Receptors and signalling

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how do drugs exert their action

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how do drugs exert their action

by binding to proteins

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4 classes of proteins targeted by drugs

ion channels, enzymes, ion channels receptors

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what are ion channels

protein channels in the membrane that allow lipophobic /hydrophilic molecules through

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which ion channels to drugs target

involved in neurotransmission

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examples of drugs that target neurotransmission

sodium channel blockers

gabapentin

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how does gabapentin work

targets voltage gated calcium ion channels to prevent its movement and prevent AP

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role of receptor targeting

regulates cellular processes

enables communication between cells

enables coordination of tissue, organ and bodily responses

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how do drugs causes side effects despite being targeted

off target effects can occur which occurs from interactions with receptors in multiple organs

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what is an example of a drug and its side effects

opium has analgesic and euphoric effects but can cause constipation and respiratory diseases

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how does opium use lead to addiction

activation of reward pathways and changes in receptor function (tolerance)

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what is the cause of death in opium addicts

respiratory disease and suffer from chronic constipation

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how do receptors help in drug function

allows for specificity in drug function

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which type of receptor does not pass through the membrane

steroid

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what do ionotropic, metabotropic and kinase linked receptors have in common

they are found on the cell surface and have transmembrane spanning segments of 20-25 hydrophobic amino acids

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what is a feature and function of DNA linked receptors

regulates gene transcription

ligand must be able to cross the plasma membrane (lipophillic)

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what is an example of a DNA linked receptor

oestrogen receptors

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what is a ligand

any molecule that binds to the receptor

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what is a Agonist

drugs or chemical mediators that bind to a receptor producing a response

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examples of agonists

pilocarpine, nicotine, aCh, morphine

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what is an antagonist

does not a cause a downstream response or prevents/ inhibits the response of an agonist e

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examples of antagonists

atropine curare

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how long is the signal transduction of ionotropic, metabotropic, kinase-linked and nuclear receptors

mms, s, hrs, hrs

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what is an example of a LGIC

nicotinic ACh receptor

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what is an example of a metabotropic receptor

Muscarinic ACh receptor

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what is an example of a kinase-linked receptor

cytokine receptor

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what is an endogenous receptor

a compound naturally produced by the body which binds and activates the receptor

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what is the endogenous molecule for ionotropic receptors

small molecule chemical mediators not proteins

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what happens when a molecule binds to an ionotropic receptor

central aqueous pore opens

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how many transmembrane domains in GPCRS

7

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what structure do GPCRs have

alpha helical structure

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what is a heterotrimeric GTP binding protein

g protein

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when do lignad gated ion channels open

when they are bound by an agonist

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what does activation of an ionotropic receptor by excitatory neurotransmitters cause

membrane depolarisation and action potential firing

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where are nicotinic acetylcholine receptors found?

neuromuscular junction, autonomic ganglion neuron, brain neurones

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what is the agonist for NaChR

ACh and nicotine

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what is the antagonist for NaChR

tubocurarine (curare)

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examples of ionotropic glutamate receptors

AMPA and NMDA

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what are the 2 most common receptors

ligand gates and G protein coupled

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what are most hormones detected by

GPCRs

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what is the structure of GPCRs

a single protein and spans the membrane 7 times

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how do GPCRs work?

regulate effector proteins via heterotrimeric GTP binding protein

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what is the structure of a g protein

1 alpha, 1 beta, 1 gamma (heterotrimeric)

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how does signal transduction occur in GPCRs

via activation of g proteins

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how are g proteins selective

they can be made up of 30 different alpha, beta and gamma units to make different g proteins which interact with different GPCRs and effectors

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how many members of the GPCR family are there

800+

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what do GPCRs respond to

hormones, inflammatory mediators and chemokines

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why does GPCR signal transduction take longer than LGIC?

it is cascading and involves changing the function of different proteins

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where is the ligand binding site in an opioid receptor

buried within the transmembrane receptors

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what happens when the ligand is bound to a GPCR

it will make contact with several amino acids which influences the structure that the receptor will adapt

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which effectors can g proteins control

ion channels, enzymes

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types of ligand gated ion channels

cys-loop

ionotropic glutamate

P2x

calcium release

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examples of cyc-loop type receptor & assembly

nAChR, GABAa 5HT3

pentameric

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exmales of ionotropic glutamate type receptor and assembly

NMDA

tetrameric

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example of P2X type receptor and assembly

P2XR

trimeric

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examples of calcium release type receptor and assembly

IP3R, RyR

tetrameric

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what are LGIC used for

fast synaptic transmission

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what are the endogenous agonsists for LGIC

fast classical neurotransmitters stored in vesicles

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what are LGIC composed of

3-5 subunits

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how many transmembrane domains does each LGIC subunit have

2-5

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when does a LGIC close

when the agonist is removed or the receptor enters a desensitised state

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what causes changes in the excitability of a cell

ions flowing through open LGIC

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what happens in the activation of ionotropic receptors for inhibitory neurotransmitters

membrane depolarisation is inhibited

action potential firing is reduced

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what is an example of a receptor for an inhibitory neurotransmitter

GABAaRs expressed by the brain w

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what is the agonist for GABAaRs

GABA, phenobarbitone

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what is the antagonist for GABAaRs

Picrotoxin

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what is phenobarbitone used for

epilepsy

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what is the use of picrotoxin

CNS and respiratory system stimulant

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what is myasthenia gravis

an autoimmune disease where the body creates antibodies to skeletal nicotinic acetylcholine receptors

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what are the symptoms of myasthenia gravis

increasing muscle weakness, eye drooping

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how many people suffer with myasthenia gravis

1 in 2000

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how is myasthenia gravis treated

anti-cholinesterase to prevent the breakdown of ACh, and immunosuppressants

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example of an anticholinesterase

neostigmine, pyridostigmine

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why are some GPCRs referred to as orphans

because the ligand they respond to has not been identified

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when does signal transduction occur

following an agonist binding to a GPCR and activation of a g protein

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one G protein is used by _______ receptor

more than one

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how do g proteins achieve signal transduction

by undergoing an enzymatic cycle

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which g protein subunits interact with effectors

alpha and beta

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what happens when the agonist is bound to the GPCR

it stabilises the helices and activates signalling

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what happens when the antagonist is bound to the GPCR

it interacts differently with amino acids and adopts a shape not conducive to signalling

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what happens after agonist binding to GPCRs

signal transduction via g proteins which control the function of effectors

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how many types of g proteins are there

20

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what are second messengers

small diffusible molecules that spread signals

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how do noradrenaline and adrenaline work

via g protein coupled receptors

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where is the binding site of the g protein

the alpha subunit

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