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Principles > Receptors > Flashcards

Receptors Flashcards

1
Q

What kind of molecules target receptors?

A

Neurotransmitters
Hormones
Mediators eg peptide growth factors and chemokines
Therapeutic agents ie agonists, antagonists, allosteric modulators

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2
Q

Why do cells respond differently to the same ECF?

A

Different types of cells have different receptors in their membranes which have different ligands

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3
Q

What are the four main classes of receptors?

A

Type 1 - ligand-gated ion channels (LGICs)
Type 2 - G-protein-coupled receptors (GPCRs)
Type 3 - kinase linked
Type 4 - nuclear

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4
Q

What are ionotropic receptors?

Also known as transmitter-gated ion channels

A

Ligand-gated ion channels

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5
Q

What are metabotropic receptors?

A

G-protein-coupled receptors

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6
Q

Where are receptors found?

A

Plasma membrane
Intracellular membranes
Cytoplasm
Nucleus

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7
Q

Where are ligand-gated ion channels found?

What targets them?

A

Mostly plasma membrane, some in intracellular membranes (ER)

Hydrophilic signalling molecules (fast neurotransmitters)

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8
Q

Where are G-protein-coupled receptors found?

What targets them?

A

Plasma membrane

Hydrophilic signalling molecules (slow neurotransmitters and hormones)

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9
Q

Where are Kinase linked receptors found?

What targets them?

A

Plasma membrane

Hydrophilic protein mediators eg insulin and growth factors

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10
Q

Where are nuclear receptors found?

What targets them?

A 
In cytoplasm (move to nucleus following activation)
Hydrophobic signalling molecules (can cross plasma membrane unaided) eg steroid and thyroid hormones
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11
Q

What kind of protein makes up ion channels?

A

Transmembrane glycoprotein

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12
Q

Do ion channels require energy to allow ions to move to other side of membrane?

A

No, facilitated diffusion is passive

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13
Q

Are ion channels fast or slow?

A

Very fast, involved in rapid electrical signalling

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14
Q

What can (open) change the formation of a gated ion channel?

A

Chemical ligands
Voltage (membrane potential)
Physical stimuli (thermal and mechanical energy)

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15
Q

What are the three main types of Ligand-gated ion channels?

A

Pentamer
Tetramer
Trimer

Classified by number of subunits

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16
Q

Describe the structure of a ligand-gated ion channel?

Also known as ionotropic receptor

A

Separate glycoprotein subunits joining to form central channel through which ions can diffuse

17
Q

What happens when a G-protein-coupled receptor is activated?

A

Signal reaches G-protein-coupled receptor
Receptor activated
Receptor activates G-protein
G-protein activates effector
Effector synthesise second messenger which targets something within the cell

18
Q

How does the speed of GPCRs compare to LGICs?

A

GPCRs much slower

19
Q

Stucture of GPCRs

What kind of protein is a GPCR?
How many polypeptides?
How many times does it span the membrane?
Do GPCRs ever work together?

A

Integral membrane protein

One polypeptide with NH2 terminus outside and COOH terminus inside

Spans membrane 7 times (3 loops inside, 2 loops outwith)

Two may function together as a dimer

20
Q

Structure of G-protein

What kind of protein is it?
How many polypeptide subunits?
What kind of binding site?
Do multiple types exist?

A

Peripheral membrane protein

3 subunits

guanine nucleotide binding site in alpha subunit which can hold GTP or GDP

yes, depending on type of alpha subunit

21
Q

How is a G-protein activated?

A

By an agonist binding to the GPCR

22
Q

What occupies guanine nucleotide binding site when G-protein not activated?

A

GDP

23
Q

What are the Ras and Ah subdomains in a G-protein?

A

Make up alpha subunit

Ras is GTPase
AH keeps nucleotide in place

24
Q

How is a G-protein attached to plasma membrane?

A

Covalently bonded lipid molecules attached to membrane and alpha and gamma subunits

25
Q

What is the beta subunit in a G-protein attached to?

A

Gamma subunit

Together they make a heterodimer

26
Q

What happens when a GPCR is activated?

A

GCPR undergoes conformational change
This change is transmitted to G-protein alpha subunit
Alpha subunit releases GDP allowing GTP to bind
Alpha subunit of G-protein separates from GCPR and from other subunits (subunit dissociation)

Now both alpha subunit and beta-gamma heterodimer can act as free signals to other structures within cell

27
Q

How is the signalling G-protein stopped?

A

GTPase changes GTP back into GDP so original form is regained

28
Q

What happens if a beta-adrenoreceptor is activated by adenaline?

A

G(s) protein activated
Stimulates adenylyl cyclase to turn ATP into cAMP
cAMP activates kinase A
Kinase A phosphorylates Ser/Thr residures in target proteins
Causes cellular effect

29
Q

What happens if a muscarinic acetylcholine receptor is activated by acetylcholine?

A

G(i) protein activated

Inhibits production of cAMP by adenylyl cyclase

30
Q

What happens if an alpha 1 adrenoreceptor is activated by adrenaline?

A

G(q) protein activated
Stimulates phospholipase C (PLC) to turn PIP2 into IP3 and DAG
IP3 opens calcium ion channel in ER membrane
Ca2+ released causing cellular effects

DAG stimulates Protein Kinase C (PKC) to phosphorylate Ser/Thr residues in target proteins also causing cellular effects

31
Q

What happens when Insulin binds to it’s kinase-linked receptor?

A

Causes autophosphorylation of intracellular tyrosine residues
Multiple adapter proteins recruited (IRS1 especially), these are also tyrosine phosphorylated
These proteins cause cellular effects

32
Q

What are nuclear receptors?

A

Ligand-gated transcription factors

33
Q

How do steroid hormones enter a cell?

A

By diffusion - they are hydrophobic and lipophilic

34
Q

What do steroid hormones do in a cell?

A

Combine with intracellular receptor in cytoplasm causing inhibitory HSP protein to dissociate from receptor
Receptor-steroid complex moves into nucleus and forms a dimer with another complex
Dimer bonds to hormone response elements in DNA
Transcription of particular gene is either switched on (transactivated) or off (transrepressed)

Principles (21 decks)

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