Lecture 17 - What is a receptor? Types and function

Question 1

Name the four main proteins which drugs target

Answer 1

receptors
ion channels
enzymes
transporters

Question 2

Where are ion channels found?

Answer 2

on membranes

Question 3

When do ion channels open?

Answer 3

in response to an environmental cue, such as depolarisation of the membrane

Question 4

What is the role of ion channels?

Answer 4

To allow the passage of channel-specific ions down the concentration gradient

Question 5

Name and describe two categories of drug which act on ion channels

Answer 5

1. blockers = prevent ion movement through the ion channel
2. modulators = increase/decrease the chance of the channel opening

Question 6

Give an example of a drug which is a blocker that acts on ion channels

Answer 6

lidocaine - blocks voltage gated sodium ion channels

Question 7

Give an example of a drug which is a modulator that acts on ion channels

Answer 7

Gabapentin - reduces the activity of voltage-gated calcium channels

Question 8

What is an enzyme/ what is their role?

Answer 8

To act as biological catalysts and speed up chemical reactions

they mediate biochemical signals within cells and tissues

Question 9

Name the three categories of drugs which act on enzymes

Answer 9

inhibitors
false substrate
prodrug

Question 10

Effect of inhibitor on enzyme

give an example

Answer 10

prevent activity

aspirin- a cyclooxygenase inhibitor

Question 11

Effect of false substrate on enzyme.
Give an example of a drug

Answer 11

abnormal metabolite is produced

fluorouracil used for chemotherapy

Question 12

Effect of prodrug on enzymes.
give example of a drug.

Answer 12

activation of drug molecules - for example codeine is converted into morphine by the enzyme.

Question 13

What is the role of transporter proteins?

Answer 13

transport/carry substances across membranes against the concentration gradient by active transport.

Question 14

Difference between channel and transporter proteins.

Answer 14

channel protein open at both sides of membrane at once. Transporters do not.

Question 15

The two types of drugs which act on transporter/carrier proteins are…?

Answer 15

inhibitor and false substrate

Question 16

Describe the effect of inhibitor drugs on transporters. Give an example

Answer 16

inhibitors block transport. For example, fluoxetine is a serotonin transport blocker

Question 17

Describe the effect of false substrate on transport proteins. Give example.

Answer 17

abnormal compound accumulates

For example, amphetamine acts on dopamine and noradrenaline transporters.

Question 18

Where are receptors found?

Answer 18

cell membranes

Question 19

What is a receptor?

Answer 19

proteins found on the surface of cell which receive and transduce signals

Question 20

How do receptors work?

Answer 20

Something binds to receptor and the receptor responds to this exogenous cue and relays a signal into a cell to produce a response

Question 21

Name three types of drugs which act on receptors

Answer 21

agonist, antagonist and modulator

Question 22

What is an agonist drug and give an example.

Answer 22

A drug which binds to receptor (a ligand) which induces a response.

For example, morphine activates opioid receptors.

Question 23

What are antagonist drugs? Give an example.

Answer 23

Antagonist bind to receptors (ligand) and block the receptor, preventing activators from binding to it.

Example: naloxone blocks opioid receptors

Question 24

ligand

Answer 24

something that binds

Question 25

What is a modulator drug’s effect on receptors? Give an example.

Answer 25

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

Question 26

second messenger

Answer 26

relays signal from receptor to effector

Question 27

signal transduction

Answer 27

sequence of second messengers that elicit a biological response.

Question 28

Name 4 types of receptors.

Answer 28

• Ligand gated ion channels
• G protein coupled receptors
• Kinase linked receptors
• Nuclear receptors

Question 29

Ligand gated ion channels- a type of receptor are unlike other ion channels such as voltage gated. Why?

Answer 29

they require an agonist to be opened.

Question 30

How do ligand gated ion channels work?

Answer 30

A ligand binds and opens the ion channels, allowing movement of channel specific ions

Question 31

Give an example of a ligand gated ion channel- a receptor, whose ligand is acetylcholine.

Answer 31

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.

Question 32

What are kinase? How do they work?

Answer 32

• 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

Question 33

What is a kinase-linked receptor/how do they work?

Answer 33

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.

Question 34

Give an example of kinase- linked receptors and how it can go wrong and a drug used to treat the condition.

Answer 34

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.

Question 35

Describe structure of G protein coupled receptors.

Answer 35

Receptor with 7 transmembrane domains- forms a coil either side of the cell membrane. Coupled to a G protein.

Question 36

How do G protein receptors work?

Answer 36

Ligand binding activates G protein bound to the receptors. This interacts with the effector.

Question 37

Different G protein-couples receptors are coupled to different G proteins which means…

Answer 37

they create different effects.

Question 38

Describe effect of acetylcholine on GPRCs in the intestinal smooth muscle cells and how IBS can be treated.

Answer 38

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.

Question 39

How are nuclear receptors different to other receptors?

Answer 39

These are not associated with cell membranes

Question 40

Describe how nuclear receptors work .

Answer 40

Ligand enters cells and binds to receptor in the cytoplasm. Ligand receptor complex moves into nucleus. Acts on gene expression

Question 41

Describe how the nuclear receptor- oestrogen receptor can cause breast cancer. Explain the drug used to treat this.

Answer 41

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.