receptor mechanisms 1

Question 1

what is an example of a chemical that can perform different functions

Answer 1

acetylcholine; it decreases cardiac contraction in the heart and increases contraction in the gut. it also increases the secretion of saliva in the salivary gland.

Question 2

what are two examples of ligand-gated ion channels and the agonist that stimulates them?

Answer 2

nicotinic receptor- acetylcholine
5HT3 receptor- 5HT
GABAa receptor- Gamma Amino Butyric Acid(GABA)
Glycine receptor- glycine

while there are only 4 membranes of the superfamily, there are actually a number of different gene products.

Question 3

features of a ligand gated ion channel receptor

Answer 3

they produce fast responses

they allow no movement of ions in or out of the channels until two molecules of agonists have bound to it.

receptor activation allows ion flow, and the open channel allows influx of sodium or calcium

Question 4

what is the PHYSICAL composition of LGICR

Answer 4

each LGICR is made up of 5 similar proteins and each protein goes in and out of the membrane 4 times i.e there are 4 transmembrane domains. so for each LGICR, there are (4x5=20) 20 transmembrane domains(TMDs)
in a LGICR there are some TMDs facing inwards, this is because these are the TMDs that the ion interacts with as it passes through the LGIR.

Question 5

What type of molecules pass through the superfamilies of the LGIR

Answer 5

for the nicotinic acetylcholine and the 5HT3, it is a combination of sodium and calcium coming into the cell

for GABAa and glycine receptor, it is chlorine ions going out of the cell.

Question 6

what effect does each receptor have on the membrane?

Answer 6

nicotinic and 5HT3- depolarises (because of na/ca influx) from -60 - 0V

GABAa and glycine- hyperpolarises( because of chloride influx) membrane becomes more negative.

Question 7

explain the process of activation of the nicotinic acetylcholine receptor in the skin and face muscles

Answer 7

the binding of 2 acetylcholine causes a molecular kink that increases the size of the internal pool and this leads to the influx of sodium ions leading to membrane depolarization. there is a lot of sodium ions on the outside than on the inside and 2 sodium ions bind to the receptor causing a rapid opening of the aqueous pathway and influx of sodium ions down its electrochemical gradient and this causes what is called an excitatory potential jump(EJP) and it takes the membrane to a threshold where voltage-gated channels open up.

Question 8

explain the disease myasthenia gravis

Answer 8

this is an autoimmune disease where the the alpha 1 subunit is targeted by antibodies and because of this, the muscle’s nicotinic acetylcholine receptor becomes degraded. the motor nerves are releasing lots of acetylcholine but there isn’t any receptors to bind to.

myasthenia gravis causes; muscle weakness, dropping eyelids, difficulty swallowing , talking and breathing, exertion is difficult.