Lecture 22 Flashcards
cell communication
What are the steps for signal transduction
- Reception
- Transduction
- Response
What is signal transduction
How a signal molecular cause a cellular response
what happen after a signal molecule activate the signal rec
The signal receptor switched on by a conformational change(primary transduction
What happens after the signal receptor is switched on
It will relay to a second messenger (enzymes) and start the amplification. Which then start diverting to multiple targets to cause a response.
What are the types of receptors
- ligand-gated ion channels (ionotropic receptors)
- G-protein-coupled receptor (metatropic)
- Kinase-linked receptors
- Nuclear receptors
What is the signal transduction pathway for ligand-gated ion channels (ionotropic receptors)
Ions from the extracellular will enter cell after a ligand if attached and cause a hyperpolarisation or depolarisation.
How fast does ligand-gated ion channels (ionotropic receptors) act
Milliseconds, e.g. Nicotinic, ACh receptor
Does ligand-gated ion channels (ionotropic receptors) have transduction
No, the mechanism is ion current
What does the G-protein-coupled receptor (metatropic) signal the cell
The ion channels and enzyme will open when a protein is attached to the coupled G-protein receptor. Enzyme will send a signal to the second messenger which cause cellular effects using, Ca2+ release, protein phosphorylation and others. While ion change in excitability of the cell effects
How fast a G-protein-coupled receptor (metatropic) act
seconds
what is the Kinase-linked receptors transduction pathway
Receptor or enzyme will receive the signal molecule which start the process of Protein phosphorylation > gene transcription > protein synthesis > cellular effects
what second messager are used in G-protein-coupled receptor (metatropic)
Second messenger
cAMP, cGMP, DAG, IP3
and Ca++
What is the time scale for Kinase-linked receptors transduction
hours
What are examples of Kinase-linked receptors transduction
cytokine receptor
What is Kinase-linked receptors
Receptor is an
enzyme or part
of enzyme
complex
what is the pathway of nuclear receptor
Signal molecule will enter the cell and attached the receptor which is a cytosolic or nuclear which then promote gene transcription >protein synthesis > cellular effects
What is the time scale for Kinase-linked receptors
hours
What are examples of nuclear receptor
oestrogen receptor
What receptor is Acetylcholine (ACh)
• Ionotropic receptor
Nicotinic Ach receptor
Opens Na+ ion channel
Depolarizati
What Does G protein mean
G proteins (guanine nucleotide-binding proteins,
Coupled to intracellular
effector systems via Gprot
What the steps for GPCRs
- Binding of hormone induces a conformational change in receptor
- activated receptor binds to Ga subunit
- Binding induces conformational change in Ga ; bound GDP dissociates and replaced by GTP; Ga dissociates from Gby
- Hormone dissociates from receptor; Ga binds to effector activating it.
- hydrolysis of GTP to GDP causes Ga to dissociate from effector and reassociate with Gby
What are the steps for Adrenaline/adrenergic receptor
1. G protein a subunit with GTP activates adenylyl cyclase 2. Adenylyl cyclase hydrolyses ATP to cAMP 3. cAMP binds to PKA regulatory subunit and releases the PKA catalytic unit 4. Catalytic unit is phosphorylated 5. Activated PKA phosphorylates glycogen phosphorylase enzyme 6. Glycogen broken down to glucose
What is the use of
• Proteins called b-arrest
• Proteins called b-arrestins bind to GPCR and downregulate a
response to prolonged hormone exposure (desensitization)
Inactivate GPCR
Promote removal by endocyt
What does Phosphodiesterase enzyme do
breaks down cAMP (regulatory control)
What do kinases do??
Reversible phosphorylation
What do cholera toxin do
Cholera toxin inhibits
G protein hydrolysis
-Switched on longer
What is one benefit of a G protein
It is amplification
What does caffeine do
It is a PDE enzyme inhibitor, theophylline where is inhibits phosphodiesterase from converting cAMP to 5’ AMP, thus maintaining cAMP at a high level.
Where does the phosphorus bind to in ATP kinase
tyrosine,
threonine or
serine residue
What does cholera toxin do to the cell
preventing switching off of the adenlylate cyclase
what is the effect of cholera toxin
The toxin a subunit detaches and catalyses
ADP ribosylation (addition of a ribosome unit)
of the Gas protein coupled to adenylyl cyclase
• Inhibits GTPase activity and GTP cannot be
hydrolysed back to GDP
The toxin a subunit detaches and catalyses
ADP ribosylation (addition of a ribosome unit)
of the Gas protein coupled to adenylyl cyclase
• Inhibits GTPase activity and GTP cannot be
hydrolysed back to GDP
