above, communication is key!
How do cells signal (direct vs. indirect)?
Cell-cell communication via chemical messengers (signalling molecules):
-
Direct signalling
- Gap junctions
- Juxtacrine signalling (adjacent)
-
Indirect signalling
- Autocrinesignalling (“self”)
- Paracrinesignalling (neighbouring)
- Endocrinesignalling (at a distance)
- Neuronalsignalling (at a distance)
What types of cells are involved in cell signalling?
- Hormones
- e.g. adrenaline [epinephrine], insulin, testosterone
- Growth factors
- e.g. insulin-like growth factors
- Inflammatory molecules
- e.g. cytokines, prostaglandins
- Neurotransmitters
- e.g. acetylcholine, dopamine, GABA, noradrenaline [norepinephrine]
How are signals received?
Receptors – proteins that bind the signal molecule to induce a conformational change
How are signals received: What are secondary messengers?
What are the types of receptors?
- Ion channels
- e.g. nicotinic acetylcholine receptor
- G-protein-coupled receptors (GPCR)
- e.g. adrenoceptors, glucagon receptor
- Enzymatic receptors
- e.g. insulin and growth factor receptors
- Nuclear receptors
- e.g. thyroxine, vitamin D and steroid hormone receptors
What is Gap junction signalling? How does it work?
- Ions and small molecules exchanged between cells via gap junctions
- Each adjacent cell has hemichannels (molecular hexamer) in plasma membrane
-
Hemichannels formed of either hexameric:
- connexins (vertebrates) – form connexon
- innexins (invertebrates) – form innexon
- Each connexin or innexin monomer has 4 transmembrane α-helixes (i.e. each hemichannel has 24 transmembrane domains)
What is Juxtacrine signalling? How does it work?
- Ligand in plasma membrane of signalling cell A (e.g. ephrin)
- Receptor in plasma membrane of adjacent target cell B (e.g. eph receptor)
- Important for cell migration
What is indirect signalling? How does it work?
- Signalling cell produces a chemical messenger / signalling molecule
- In most cases, signalling molecule secreted into ECF / lymph / blood
- S Molecule transported over distance (short, medium or long) to target cell
- S Molecule acts as ligand for receptor on / in target cell
- S Molecule elicits cellular response in target cell
What is autocrine signalling? How does it work?
- Cell produces a local ligand that acts back on the receptor in the same cell
- Allows cell to sense extracellular environment (biochemical radar)
What is paracrine signalling? How does it work?
- Cell produces a local ligand that acts on neighbouring cells
- Moves over short distances by diffusion (e.g. local recruitment of inflammatory cells by mast cells via histamine)
What is endocrine signalling? How does it work?
- Cell-cell communication over long distances
- Signalling cell termed an endocrine cell
- Signalling molecules (hormones) transported in circulatory system – blood (or lymph)
What is neural signalling? How does it work?
- Messages (nerve impulses) travel long distances but chemical messengers only travel short distances:
- Long distances – action potentials
- Synaptic transmission – signalling molecules
What is neuroendocrine signalling? How does it work?
Posterior pituitary nonapeptide hormones:
- Oxytocin (OT)
- (Arginine) Vasopressin (AVP)
What is the speed of communication for the different types of cell signalling?
- Autocrine – shortest distance – msec to sec
- Paracrine – short distance – msec to sec
- Endocrine – long distance – sec to mins
(can be hours to days!)
• Neural – long distance – msec only!
What is the classification of signalling molecules?
6 major classes of signalling molecules:
How are peptide secreted?
Exocytosis: a secretory vesicle fuses with the plasma membrane, releasing the vesicale contents to the cell exterior. The vesicale membrane becomes part of the plama membrane.
