Cell Signaling Flashcards
Why do cells need to communicate?
Process information
Self preservation
Voluntary movement
Homeostasis
What are the 4 types of signalling?
Endocrine
Paracrine
Membrane attached proteins
Autocrine
What is endocrine communication?
Hormone travels within blood vessels to act on a distant target cell
Example of endocrine communication.
Hypoglycaemia
- glucagon secreted by alpha cells of Islets of Langerhans
- travels out of pancreas in blood vessels
- stimulates glycogenolysis and gluconeogenisis w/in liver
—> increasing blood glucose levels
What is paracrine communication?
Hormone acts on adjacent cell
Example of paracrine communication.
Hyperglycaemia
- increased blood glucose - insulin secreted by beta-cells in Islets of Langerhans
- insulin has paracrine effects —> inhibiting glucagon secretion
- also has endocrine effects on the liver
What is membrane attached protein signalling?
Plasma membrane proteins on adjacent cells interacting
Example of membrane attached protein signalling
Blood borne virus —> detected in blood by antigen presenting cell
APC digests pathogen —> express major histo-compatibility class II molecules on surface
Circulating T-lymphocyte engages with MHC molecule through T-cell receptor interaction
What is autocrine communication?
Signalling molecule acts on the same cell
Example of autocrine signalling
Activates TCR will initiate a cascade o reaction within T-cell
Activated T-cell expresses interleukin-2 receptor on surface
Activated T-lymphocyte also secretes IL-2 which:
—> binds to IL-2 receptor on the same cell
—> binds to IL-2 receptor on adjacent activated T-cell
Process of neurotransmission.
- Propagation of the action potential
- Neurotransmitter release from vesicle
- Activation of postsynaptic receptors
- Activation of postsynaptic receptors
What are the 4 types of receptors?
Ionotropic
G-protein coupled
Enzyme-linked
Intracellular
What is an ionotropic receptor
Ligand binding —> opens ion permeable pore traversing the membrane
Events in an ionotropic receptor.
Ligand binds to the receptor protein
Change in conformation of channel protein —> opens pore
Pore allow soins to move in our out of cell
Ionotropic receptor example
Nicotinic Acetylcholine
Ligand: ACh
Location: skeletal muscle
Physiological effect: muscle contraction
What is a G-protein coupled receptor?
Ligand binding —> activates intracellular G-protein
Events in a G-protein coupled receptor
7-TM receptor & heterotrimeric G-protein are inactive
Ligand binding —> changes conformation of receptor
Unassociated G-protein binds to the receptor —> GDP is exchanged for GTP
G-protein dissociates into two active components:
—> alpha - subunit
—> beta gamma - subunit
bind to their target proteins
Internal GTPase activity on alpha - subunit dephosphorylates GTP —> GDP
Alpha - subunit dissociates from target protein —> inactive again
Receptor remains active as long as ligand is bound and can activate further heterotrimeric G-proteins
G-protein coupled receptor example
Gs protein linked receptor
—> stimulates adenylyl cyclase
—> beta-adrenergic receptor
Gi protein linked receptor
—> inhibits adenylyl cyclase
—> M2-muscarinic receptor
Gq protein linked receptor
—> stimulates phospholipase C
—> AT-1 angiotensin receptor
What is an enzyme linked receptor?
Ligand binding —> receptor clustering —> activates internal enzymes
Events of an enzyme-linked receptor
Ligand binding
Receptor clustering activates enzyme activity w/in cytoplasmic domain
Enzymes phosphorylate receptor
Phosphorylation —> binding of signalling proteins to cytoplasmic domain
These signalling proteins —> recruit other signalling proteins —> signal generated in cell
Examples of enzyme-linked receptor
Insulin receptor
What is an intracellular receptor?
Membrane permeable ligand binds to receptor inside cell
Events in an intracellular receptor
Type 1 - Cytoplasmic
Located within the cytosolic compartment
Associated with chaperone molecules (heat
shock proteins, hsp)
Hormone binds to receptor ® hsp dissociates
2 hormone bound receptors form a
homodimer.
The homodimer translocates to the nucleus —> binds to DNA
Type 2 - Nuclear
Located within the nucleus
Binding of hormone ligand —> transcriptional regulation
Example of intracellular receptors
Type 1: glucocorticoid receptor
Ligand: cortisol, corticosterone
Physiological effect: lower immune response, more gluconeogenisis
Type 2: thyroid hormone receptor
Ligand: thyroxine (T4), triiodothyronine (T3)
Physiological effect: growth and development
