Chapter 5 Flashcards
What’s a receptor protein?
A protein that is sensitive to and capable of communicating some signal.
What types of receptors are there?
Ionotropic and Metabotropic
What is an ionotropic receptor?
A receptor protein that is an ion chanel
What determines if an ionotropic receptor will produce EPSP or IPSPs?
The properties of the pore of the ion channel
What is the effect of the activation of an ionotropic receptor
Immediate change in the permeability of the membrane to specific ions
What is a metabotropic receptor?
A receptor protein that is not an ion channel
What do metabotropic receptors typically trigger? What do they produce?
They typically trigger an intracellular signaling cascade that involves g proteins.
They can produce a variety of cellular effect
What is special about the effect of metabotropic signaling? Why?
They can be large but they are often delayed.
Because they rely on signaling cascades and diffusion
What are GPCRs (g protein coupled receptors)?
Metabotropic receptors
What do ionotropic receptors “turn toward” in order to mediate their effect?
ions
What do metabotropic receptors turn towards to mediate their effects?
metabolism
What does metabolism refer to?
Chemical reactions that occur inside of cells
What do activated metabotropic receptors trigger? What is the end result?
Intracellular signals to catalyze chemical reactions.
Almost anything, but usually a change in gene expression or the opening of intracellularly gated ion channels
How do most metabotropic receptors mediate their effects?
Activating g proteins
What does the name “g” protein symbolize?
That these proteins use GTP molecules, instead of ATP molecules, for the energy they need to perform chemical reactions
What happens when a g protein is bound to GTP? Why?
It is “on” or activated. Because in this state, it can trigger chemical reactions
When a g protein is bound to GTP and can trigger chemical reactions, is this state temporary? why or why not?
Yes, it’s temporary because G proteins have a natural tendancy to convert GTP into GDP
What happens when a G proteins converts GTP into GDP?
The g protein is “off” or inactive
How can G proteins let go of GDP?
It’s hard, they can only let go of it by finding an activated metabotropic receptor. They use the intracellular side of an activated metabotropic receptor to pry off their GDP molecule. When this happens the G protein is “off” or “inactived
What is the activation cycle of g proteins?
- Ligand binding to a metabotropic receptor
which induces… - Conformational change that facilitates the exchange of GDP for GTP on the a subunit of the G protein complex
- The g proteins then disassociate and diffuse away to activate downstream enzymes
- Once the GTP molecule is metabolized (GTP to GDP) the original G protein coupled receptor complex is restored
What is a G protein-gated ion channel?
An ion channel gated by G proteins
What are G proteins family?
A family of intracellular proteins that are involved in intracellular signaling cascades
Give a generalized illustration of a metabotropic GPCR receptor causing ion channel opening.
- Neurotransmitter binds to a metabotropic receptor
- Activated G proteins transmit the message intracellularly
- Some ion channels are gated (directly or indirectly) by activated g proteins
What can G protein signaling cascades affect?
Multiple downstream processes:
-opening g protein gated ion channels
- changes in gene transcription
- secretion of substances from the cell
… really anything the cell wants
Where can synapses from?
Between axon terminals and ….?
- Dendrites (dendritic shafts)
- dendritic spines
- Soma (cell body)
- Other axon terminal (axoaxonic synapses)
What are axoaxonic synapses?
axon terminals on other axon terminals
What do axoaxonic synapses do?
Regulate the amount of neurotransmitter that the second neuron will release when it has an action potential.
What is presynaptic inhibition in axoaxonic synapses?
Axoaxonic synapses can hyperpolarize the axon terminal of the downstream neuron, so that its voltage gated calcium channels will not open at all or for very long when an action potential arrives. The effect: reduce neurotransmitter release when it has an action potential
What is presynaptic facilitation in axoaxonic synapses?
Axoaxonic synapses can depolarize the axon terminal of the downstream neuron, so that its voltage gated calcium channels are more likely to open when an action potential arrives. Effect: increase neurotransmitter release when it has an action potential
What is an autoreceptor?
A receptor located on the presynaptic membrane that gets activated when the cell releases its own neurotransmitter
What are autoreceptors gated by?
The neurotransmitter that the cell releases
Are autoreceptors generally metabotropic/ionotropic? Inhibitory or excitatory?
Metabotropic and inhibitory