Signal Transduction 2: G Protein-coupled Receptor Signal Transduction Flashcards
What are the three main types of transmembrane receptors?
- G-protein coupled receptors (GPCRS)
- Receptor tyrosine kinase (RTKs)
- Ligand-gated ion channel receptors
What are G protein coupled receptors?
Receptors that work with the help of a G protein (and second messengers)
What is receptor tyrosine kinase?
Receptors that attach phosphates to tyrosines to signal (phosphorylation cascades etc)
What are ligand-gated ion channel receptors?
A signal molecule binds as slogans to the receptor, opening the receptor gate, allowing specific ions (eg Na or Ca) to pass through a channel in the receptor in the cell
Ligand signals
What are intracellular receptors?
Found in the cytoplasm or nucleus of target cells and are for small or hydrophobic chemical messengers that can readily cross the membrane to activate them (e.g steroid and thyroid hormones of animals- there are fewer of these receptors)
What sort of receptor could epinephrine bind to on a GPCR?
B-adrenergic receptor
Whet sort of things can bind to a g-protein?
A lot; light, Ca, small microbes: amino acids, fatty acids, nucleotides, amines, prostaglandins, peptide, proteins (TSH, LH, FSH, chemokines)
When are GPCRS active?
At the cell surface where their hormone can access them
What are the key structural features of a G-protein?
7 transmembrane regions (serpentine)
Extra cellular N-terminus
Intracellular C-terminus
What does transmitting messages across a cell membrane involve for the GPCR receptor?
A conformational change (as the receptor is a gate-keeper of cellular activity, control hormone activity at the cell surface)
Describe the heterotrimeric G protein?
Has an a-subunit and a B-y dimer
What do G proteins bind to?
Guanine nucleotides
What is a G protein?
A guanine nucleotide binding protein
What is GDP?
Guanosine diphosphate
What is GTP?
Guanasine triphosphate
What binds to the effector in the G protein cycle?
Alpha GTP which binds to adenylate cyclase to produce cAMP from ATP (aGTP converted to aGDP)
What is cyclic adenosine Monophosphate?
A first second messenger which is a common mediator for many hormones
What makes cyclic adenosine Monophosphate?
Enzyme adenylate cyclase
What does cyclic AMP do?
Converts inactive protein kinase a to active protein kinase A
What does active protein kinase a do?
Converts inactive phosphorylase kinase to active phosphorylase kinase
What does active phosphorylase kinase do?
Converts inactive glycogen phosphorylase to active glycogen phosphorylase
What are the three different classes of G protein?
Gs (stimulatory G protein that activates adenylate cyclase)
Gi (inhibitory G protein, inactivates adenylate cyclase)
Gq (activates a different effector, phospholipase C)
What do Gs favour?
Catalytically active form of adenylate cyclase (increases cAMP)
What do Gis favour?
More catalytically inactive form of adenylate cyclase (decreases cAMP)
What do Gs and Gi allow for?
Opposing biological effects
What do Gi and Gs regulate?
PKA activity, via controlling cAMP levels
What receptor does Gi act on?
Inhibitory GPCR
Main steps in signal transduction pathways?
G protein
cAMP
protein kinase A
Phosphorylation events
