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Biochemistry - Foundation Module > Receptors > Flashcards

Receptors Flashcards

1
Q

Define a Receptor.

A

Cellular receptors are proteins either inside a cell or on its surface which receive a signal from outside the cell and triggers an intracellular response.

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2
Q

Define a Ligand.

A

The ligand is a chemical messenger released by one cell to signal either itself or a different cell.

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3
Q

What are Second Messenger systems?

A

Intervene between the ligand (first messenger) and the ultimate intracellular response.

Take part in the cascade of events that transduces signal from the receptor-ligand complex into a specific intracellular response.

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4
Q

What is the classification for receptors?

A
  1. Cell-surface receptors/ Transmembrane receptors
  2. Internal Receptors
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5
Q

two types of internal receptors.

A
  • Cytoplasmic receptors
  • Nuclear receptors
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6
Q

Examples of Cytoplasmic Receptors

A
  • Steroid hormone receptors (androgen, glucocorticoid, mineralocorticoid)
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7
Q

Examples of Nuclear Receptors

A

retinoic acid receptors, thyroid receptors

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8
Q

Classification of transmembrane Receptors (based on speed)

A
  • Inotropic
  • Metabotropic
  • Enzyme-linked receptors
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9
Q

What are Inotropic receptors?

A
  • ligand-gated ion channels
  • Fast
  • No 2nd messenger systems
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10
Q

What are Metabotropic receptors?

A
  • e.g. G-protein coupled receptors
  • coupled to 2nd messenger systems * Slow
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11
Q

What are enzyme-linked receptors?

A
  • e.g. receptor tyrosine kinase(insulin receptor)
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12
Q

What is Receptor-Mediated Endocytosis?

A
  • A special class of receptors is involved in the uptake of certain substances; e.g. Low-density lipoprotein (LDL).
  • The receptor recognizes the LDL particle, binds to it, and mediates endocytosis.
  • The signal is the LDL molecule, and the cellular response is endocytosis, hence second 2nd messenger systems are not involved.
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13
Q

Functions of a receptor?

A
  1. Recognition;
  2. Coupling;
  3. Signal transduction;
  4. Transport
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14
Q

What is the “Coupling” function of a receptor?

A

links recognition to signal transduction

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15
Q

Features of ligand-receptor interactions?

A
  • Selectivity
  • Affinity
  • Efficacy
  • Potency
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16
Q

What is the “selectivity” function of receptors?

A

the degree to which a ligand acts on a given receptor relative to other receptors (ligands can be selective or non-selective)
- e.g. cardio-selective; act on receptors on the heart only.

17
Q

What is the “Affinity” function of receptors?

A

the extent to which a ligand binds to receptors at any given drug concentration

18
Q

What is the “Efficacy” function of receptors?

A

the amount of physiological response a given ligand imparts for a given amount of receptor occupancy

19
Q

What is the “Potency” function of receptors?

A

a measure of the amount of the ligand required to produce an effect of a given magnitude (influenced by both affinity and efficacy)

20
Q

What are the four types of receptor “Efficacy”?

A
  • (Full) Agonist
  • Partial agonist
  • Antagonist
  • Inverse agonist
21
Q

What does “Full Antagonist” Efficacy mean?

Examples?

A

Ligand that binds a receptor, producing a complete, intended response of the receptor.

salbutamol is a beta-2 receptor agonist

22
Q

What does “Partial agonist” Efficacy mean?

Example?

A

Ligand that binds a receptor, producing a partial, intended response. (both agonistic and antagonistic effects)

domperidone is a dopamine receptor antagonist

23
Q

What does “Antagonist” Efficacy mean?

Example?

A

Ligand that binds to a receptor, inhibiting/stoping the intended response of the receptor

aripiprazole has a partial agonistic effect on dopamine D2 receptors

24
Q

What does “Inverse agonist” Efficacy mean?

Example?

A

Ligand that binds a receptor, producing the opposite biological response

H1-antihistamines. E.g. chlorpheniramine (Piriton)

25
Q

What are the two main mechanisms for the regulation of receptor function?

A
  1. Regulation of receptor number
  2. Regulation of receptor activity/response
26
Q

What is the expected outcome from receptor-linked regulation?

A
  1. Increase number/activity - upregulate
  2. Decrease number/activity - downregulate
27
Q

How do you regulate receptor number?

A

Upregulation by synthesis
Downregulation by endocytosis/internalization
Downregulation by degradation

28
Q

4 Examples of regulation of receptor number by Downregulation?

A
  1. uncoupling of receptors from second messenger systems (through phosphorylation) e.g. G-protein coupled receptor
  2. Arrestins
  3. Depletion of Secondary Messenger
  4. Depletion of downstream substances due to constant activation.
29
Q

Example of regulation of receptor number by Upregulation?

A

Upregulation by the unmasking of receptors

Biochemistry - Foundation Module (8 decks)

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