receptor mech 1

Question 1

what are the 4 main types of receptors

Answer 1

• Ligand gated ion channel, tyrosine kinase linked, G protein coupled and nu
  clear/steroid receptor.

Question 2

why do nucleur receptors take the longest

Answer 2

Nuclear receptors takes the longest because its altering gene expression.

Question 3

describe the ligand gated ion channel receptor superfamily.

Answer 3

• Produce fast responses
• These receptors are a combination of proteins that create an aqueous pathway through the fatty membrane.
• This ion channell does not allow the movement of ions until two molecules of agonist have bound.
• The binding of agonist causes the chanel to open and dilate which results in ionic flow.
  So the receptor is an ion channell which only opens when the agonist binds to it.

Question 4

WHAT ARE THE 4 main types of ligand gated ion chanel receptors, their ions their effects on membrane potential and their agonist.

Answer 4

Question 5

how many proteins form a ligand gated ion chanel receptor

Answer 5

5 similar proteins -pentamer

Question 6

describe the structures of ligand gated ion channels.

Answer 6

Requires ligand binding sites and an aqueous pathway.

Made from 5 similar proteins (pentamer) with the blue region in the middle.

Each protein has 4 transmembrane domains so there’s a total of 20 TMs.

The 2nd transmembrane domain (blue) is the stretch of amino acids that contributes to the ionic pathway and where the ions move through.

if the protein is located in the membrane, some of the amino acids prefer to be in the aqueous phase and the hydrophobic amino acids would prefer to be in the lipid phase. these are the aas that traverse the membrane and form the 4 transmembrane domains.

the nature of the amino acids dictate the structure of the proteins which thus confers function

Question 7

why is there much diversity in the subunit composition in ligand gated ion channel receptrs.

Answer 7

this is because Whilst there are only 4 members of the super family , there are a number of different gene products that comprise each receptor. The receptors can be slightly different depending on the molecular compostition.

Question 8

how many molecules must bind for receptor activation

Answer 8

2

Question 9

where are the nACHR located

Answer 9

skeletal muscle, cns, automomic ganglia

Question 10

what is the composition of the nachr in the brain

Answer 10

In the brain, the nicotine acytlcholine receptors comprises of a combination of alpha2-alpha8 and beta2-beta4. there are always 2 alphas because they comprise the acetly choline binding domain.

Question 11

what is the composition of the nACHr in the skeletal muscle.

Answer 11

In the skeletal muscle , there are 2 alpha 1s, a beta1 and 2 deltas which can be in combination with an episilon or a gamma depending on whether the skeletal muscle is from an adult or foeutus. As we develop, the nicotine acetyl choline receptor changes the proteins that are present in the receptor complex, going from a gamma to an epsilon, which results in the different binding of the acytl choline and different opening properties.

Question 12

where does the acetly choline bind to in a Nachr

Answer 12

The acrtlycholine sits in the groove of the alpha subunit

Question 13

why does receptor activation allow ion flow.

Answer 13

The binding of 2 molecules of actylcholine causes a molecular kink that increases the size of the internal pore and allows sodium or calcium influx, leading to membrane depolarisation

on which leads to for example activation of skeletal muscle.

Question 14

describe how nachr are activated

Answer 14

Initially the motor neurone isnt depolarised but due to random collisions occuring all the time, there is some leakage of ACH.

Motor nerves are activated and acetlycholine is released . There is a short diffusion pathway and 2 molecules of acetly choline bind to the alpha subunits. There are 5 proteins that bind to the alpha subunits which leads to the rapid opening of the ionic pathway and an influx of sodium down the elctrochemical gradient so membane potential changes from -70 to -50. This causes an excitatory junction potential . It takes the membrane potential to a threshold where voltage gated sodium chanels open up. The membrane potential of skeletal muscles depolarise and more sodium chanels are activated.

As soon as the acetlycholine unbinds, the ion chanel closes and the membrane potential returns to -70 .

When the acetylcholine dissociates from the receptors and is brokendown by choline esterases, the sodium channels close and resting potential is reached agin

Question 15

where does myaesthesia gravis affect

Question 16

what is myaethesia gravis.

Answer 16

An autoimmune disease caused by the muscle nicotine AChRs being degraded due to the a1 subunit. The a1 subunit becomes immunogenic and the body creates antibodies against it to degrade it. ·It causes muscle weakness, drooping eyelids, fatigue, difficulty swallowing/talking and difficult exertion. ·The neuronal nicotine AChRs are unaffected and it doesn’t cause neurological problems because it only targets the a1 subunit

Question 17

compare the action potentials of a normal nmj and one of a patient with myaesthia gravis.

Answer 17

So at the top, stimulate the motor nerve results in the EJP potential which gets the threshold, sodium channel open which leads to action potential

At rest, the mepps form because the motor nerves are sporadically releasing acetly choline which bind to nicotine acetly choline receptors which leads to depolarisations.

In the skeletal muscle from someone suffering from myaesthesia gravis, there are no mepps. When the motor nerve is stimulated, there is no EJP which means that an action potential does not occur.

Question 18

what are fast responses in our mediated by?

Answer 18

nachr

Question 19

do all ligand gated ion channels have the same structure.

Answer 19

ligand gated ion channel receptors that all have the same structure irrespective of what the agonist is

They consist of 5 similar proteins that come together to form an aqueous pathway through the membrane.

Each of these 5 proteins go in and out of the membrane 4 times, so there are 4 transmemebrane domains, and the second one is what lines the pore.

Question 20

what kind of nACHr tend to occur and what kind tend not to occur

Answer 20

• homomeric nAChRs tend not to occur, but heteromeric nAChRs do

Question 21

why do liganf gated ion channel receptors mediate fast responses.

Answer 21

roteins that come together to create an aqauous pathway that only opens when two molecules of agonist bind, allowing influx.

Question 22

what is a chemical response dictated by