Question 1

When comparing direct and indirect synaptic transmission, indirect synaptic transmission

Accepted Answer

Indirect synaptic transmission involves metabotropic receptors and second-messenger pathways, unlike direct transmission which typically involves ligand-gated ion channels for fast, direct effects.

Question 2

When comparing ionotropic and metabotropic receptors which of the following is true?

Accepted Answer

Ionotropic receptors mediate their effects faster than metabotropic receptors because they directly control ion channels, leading to immediate changes in the cell's ion permeability upon ligand binding. Metabotropic receptors, on the other hand, act through second messenger systems, which take longer to produce a cellular response.

Question 3

How many transmembrane domains do all G protein-coupled metabotropic receptors have?

Accepted Answer

All G protein-coupled metabotropic receptors are characterized by having 7 transmembrane domains.

Question 4

Each particular metabotropic receptor (e.g., a metabotropic glutamate receptor)

Accepted Answer

Metabotropic receptors can couple to a variety of G proteins, allowing them to influence multiple signaling pathways within the cell. This flexibility is key to the diverse roles metabotropic receptors play in modulating cellular responses to external signals.

Question 5

When different transmitters or hormones act through different G protein-coupled metabotropic receptors,

Accepted Answer

Multiple receptors can indeed be coupled to the same type of G protein, allowing for diverse signaling pathways to be activated by different ligands through the same G protein.

Question 6

The G proteins that coupled to metabotropic receptors are

Accepted Answer

G proteins that are coupled to metabotropic receptors are heterotrimeric, meaning they are composed of three different subunits: α-, β-, and γ-subunits. These proteins bind GTP, not cGMP.

Question 7

For G protein-coupled metabotropic receptors, GTP binds to the

Accepted Answer

GTP binds to the α-subunit of the heterotrimeric G protein associated with G protein-coupled receptors (GPCRs). This binding is crucial for the activation of the G protein, leading to subsequent intracellular signaling events.

Question 8

How is G protein-mediated signaling terminated?

Accepted Answer

The termination of G protein-mediated signaling occurs when the α-subunit hydrolyzes GTP to GDP, causing the α-subunit to reassociate with the βγ-complex, thus inactivating the G protein.

Question 9

Which of the following tests would be effective at determining if a transmitter action was mediated by a G protein-coupled receptor?

Accepted Answer

GTP-γ-s is a non-hydrolyzable analog of GTP that can activate G proteins and prolong their active state, thus indicating the involvement of G protein-coupled receptors.

Question 10

G proteins are activated when GDP is

Accepted Answer

The answer of G proteins are activated when GDP is
...

Question 11

The particular neurotransmitter present at a synapse

Accepted Answer

The neurotransmitter present at a synapse does not directly indicate the subtype of G protein or second messenger that will be coupled to the receptor. The effect of a neurotransmitter is determined by the receptor to which it binds, and different receptors for the same neurotransmitter can be coupled to different G proteins or second messengers, leading to varied cellular responses.

Question 12

Non-hydrolysable GTP analog is an analog of GTP that

Accepted Answer

Non-hydrolysable GTP analogs are designed to resist cleavage by GTPases, meaning they cannot be converted to GDP. This property is used in research to study G protein function by preventing the inactivation of G proteins, which normally occurs through GTP hydrolysis.

Question 13

What would happen to G protein-coupled metabotropic signaling in a cell if you removed GTP from the cell cytoplasm?

Accepted Answer

G protein-coupled metabotropic receptor signaling requires GTP for the activation of G proteins. Removing GTP from the cell cytoplasm would block the signaling because G proteins need to bind GTP to become active and transmit the signal.

Question 14

What would happen to metabotropic signaling in a cell if you added cholera toxin?

Accepted Answer

Cholera toxin irreversibly activates Gs protein-coupled metabotropic signaling pathways, leading to increased cAMP levels inside the cell.

Question 15

What would happen to metabotropic signaling in a cell if you added GDP-β-s to the cell cytoplasm?

Accepted Answer

GDP-β-S is a non-hydrolyzable analog of GDP. When added to the cell cytoplasm, it binds to G proteins but cannot be replaced by GTP, thus preventing the activation of G proteins and irreversibly inhibiting G protein-coupled metabotropic signaling.

Question 16

What would happen to metabotropic signaling in a cell if you added GTP-γ-s to the cell cytoplasm?

Accepted Answer

GTP-γ-S is a non-hydrolyzable analog of GTP, which means it can bind to G proteins but cannot be hydrolyzed to GDP. This results in the irreversible activation of G proteins and, consequently, the continuous activation of G protein-coupled metabotropic signaling pathways.

Question 17

You are recording calcium channel currents using whole cell patch clamp methods from frog sympathetic ganglia neurons with GTP-γ-s included in the patch pipet. What would happen when you added norepinephrine to the solution bathing this neuron.

Accepted Answer

Norepinephrine, acting through G-protein coupled receptors, would persistently activate calcium currents in the presence of GTP-γ-s, which is a non-hydrolyzable analog of GTP. This prevents the G-protein from turning off, leading to prolonged activation of downstream effectors such as calcium channels.

Question 18

Which of the following experiments provided experimental evidence that potassium channels in cardiac muscle cells were opened by the direct action of βγ-subunits of activated G proteins?

Accepted Answer

B) This choice is correct because it directly states that the application of pure recombinant βγ-subunit to the intracellular side of a patch in inside-out patch clamp recordings resulted in the opening of cardiac potassium channels. This provides clear experimental evidence that βγ-subunits of activated G proteins can directly open potassium channels in cardiac muscle cells.

Question 19

What would happen in muscle cells dissociated from the atrium of the heart if you added acetylcholine in the presence of an inhibitor of RGS proteins?

Accepted Answer

Acetylcholine increases potassium channel activity in heart muscle cells, leading to hyperpolarization and a decrease in heart rate. RGS proteins normally accelerate the termination of G protein-coupled receptor signaling. Inhibiting RGS proteins would prolong the effect of acetylcholine, thus increasing potassium channel activity for a longer duration than normal.

Question 20

What does it mean that inhibition of calcium channels by norepinephrine is "voltage-dependent"?

Accepted Answer

The term "voltage-dependent" in this context means that the effect of norepinephrine on calcium channels changes with the membrane potential. Specifically, the inhibition is reduced when the membrane is depolarized.

Quiz 12: Indirect Mechanisms of Synaptic Transmission