Lecture 17 - What is a receptor? Types and function Flashcards
Name the four main proteins which drugs target
receptors
ion channels
enzymes
transporters
Where are ion channels found?
on membranes
When do ion channels open?
in response to an environmental cue, such as depolarisation of the membrane
What is the role of ion channels?
To allow the passage of channel-specific ions down the concentration gradient
Name and describe two categories of drug which act on ion channels
- blockers = prevent ion movement through the ion channel
- modulators = increase/decrease the chance of the channel opening
Give an example of a drug which is a blocker that acts on ion channels
lidocaine - blocks voltage gated sodium ion channels
Give an example of a drug which is a modulator that acts on ion channels
Gabapentin - reduces the activity of voltage-gated calcium channels
What is an enzyme/ what is their role?
To act as biological catalysts and speed up chemical reactions
they mediate biochemical signals within cells and tissues
Name the three categories of drugs which act on enzymes
inhibitors
false substrate
prodrug
Effect of inhibitor on enzyme
give an example
prevent activity
aspirin- a cyclooxygenase inhibitor
Effect of false substrate on enzyme.
Give an example of a drug
abnormal metabolite is produced
fluorouracil used for chemotherapy
Effect of prodrug on enzymes.
give example of a drug.
activation of drug molecules - for example codeine is converted into morphine by the enzyme.
What is the role of transporter proteins?
transport/carry substances across membranes against the concentration gradient by active transport.
Difference between channel and transporter proteins.
channel protein open at both sides of membrane at once. Transporters do not.
The two types of drugs which act on transporter/carrier proteins are…?
inhibitor and false substrate
Describe the effect of inhibitor drugs on transporters. Give an example
inhibitors block transport. For example, fluoxetine is a serotonin transport blocker
Describe the effect of false substrate on transport proteins. Give example.
abnormal compound accumulates
For example, amphetamine acts on dopamine and noradrenaline transporters.
Where are receptors found?
cell membranes
What is a receptor?
proteins found on the surface of cell which receive and transduce signals
How do receptors work?
Something binds to receptor and the receptor responds to this exogenous cue and relays a signal into a cell to produce a response
Name three types of drugs which act on receptors
agonist, antagonist and modulator
What is an agonist drug and give an example.
A drug which binds to receptor (a ligand) which induces a response.
For example, morphine activates opioid receptors.
What are antagonist drugs? Give an example.
Antagonist bind to receptors (ligand) and block the receptor, preventing activators from binding to it.
Example: naloxone blocks opioid receptors
ligand
something that binds
What is a modulator drug’s effect on receptors? Give an example.
these bind elsewhere on receptor and increase/decrease its ability to activate and relay signal into the cell.
example- diazepam. This enhances GABA receptor activation
second messenger
relays signal from receptor to effector
signal transduction
sequence of second messengers that elicit a biological response.
Name 4 types of receptors.
- Ligand gated ion channels
- G protein coupled receptors
- Kinase linked receptors
- Nuclear receptors
Ligand gated ion channels- a type of receptor are unlike other ion channels such as voltage gated. Why?
they require an agonist to be opened.
How do ligand gated ion channels work?
A ligand binds and opens the ion channels, allowing movement of channel specific ions
Give an example of a ligand gated ion channel- a receptor, whose ligand is acetylcholine.
Electrical impulse travels down the pre-synaptic neurone, the vesicles containing acetylcholine fuse with the pre-synaptic membrane, acetylcholine is released into and move across the synaptic gap, bind to receptors (nAChRs)- the ion channels- on post-synaptic membrane, opening the ion channels, this allow sodium ions to move from outside of the neuron to inside of the neuron, triggering an impulse.
What are kinase? How do they work?
- second messengers. They relay signals from receptor to the effector
- enzymes which use ATP to add phosphates onto targets.
- they take target proteins and add a phosphate group onto the protein by ripping a phosphate molecule from ATP, forming ADP.
- Cells use kinase as a switch. By phosphorylating a target protein, you can turn it on or off. It also allows other second messengers to bind
What is a kinase-linked receptor/how do they work?
Kinase-linked receptors are split in two halves in the membrane (two monomers). When something binds to them, the two halves/two receptor proteins come together and form a ‘dimer’. The kinase is then activated and can then phosphorylate the target. This initiates a biological response.
Give an example of kinase- linked receptors and how it can go wrong and a drug used to treat the condition.
epidermal growth factor receptor is a type of kinase-linked receptor. EGFR can promote cell growth. Lung cancer cells express more EGFR proteins compared to a normal cell, causing more growth. Drugs can target EGFR- targeted therapy- this shuts down the cancer growth.
Describe structure of G protein coupled receptors.
Receptor with 7 transmembrane domains- forms a coil either side of the cell membrane. Coupled to a G protein.
How do G protein receptors work?
Ligand binding activates G protein bound to the receptors. This interacts with the effector.
Different G protein-couples receptors are coupled to different G proteins which means…
they create different effects.
Describe effect of acetylcholine on GPRCs in the intestinal smooth muscle cells and how IBS can be treated.
Signal comes down neutrons, vesicles containing acetylcholine release into synaptic gap. Acetylcholine binds to GPRCs on intestinal smooth muscle cells. These increase calcium entry, increasing contraction. Drugs called antimuscarinics are used for irritable bowel syndrome and target these receptors.
How are nuclear receptors different to other receptors?
These are not associated with cell membranes
Describe how nuclear receptors work .
Ligand enters cells and binds to receptor in the cytoplasm. Ligand receptor complex moves into nucleus. Acts on gene expression
Describe how the nuclear receptor- oestrogen receptor can cause breast cancer. Explain the drug used to treat this.
Some types of breast cancer cells express more oestrogen receptors leading to more growth- cancerous breast cells. Tamoxifen is a drug which targets the oestrogen receptors.
