Question

Which of the following is not a difference between ionotropic and metatropic receptors?

A. Number of subunits

B. Presence of channels

C. Response Speed

D. Influx of ions

E. Neurotransmitter binding site

In an experiment, a student adds a G-protein antagonist that prevents the release of GDP from the alpha subunit, to a cell. What would be the expected effect?

A. increased availability of free GDP

B. Dissociation of the alpha subunit from the beta-gamma subunit

C. decreased flow of ions through the channel

D. Initiation of signaling cascade

E. No response to transmitter binding

Answer 1

Ans 1)  Correct option is E. Neurotransmitter binding site. Both type of receptors bind to neurotransmitters and contain neurotransmitter binding site.
A. Incorrect. Both receptors differ in number of subunits. Ionotropic receptors have five protein subunits, but metabotropic receptors are large monomeric proteins.
B. Incorrect. In case of ionotropic receptors, ion channels are present but metabotropic receptors do not have ion channels.
C. Incorrect. Ionotropic receptors are fast while metabotropic receptors are slow.
D. Incorrect. In case of ionotropic receptors, there is an influx of ions when the ion channels open in response to binding of ligand but no such influx is there in case of metabotropic receptors.

Ans 2 ) Correct option is E. No response to transmitter binding.

If GDP from the alpha subunit is not released, it will not dissociate from beta-gamma subunit and will not initiate the signalling cascade. Thus, no response on binding of neurotransmitter will be there.