Tissues 9 Flashcards
How do Ionotropic receptors work?
- Ligand binds to receptor protein
- Channel protein changes conformation - opens pore
- Allows ions to move freely - depending on concentration gradients.
Give 2 examples of ionotropic receptors.
- Nicotinic Acetylcholine receptors.
2. GABA receptors
What physiological effect does GABA have?
Depression of activity (influx of Cl).
Blocking GABA receptors gives hyperexcitability of CNS
Explain how G-protein coupled receptors work.
- “G protein” initially not linked to the G-protein receptor (receptor aka known as 7-TM receptor)
- Ligand binds to receptor and changes its conformation
- Stimulates G-protein to bind to associate with G-protein receptor
- GDP exchanged for GTP.
- G-protein dissociates into 2 active components.
- Alpha subunit
- By subunit
- Each subunit binds to its target protein.
- Once alpha subunit binds to target protein, internal GTP-ase activity causes GTP to change to GDP.
- Alpha subunit unbinds from target protein. Heterotrimer with GDP reforms.
G proteins are called heterotrimers. What is the meaning of this.
Alpha, beta and gamma subunits.
Beta and Gamma don’t dissociate in G protein
G(s) Protein Linked Receptor. What does it do.
- Stimulates Adenylyl Cyclase.
- Adenyl cyclase converts ATP to cAMP.
- cAMP increases Protein Kinase A (PKA) levels
Give an example of Gs Protein linked receptor
Beta1-adrenergic receptor
beta-blockers act on this receptor
G(i) Protein Linked Receptor. What does it do.
- Inhibits Adenyl cyclase.
2. Reduces levels of cAMP and PKA.
Give an example of Gi protein linked receptor.
M2 - Muscarinic receptor
What does the G(q) protein linked receptor do?
- Stimulates Phospholipase C (PLC)
- PLC converts PIP2 to IP3 and DAG
- IP3 causes an increase in intracellular Ca
- DAG activates PKC
What are G(s), G(i) and G(q)?
All types of G(a) subunits.
What is the effect of the G(q) receptor?
Works on the AT-1 angiotensin receptor. Effect is vasoconstrictor
What is the most potent vasoconstrictor in the body?
Angiotensin
Explain how enzyme linked receptors work.
- Ligand binding causes receptors to cluster.
- Receptor clustering activates enzymes within cytoplasm.
- Enzymes phosphorylate receptor.
- Phosphorylation causes signalling proteins to bind to the cytoplasmic domain.
- Signalling proteins recruit other signalling proteins and signal generated.
What are the majority of enzyme linked receptors related to?
Tyrosine Kinase Enzymes
What does tyrosine kinase do?
Phosphorylate any protein with an a tyrosine amino acid in it
How is the signal from an enzyme linked receptor terminated?
When a phosphatase removes the phosphate group
Give examples of Tyrosine Kinase enzyme linked receptors.
- Insulin receptor (CD 220)
2. ErbB receptor (ligand is Epidermal growth factor, Transforming Growth Factor Beta)
What are the 3 types of enzyme linked receptor?
- Tyrosine Kinase Linked Receptor (95%)
- Guanylyl-cyclase Linked receptor
- Serine-Threonine Kinase Linked Receptor
How does a cytoplasmic intracellular receptor (Type 1) work?
- Located in cytosol, attached to Heat Shock Proteins
- Hormone (usually steroids) bind to receptor.
- Causes HSP to detach
- Two hormone bound receptors form a HOMODIMER
- Homodimer translocates to nucleus. Binds to DNA.
How does a nuclear intracellular (Type 2) receptor work?
- Located within nucleus.
- Hormone ligand binds.
- Causes transcriptional regulation.
Intracellular receptors are actually transcription factors. They usually take shorter/longer for effects to occur?
Longer
Give an example of an intracellular cytoplasmic (Type 1) receptor.
Glucocorticoid Receptor
Ligand - cortisol, coricosterone
Physiological Effects - Downregulates immune response, increases gluconeogenesis
Give an example of a nuclear intracellular (Type 2) receptor.
Thyroid Hormone Receptor.
Ligand - Thyroxine (T4), Triiodothyronine (T3)
Physiological Effects - Growth and Development
