Cell Signalling Flashcards
Outline the communication which takes place during hypoglycaemia. What type of communication is it?
Endocrine communication takes place, as the alpha cells of Islets of Langerhans in the pancreas secrete glucagon, which travels out of the pancreases through blood vessels to stimulate gluconeogenesis and glycolysis in the liver, to increase glucose levels in the blood.
What is paracrine communication?
Intercellular communication, hormone acts on an adjacent cell.
Give three examples of paracrine communication
NO produced by endothelial cells in blood vessels, osteoclast activating factors, produced by adjacent osteoblasts for bone regeneration and insulin secretion by beta cells in the islets of langerhans to inhibit the glucagon secretion of alpha cells.
What is autocrine communication?Give an example
Molecular signalling occurring within the same cell. Example is when an activated TCr expresses interleukin-2 (IL-2) receptor on surface membrane, which binds to IL-2, rebased by the same TCR, or can act on adjacent cells.
Describe the process of action potential propagation
Voltage gated Na+ channels open, causing an influx of Na+, membrane depolarisation and action potential to move along the axon, voltage gated K+ channels to open and repolarisation.
How do ionotropic receptors work? Give examples
A stimulant, like a hormone or an ion, binds to the receptor, changing the protein’s confirmation of the receptor, and opening a pore in the membrane. The pore allows ions to move in/out of the cell, according to conc. gradient. Examples include Nicotinic acetylcholine receptor, GABA and glutamate/NMDA
How do G-protein coupled receptors work?
7-TM receptor anf G-protein receptor and inactive, and then ligand binding change their conformation, making them active. They will remain active as long as the ligand is bound to it. The G-protein now binds to the active 7-TM, and becomes activated via the phosphorylation of GDP into GTP (or exchanged), which causes the G-protein to break down into an alpha and a gamma subunits, which can act on the target protein/molecule, after which the GTP is phosphorylated, the G-protein decouples and becomes inactive.
How do Gs receptors work? Examples?
Work by stimulating adenylyl cyclase, which catalyses the conversion of ATP into cAMP, which then activates protein kinase A (PKA). Examples include the B-adrenergic receptor, located in heart)
How do Gi receptors work? Examples?
Inhibit adenyl cyclase, reducing PKA levels. Examples include M2-muscarinic receipts in heart, which lowers heart rate.
How do Gq receptors work? Examples?
They stimulate phospholipase C (PLC), which catalyses PIP2 conversion into IP3(this stimulates Ca2+ release, causing cellular contraction), which then reacts with DAG, which then activate PKC. An example of this is an A-1 angiotensin receptor in blood vessels, which causes vasoconstriction.
How do enzyme-linked receptors work?
A ligand binding causes the receptor to cluster, activating an enzyme in the cytoplasmic domain. The enzyme then phosphorylates the receptor. This phosphorylation causes the binding of signalling proteins tot the cytoplasmic domain. These signalling proteins can then recruit other signalling proteins, and a signal is generated within the cell.
How do type 1 intracellular receptors work? Where are they located? Example?
These are found in the cytosol, and are associated with heat-shock proteins. They work when a hormone binds to them, causing the HSP to dissociate. Two of the hormone bound receptors for a dimer (homodimer), which translocates to the nucleus and binds to DNA. An example is the glucocorticoid receptor, which reduces immune response and increases gluconeogenesis.
How do type 2 intracellular receptors work? Where are they located? Example?
These are found within the nucleus. The binding of the hormone ligand will cause a transcriptional regulation to take place. An example of this is the thyroid hormone receptor, involved in growth and development.
