Lecture 2.1: Structure & Classification of Receptors Flashcards

1
Q

Why is cell signalling important?

A

It permits effective communication and regulation of cells and cellular processes

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2
Q

What are the steps in cell signalling?

A

Reception
Transduction
Response
Amplification

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3
Q

Receptors are proteinaceous, what does this mean?

A

Capable of selectively binding a ligand (therefore, responses are selective as well)

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4
Q

Receptor numbers are not static, what does this mean?

A
  • Increased numbers of receptors =
    upregulation (increased sensitivity)
  • Decreased numbers = downregulation
    (desensitisation or tachyphylaxis)
  • Desensitisation occurs after a series of doses,
    tachyphylaxis may occur after the first dose
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5
Q

What is a Ligand?

A

A molecule that binds to a receptor

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6
Q

Examples of Ligands

A
  • Hormones
  • Neurotransmitters
  • Growth Factors
  • Drugs
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7
Q

What is a ligand which binds and activates called?

A

Agonist

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8
Q

What is Agonist Potency?

A

[Agonist] needed to produce 50% maximal response

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9
Q

What is Agonist Efficacy?

A

Ability of an agonist, after binding, to activate receptors

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10
Q

What is a ligand which binds and blocks agonist binding called?

A

Antagonist

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11
Q

What is a which fails to produce maximal response on binding called?

A

Partial Agonist

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12
Q

What type of receptor is a Ligand gated ion channels?

A

Ionotropic Receptors

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13
Q

What type of receptor is a G protein-coupled receptors (GPCR)?

A

Metabotropic receptors

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14
Q

What type of receptor is an Enzyme-linked receptors?

A

Kinase-linked receptors

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15
Q

What type of receptor is an Intracellular receptors?

A

DNA-linked nuclear receptors

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16
Q

What type of receptor is a nicotinic receptor?

A

Ionotropic receptor

17
Q

What us the structure of a nicotinic receptor?

A
  • Formed from 5 subunits (2 a’s, 1
    beta, 1 gamma, 1 delta)
  • There are 2 binding sites (on a’s)
    that need to be occupied before
    the receptor is activated
18
Q

What is the role of ionotropic glutamate receptors?

A

Mediates the effects of the excitatory amino neurotransmitter Glutamate

19
Q

What are the 3 Types of ionotropic glutamate receptors?

A
  • NMDA
  • AMPA
  • Kainate
20
Q

How many subunits is the NMDA receptor made from?

A

7 subunits (monomers)

21
Q

How does the NMDA receptor work?

A

Highly permeable to Ca2+, and easily blocked by Mg2+ , receptor also requires glycine to bind

22
Q

What is the role of the NMDA receptor?

A
  • Significant roles in synaptic plasticity (learning,
    memory also though pathophysiology e.g.
    chronic pain)
  • Significant role in excitotoxicity caused by Ca2+
    overload
23
Q

Why are G-protein coupled receptors (GPCRs) called metabotropic receptors?

A
  • Because they trigger chain of intracellular
    reactions known as the second messenger system
  • The link to these second messengers are G-
    proteins hence the name!
24
Q

Examples of GPCRs (2)

A
  • Adrenoreceptors (noradrenaline)
  • Muscarinic receptors (acetylcholine)
25
Q

Why are GPCRs important in medicine?

A

They are important targets for drug action (c.50% of all modern drugs target GPCRs)

26
Q

What is the structure of enzyme linked receptors/kinase-linked receptors?

A

Have an extracellular ligand binding region and an intracellular catalytic domain (activated by binding) that is enzymatic in nature

27
Q

Why are enzyme linked receptors/kinase-linked receptors important in medicine?

A

Significant interest as drug targets to treat e.g. cancers and obesity

28
Q

Examples of enzyme linked receptors (4)

A
  • Hormone (e.g. insulin)
    receptors
  • Growth factor receptor
  • Cytokine receptor
  • Leptin receptor
29
Q

What is Autophosphorylation?

A

Autophosphorylation is a type of post-translational modification of proteins. It is generally defined as the phosphorylation of the kinase by itself.

30
Q

What are the target cells for insulins? (3)

A
  • Hepatocytes
  • Adipocytes
  • Skeletal Muscle Cells
31
Q

What is the role of insulin?

A

An anabolic hormone, hypoglycaemic (reduces plasma glucose)

32
Q

What is the structure of the insulin receptor? How does insulin bind?

A
  • Each receptor consists of a
    ligand binding region (a-
    subunit) which is linked via a
    disulphide bridge to the
    catalytic region (B- subunit)
  • A disulphide bridge then
    links two of these monomers
    together producing a
    preformed dimer to which
    insulin binds
  • Insulin then binds to
    extracellular a-subunit this
    results in
    autophosphorylation of the
    B-subunit
  • SH2 domains of IRS (insulin
    receptor substrate) family
    proteins binds to the
    receptor
33
Q

How do Intracellular Receptors act on DNA? (3)

A
  • Influence genetic expression of enzymes
  • Influence genetic expression of cytokines
  • Influence genetic expression of receptor proteins
34
Q

What drugs interact with intracellular receptors?

A
  • Sex hormones
  • Thyroid hormones
  • Mineralocorticoids
  • Vitamin D
35
Q

Steroid hormones pass through the cell
membrane with ease, though transporting
them to target sites is problematic, Why?

A
  • The inactive receptor forms a complex with HSP90
  • It blocks a region called the hinge site when hormone
    binds and HSP90 dissociates
  • The hormone-receptor complex enters the nucleus
  • Entry is facilitated by a nuclear localisation signal (NLS)
    that is located at the hinge site
  • Generally, dimerisation occurs and the hormone-
    receptor complex interacts with DNA to influence gene
    expression