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SL12010 Health and Disease Flashcards > Receptors, Agonists and Antagonists: Lectures 14 - 17 > Flashcards

Receptors, Agonists and Antagonists: Lectures 14 - 17 Flashcards

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1
Q

What are the four main protein targets for drug action?

A
  • Receptors
  • Ion channels
  • Enzymes
  • Transporters
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2
Q

What is an ion channel blocker?

What is an ion channel modulator?

A

A compound which blocks a given ion channel preventing ion movement.

A compound which modulates (inc/dec) the behaviour of an ion channel.

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3
Q

What is an ion channel modulator?

A

A compound which modulates (inc/dec) the behaviour of an ion channel.

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4
Q

What is an ion channel blocker?

A

A compound which blocks a given ion channel preventing ion movement.

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5
Q

Summarise the ways in which a drug can utilise/manipulate ion channels:

A

Ion channels can be:

  • Blocked
  • Modulated
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6
Q

State the function of an ion channel:

A

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

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7
Q

State the function of an enzyme:

A

To act as a biological catalyst, accelerating chemical reactions.

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8
Q

Summarise the ways in which a drug can utilise/manipulate enzyme function:

A

A drug can:

  • Inhibit an enzyme
  • Act as a false substrate
  • Be a prodrug that is metabolised by said enzyme
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9
Q

What is a false substrate compound?

A

A compound which when catalysed by an enzyme, forms an abnormal or altered metabolite which interferes with the typical metabolic pathway.

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10
Q

What is an inhibitor compound?

A

A compound which when bound to an enzyme, prevents the enzyme from catalysing reactions, thereby reducing enzyme activity.

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11
Q

What is a prodrug compound?

A

A compound which when catalysed by an enzyme, forms an active drug molecule inside the body (often to bypass a drug-eliminating metabolic system or to improve absorption).

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12
Q

What is the function of a transporter?

A

To move specific substances against a concentration gradient by active transport using energy.

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13
Q

In what way is a transporter distinct from a channel protein?

A

A transporter works via active transport and is not open to both sides of a membrane.

A channel protein works via facilitated diffusion and is open to both sides of a membrane.

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14
Q

Summarise the ways in which a drug can utilise/manipulate a transporter:

A

Drugs for a transporter can be a(n):

  • Inhibitor
  • False substrate
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15
Q

What is the function of a receptor?

A

To respond to an exogenous cue and relay a signal into a cell to produce a response.

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16
Q

What is the main drug target?

A

Receptors.

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17
Q

Why are receptors the most common drug target in the human body?

A
  • They’re very specific, minimising side effects
  • Wide variety of actions upon binding
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18
Q

What are the three types of drugs that interact with receptors? Explain how they function.

A

Agonists: Activate the receptor
Antagonists: Block the receptor
Modulators: Inc/dec receptor activation

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19
Q

What are the three receptor states? What do they mean?

A

Inactive: Receptor is unbound and producing no response

Bound: Receptor is bound but not yet producing a response

Active: Receptor is bound and producing a response

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20
Q

Describe how ligand-receptor interactions initiates an intracellular response:

A
  • Ligand binds to receptor
  • Causes conformational change in the receptor
  • Shape change of the internal portion of the receptor leads to a response
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21
Q

What are the four main types of receptors?

A
  • Ligand-gated ion channels
  • G protein-coupled receptors (GPCR)
  • Kinase-linked receptors
  • Nuclear receptors
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22
Q

Explain how ligand-gated ion channels function:

A
  • Act like regular ion channels opening to allow the passage of a given molecule
  • Open and close in response to ligand binding
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23
Q

Provide an example of a process that uses ligand-gated ion channels:

A

Nicotinic receptors at synapses open ion channels when bound by ACh.

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24
Q

Explain how kinase-linked receptors function:

A
  • Receptor split in two monomer halves in the membrane when inactive
  • Ligand-receptor engagement dimerises the receptor proteins
  • Activates kinase activity
  • Initiating downstream cascade and biological response
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25
What is a kinase? What are they used for?
An enzyme which phosphorylates its target via ATP. Used to in essence turn a target on/off.
26
Provide an example of a process that uses kinase-linked receptors:
- Epidermal growth factor receptor promotes cell growth and is found in the lungs - Lung cancers express more EGFRs = more growth - These cancers are susceptible to EGFR targeting drugs
27
What is a G-protein coupled receptor? What is its function?
A receptor coupled to a G protein which, when ligand bound, activates the G protein thus eliciting an intracellular response.
28
Describe the general structure of a GPCR:
- Receptor with 7 transmembrane domains - Coupled to G protein - Different GPCRs coupled to different G proteins
29
When talking about GPCRs, what is nucleotide exchange?
The process wherein GDP and GTP are exchanged on a G protein in order to cause an intracellular response.
30
Summarise the process of nucleotide exchange in a GPCR:
1. GPCR in resting state 2. Ligand binds causing GDP to be exchanged for GTP on the G protein 3. GTP bound G protein interacts with effector 4. GTP hydrolysed to GDP, G protein dissociates from effector
31
Provide an example of a process that uses GPCRs:
- M3 GPCRs present on intestinal smooth muscle - When bound to initiates peristaltic contractions - Antimuscarinics for M3 GPCRs can reduce this peristalsis
32
What is the function of a nuclear receptor?
To diffuse into the nucleus when bound by a ligand and alter gene expression.
33
Give an example of a nuclear receptor:
Oestrogen receptors: - Oestrogen binds to oestrogen receptor - Diffuses into nucleus - Increases expression of sexual maturation genes
34
What is an agonist?
A ligand which activates a receptor when it binds.
35
What two factors are used to measure the response of an agonist?
- Affinity - Efficacy
36
Define affinity in relation to agonist response:
Affinity describes how well a drug binds to a receptor.
37
Define efficacy in relation to agonist response:
Efficacy describes how well a drug activates a receptor.
38
What does Emax measure?
Agonist affinity
39
What does EC50 measure?
Agonist efficacy
40
If two drugs have the same Emax but different EC50 what conclusion can be made about the drugs?
The drugs have the same affinity but different efficacies.
41
If two drugs have the same EC50 but different Emaxs what conclusion can be made about the drugs?
The drugs have the same efficacy but different affinities.
42
When discussing potency what factor of the drug is being measured?
The efficacy of the drug.
43
What is a partial agonist?
An agonist which produces a partial response in a biological system, less than the full response the body is capable of producing.
44
What is an inverse agonist?
An agonist which reduces the basal level of activity upon binding.
45
What is biased agonism?
When different agonists produce different effects through the same receptor.
46
How may biased agonists produce different effects?
- By promoting different activation states - Which use different secondary messengers - Which generate different responses
47
What is a competitive antagonist?
A ligand that competes with an agonist for the same receptor binding site?
48
What is meant by a competitive antagonist being reversible or irreversible?
Reversible: Increasing agonist conc can outcompete antagonist Irreversible: Antagonist permanently binds to receptor
49
How do reversible competitive antagonists affect the dose response curve?
Curve shifted rightwards, increasing EC50 value and decreasing efficacy whilst Emax stays the same.
50
How do irreversible competitive antagonists affect the dose response curve?
Response to dose is reduced, causing Emax to decrease (primarily) and EC50 to increase (secondarily).
51
How is antagonism quantified? Outline the process.
By producing a Schild plot and determining the pA2 value: - Determine the EC50 with and without the antagonist present - Calculate the dose ratio - Plot log(DR-1) against antagonist concentration - Identify where the plotted line crosses the x axis (antagonist conc.)
52
What is the formula for dose ratio?
DR = EC50 with antagonist/EC50 without antagonist
53
How do you determine the pA2 value from a Schild plot?
Identify where the plotted line crosses the x-axis, that will be your pA2 value
54
State the pA2 equation. What does a high pA2 value signify?
pA2 = log(DR-1) - log[antagonist] High pA2 value signifies a more potent antagonist, vice versa for a lower pA2 value.
55
What is implied by two antagonists having the same pA2 value?
They affect the same receptor.
56
Describe how the shape of a Schild plot indicates the nature of antagonism:
If competitive then the relationship between log(DR-1) and log[antag] is linear. If non-competitive then the relationship is exponential.
57
Define orthosteric and allosteric:
Orthosteric: Relating to the primary site Allosteric: Relating to a secondary site (a site other than the active site)
58
What is an allosteric modulator? Describe how it may modulate.
A compound which binds to a receptor at a site other than the active site, modulating the behaviour of the receptor in some way. - Affinity modulation - Efficacy modulation - Allosteric agonism
59
Describe the three effects that an allosteric modulator may have:
Affinity modulation: Affects the capability for the agonist to bind to the orthosteric site Efficacy modulation: Affects the capability for the agonist to activate the orthosteric site Allosteric agonism: Either activates the receptor or pushes it towards activating
60
How would positive and negative affinity modulation influence the dose response curve of a given agonist?
Positive: Shift the curve to the left (lower conc required to achieve same response) Negative: Shift the curve to the right (higher conc required to achieve same response)
61
How would positive and negative efficacy modulation influence the dose response curve of a given agonist?
Positive: Stretches the curve vertically (greater maximal response and lower conc required to achieve same response) Negative: Squashes the curve vertically (lower maximal response and greater conc required to achieve same response)
62
What is another term for a negative efficacy modulator? [Think about the effect of the modulator and what it resembles]
Non-competitive antagonist
63
What is another term for non-competitive antagonism? [Think about the effect of the modulation and what it resembles]
Negative efficacy modulation
64

SL12010 Health and Disease Flashcards (18 decks)

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