M&R Session 6- Structure Of Receptors- Common Structural Motifs

Question 0

What is endocrine signalling?

Answer 0

Hormone release by a signal cell goes into the bloodstream and acts on a target cell.

Question 1

What is paracrine signalling?

Answer 1

The release of a local chemical mediator by one cell then effects nearby cells of the same tissue.

Question 2

What is synaptic signalling?

Answer 2

The neurotransmitter released by the presynaptic bouton travels across the synapse and acts on the post synaptic membrane receptor.

Question 3

What type of signalling molecule can cross the plasma membrane and bind to intracellular receptors? Give an example.

Answer 3

Hydrophobic.

Steroid hormones and thyroxine

Question 4

What type of signalling molecule requires a cell surface receptor?

Answer 4

Hydrophilic

Question 5

Define receptor

Answer 5

A molecule that recognises specifically a second molecule (ligand) and that brings about regulation of a cellular process as a result of its binding.

Question 6

When is a receptor silent?

Answer 6

In the unbound state

Question 7

Define ligand

Answer 7

A molecule that specifically binds to a receptor.

Question 8

When is a ligand an agonist?

Answer 8

When its binding brings about activation of the receptor

Question 9

When is a ligand an antagonist?

Answer 9

When its binding doesn’t cause activation, but prevents an agonist from binding.

Question 10

What is an acceptor?

Answer 10

A molecule often classed as a receptor.

It can however, function without the binding of a ligand.

Question 11

Why is the ligand binding to receptors of higher affinity that substrate binding to enzymes?

Answer 11

Receptors can detect their ligand a at lower concentrations.

Question 12

What is the agonist of nicotinic and muscarinic receptors respectively?

Answer 12

Nicotine and muscarine

Question 13

What is the highest affinity antagonist of M1 receptors?

Answer 13

Pirenzipine

Question 14

What is the antagonist of M2 receptors?

Answer 14

Gallamine

Question 15

What is antagonist of M3 receptors?

Answer 15

Hexahydrosiladiphenol

Question 16

What are the similarities between receptor binding sites and active sites of enzymes?

Answer 16

• binding at both is specific
• specificity of binding is governed by the shape of the binding site
• binding to both is often reversible
• induce a conformational change
• there is no conformational change of the ligand/ substrate

Question 17

What are the differences between receptor and enzyme binding?

Answer 17

-affinity of ligand binding compared to substrate binding is higher.

Question 18

What is auto phosphorylation?

Answer 18

When the binding of an agonist to the extracellular receptor site activates protein kinase and causes the receptor to phosphorylate tyrosine residues on its partner receptor.

Question 19

What are the 4 signal transducers of hydrophilic signals to intracellular events?

Answer 19

1. Membrane bound receptors with integral ion channels
2. Membrane bound receptors with integral enzyme activity
3. Membrane bound receptors without enzymes or ion channels (7tmdr)
4. Intracellular receptors

Question 20

Give an example of a membrane bound receptor with integral ion channel and explain how it works

Answer 20

nAChR - binds to 2 alpha subunits which causes conformational change and opening of the channel, allowing sodium and potassium ion movement.

Question 21

Give an example of a membrane bound receptor with integral enzyme activity and briefly explain how it works

Answer 21

Tyrosine kinase-linked receptor
Binding of an agonist to extracellular site causes conformational change that activates protein kinase enzyme.
This auto-phosphorylates tyrosine residues on the receptor.
These phosphorylated tyrosine are recognised by a transduction protein or enzymes.

Question 22

Explain how membrane bound receptors with no enzyme or channel activity work. - 7 transmembrane domain receptors

Answer 22

They are coupled to G proteins.
The binding of a receptor causes a conformational change which activates GDP/GTP exchanged in G proteins. They then transduce the message to an enzyme/channel in the membrane.

Question 23

Give an example of an intracellular receptor and explain their mechanism

Answer 23

Steroid hormones
They are hydrophobic therefore cross the plasma membrane and bind to intracellular receptors in the cytoplasm or nucleus.
Then bind to DNA binding site and regulate gene expression

Question 24

How does amplification of a signal occur?

Answer 24

Stimulating enzyme activity

Question 25

What does noradrenaline bind to in cardiac pacemaker cells to increase heart rate?

Answer 25

Beta -1 adrenoceptors

Question 26

What does ACh bind to in cardiac pacemaker cells to decrease heart rate?

Answer 26

M2 muscarinic receptors