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Flashcards in 9. Signalling between cells II Deck (23)
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Describe Ionotropic receptor signal transduction events

1. Ligand binds to the receptor protein
2. Change in conformation of channel protein: opens pore
3. Pore allows ions to move in or out of cell according to their respective concentration gradients


Give 2 examples of ionotropic receptors.

Nicotinic Acetylcholine Receptor
GABAA Receptor


Describe the Nicotinic Acetylcholine Receptor

Ligand: Acetylcholine (ACh)
Location: Skeletal muscle
Physiological effect: Muscle contraction


Describe the GABAA receptor

Ligand: gamma-amino butyric acid (GABA)
Location: Neuronal
Physiological effect: decrease neuronal excitability


Describe the activation process of a G-protein coupled receptor

Ligand binds and changes conformation of the receptor
Unassocciated G protein binds to the intracellular part of receptor (it has a GDP bound to it)
GDP is exchanged for GTP
GTP allows the dissociation of the alpha subunit and the beta-gamma subunit of the G protein
Subunits bind to target proteins
Once the alpha subunit has fulfilled its function, GTPase activity on dephosphorylates GTP to GDP
Allows alpha subunit to dissociate from target protein and reform the heterotrimer with GDP attached


What is a G-protein coupled receptor?

Heterotrimeric of alpha, beta and gamma chains with a GDP attached


What are the 3 types of G alpha subunits?

G alpha S
G alpha I
G alpha Q


What is the function of G alpha S?

Stimulates adenyl cyclase
Converts ATP to cAMP
cAMP activates PKA


Give an example of action of G alpha S

Beta-1- adrenergic receptor in sympathetic nervous system
Increases heart rate and force of contraction


What is the function of G alpha I?

Inhibits adenylyl cyclase
Thus, reduces levels of PKA


Give an example of action of G alpha I

M-2- muscarinic receptor in parasympathetic nervous system
Decreases heart rate


What is the function of G alpha Q?

Stimulates phospholipase C (PLC)
Converts PIP2 to IP3 and DAG
IP3 stimulates Ca2+ release
DAG activates PKC
Important in smooth muscle contraction and vasoconstriction


Give an example of action of G alpha Q

AT-1 angiotensin receptor
Causes vasoconstriction


Describe the action of enzyme-linked receptors.

Ligand binds to the receptors, causes receptor clustering
Clustering of receptors activates intracellular enzymes,
Enzymes phosphorylate receptor which leads to binding of signalling proteins to cytoplasmic domain
Signalling proteins recruit other signalling proteins, generate a signal


What are the 3 types of enzyme-linked receptor?

Tyrosine Kinase (95%)
Serine-Threonine Kinase


Describe the insulin receptor (CD220 antigen)

Ligand: Insulin
Physiological effect: Glucose uptake


Describe the ErbB receptor

Ligand: Epidermal Growth Factor, Transforming Growth Factor beta
Physiological effect: Cell growth, proliferation


Describe a guanylyl-cyclase linked receptor

Ligand: Atrial/ Brain natriuretic peptide
Physiological effects: Vasodilation, decreases BP
=diagnostic marker


Describe a Sea/Thr-kinase linked receptor

Ligand: Transforming growth factor beta
Physiological effect: Apoptosis


Describe the action of Type 1 Intracellular Receptors

Located in cytosolic compartment, bound to heatshock proteins (chaperone molecules)
Ligands (usually steroids as permeable) pass through the membrane and bind to the receptor, causes dissociation from heatshock protein
2 hormone bound receptors form a homodimer
Homodimer translocates to the nucleus and bind to the DNA
Causes increased/ decreased transcription (slow)


Describe the action of Type 2 Intracellular Receptors

Located in nucleus, already bound to DNA
Ligand passes through the membrane and through the nuclear envelope
Binds to the receptor causing changes in transcription


Give an example of a Type 1 Intracellular Receptor.
State its ligands and physiological effects

Glucocorticoid receptor
Ligands: Cortisol, corticosterone
Physiological effect:
Downregulates Immune response
Increases Gluconeogenesis


Give an example of a Type 2 Intracellular Receptor. State its ligands and physiological effects.

Thyroid hormone receptor
Ligand: Thyroxine (T4), triiodothyronine (T3)
Physiological effect: Growth and development