Neurobiology 5

Question 1

Describe the structure of a C-loop receptor?

Answer 1

Pentamers with 5 subunits, where there are Cys-Cys disulfide bridges in the N-terminal loop region.

Question 2

List 5 ligands for C-loop receptors.

Answer 2

Acetylcholine, serotonin, GABA, glycine and histidine (insects).

Question 3

Describe the structure of pore loop receptors.

Answer 3

Tetramers, where 4 subunits are assembled to form a transmembrane channel.

Question 4

Which receptor is typically larger - C loop or P loop?

Answer 4

P loop receptors.

Question 5

Describe an excitatory post-synaptic potential.

Answer 5

Sum to give an action potential once a certain threshold is reached.

Question 6

Describe an inhibitory post-synaptic potential.

Answer 6

Occurs as a result of potassium leaving the neuron and chloride ions entering the neuron.

Question 7

Describe the ‘integrate and fire’ model.

Answer 7

An excitatory and inhibitory post synaptic signal are added together to decide whether or not an action potential is fired..

Question 8

What is the inhibitory receptor in the mammalian brain?

Answer 8

GABA receptor.

Question 9

Describe a GABA receptor.

Answer 9

GABA gated chloride channel - a C loop pentameric receptor.

Question 10

What is GABA derived from?

Answer 10

The amino acid glutamate

Question 11

Give 2 examples of excitatory receptors.

Answer 11

Glutamate/AMPA receptor.

Nicotinic acetylcholine receptor.

Question 12

Describe a Glutamate/AMPA receptor.

Answer 12

Ligand gated Na+ and K+ channel (predominantly Na+).

Question 13

What type of receptor is the nicotinic acetylcholine receptor?

Answer 13

C-loop receptor - ligand gated sodium channel.

Question 14

What happens when ACh binds to the ACh receptor in muscle cells?

Answer 14

The channel opens and sodium ions move down their gradient and depolarise the muscle cell.
This AP causes Ca influx into the muscle causing actin-myosin muscle movement.

Question 15

What happens when you block ACh receptors?

Answer 15

Paralysis.

Question 16

What animal was used to determine the structure of Ache receptors?

Answer 16

An electric fish - torpedo marmorata, which specialises in generating a large electrical voltage that paralyses its prey.

Question 17

Why was the Torpedo fish selected for the structural determination of Ach receptors?

Answer 17

The muscle is packed full of acetylcholine receptors, which are almost crystalline in their native state – high quantity allows for high electrical conduction

Question 18

What is the structure of Ach receptor?

Answer 18

Five subunits come together to form a channel - alpha, beta, gamma, delta (often 2 alpha).

Question 19

What type of receptor is the GABA receptor?

Answer 19

C-loop receptor - ligand gated chloride channel.

Question 20

Is GABA a symmetric synapse?

Answer 20

Yes

Question 21

What is the post-synaptic density like in inhibitory synapses?

Answer 21

Very sparse - there are not many proteins.

Question 22

What must the pre-synaptic neuron express to be a GABAergic synapses?

Answer 22

Glutamate decarboxylase and a GABA vesicular transporter.

Question 23

What are the three different types of GABA receptors that GABAergic synapses use?

Answer 23

GABA(A), GABA(B) and GABA(C).

Question 24

What happens when GABA binds to a GABA(A) receptor?

Answer 24

The channel opens and chloride ions move down their electrochemical gradient - hyperpolarising the motor neuron.

Question 25

Why does the GABA receptor not bind Ach?

Answer 25

It contains different amino acids in its selectivity filter - making it specific to GABA. - distance between carbonyls and GABA matches hydration shell

Question 26

Describe the composition of GABA.

Answer 26

A four-carbon carboxylic acid, with an amino group at gamma carbon

Question 27

What is the function of glutamate decarboxylase?

Answer 27

Removes the carboxyl group from glutamate to form GABA.

Question 28

How many isoforms does glutamate decarboxylase exist in?

Answer 28

2

Question 29

How do glial cells involved in the reproduction of GABA?

Answer 29

Convert glutamate to glutamine, by glutamate synthase. Glutamine can then be converted into glutamate and then into GABA in neurons.

Question 30

Give an example of a drug that targets GABA(A) receptor?

Answer 30

Anti-convulsants (barbiturates) - used to treat epilepsy.

Question 31

How do these drugs affect the GABA receptor?

Answer 31

They modulate it - allowing it remain open longer/closing it.

Question 32

Where do barbiturates bind to on the GABA receptor?

Answer 32

Between alpha and beta subunit.

Question 33

What type of receptor is the AMPA glutamate receptor?

Answer 33

Pore-loop receptor - ligand gated sodium channel.

Question 34

What is the main excitatory neurotransmitter found in mammalian cells?

Answer 34

Glutamate.

Question 35

What cellular process does come from?

Answer 35

The krebs cycle.

Question 36

What happens when glutamate binds to its receptor?

Answer 36

Sodium ions influx down their gradient and depolarise the neuron (k+ ions also efflux but Na ions dominate so there is an excitatory response).

Question 37

Describe the structure of AMPA glutamate receptor.

Answer 37

Tetrameric
4 subunits - GluA1, 2, 3 and 4.
Typically heteromers.
Ionotrophic

Question 38

Define an ionotrophic receptor.

Answer 38

Receptors in which the ligand binding site is an integral part of the receptor molecule.

Question 39

Define a Mechanoreceptors.

Answer 39

Receptors that specialise in sensing mechanical forces.

Question 40

Name the domains of the ionotropic Glutamate receptor (iGluR).

Answer 40

Large N terminal domain.
Ligand binding domain.
Long C terminal domain.

Question 41

How are the domains in iGluR arranged?

Answer 41

The subunit strands twist around each other to form the glutamate receptor structure.

Question 42

Describe the ligand binding domain of iGluR.

Answer 42

Clam-like structure - when it binds glutamate it closes and causes a conformation change in the P loop.

Question 43

What happens if the knee is tapped?

Answer 43

knee jerk reflex occurs - activates stretch receptors, causing an influx of sodium ions into the sensory neuron.