Receptors in cell signalling

Question 1

Define ligand

Answer 1

Any molecule that binds specifically to a receptor

Question 2

Define agonist

Answer 2

Any molecule that binds specifically to a receptor, activating it.

Question 3

Define antagonist

Answer 3

Any molecule that binds specifically to a receptor site and does not activate it, inhibiting the action of an agonist at the site.

Question 4

Define partial agonist.

Answer 4

A molecule that binds specifically to a receptor site but can not elicit the maximum cellular response at the site, only partial.

Question 5

Give roles of receptors in physiology

Answer 5

Neurotransmission
Cellular communication
Adhesion desmasomes
Immune response

Question 6

Similarities between receptor binding sites and enzyme binding sites.

Answer 6

Both are specific to a specific molecule or family of molecule.
No chemical changes in receptor site or enzyme.
Can be reused.
Binding is transient and reversible.
Specificity governed by shape of binding cleft.
Specificity confers specific response.
Binding induces chemical change.

Question 7

Differences between receptor binding and enzyme binding

Answer 7

Receptor ligand has much lower Kd than enzyme substrate Km so much greater affinity.
Substrate is chemically altered by enzymatic binding, ligand is not.

Question 8

How are receptors classified and subclassified

Answer 8

Classified by agonist affinity

Subclassified by antagonist affinity

Question 9

What are acceptors?

Answer 9

Acceptors have activity even when ligand is not bound, constant activity that is regulated by ligand binding, not activated.

Question 10

4 mechanisms of signal transduction.

Answer 10

Receptor with integral ion channel
Receptor with integral enzyme activity
Receptor coupled to effector e.g. GPCR
Intracellular receptor that binds to DNA directly.

Question 11

Descibe membrane blue receptors with enzyme activity.

Examples

Answer 11

Single transmembrane domain
n binding terminal, C catalytic terminal
Must dimerise for function
E.g.
Tyrosine linked insulin receptor
Atrial natriuretic peptide receptor

Question 12

Describe how an insulin receptor transduces signal.

Answer 12

Hormone binds extracellularly
Dimerisation of two bound receptors
Tyrosine kinase activated in C domain
Auto phosphorylation of tyrosine residues
Phosphorylated tyrosine are recognised by transduction get proteins or by enzymes.
(or by tyrosine phosphorylation of enzyme or protein)

Question 13

Describe nAChR

Answer 13

Two ACh bind to receptors causing channel to open allowing sodium, potassium and calcium flow.

Question 14

GABA channel

Answer 14

Cl- channel

Question 15

Glycine channel

Answer 15

Cl- channel

Question 16

Glutamate receptor

Answer 16

Gated Calcium channel

Question 17

Give some non classical ion channel receptors

Answer 17

IP3
Ryanodine receptor
At

Question 18

Is intracellular receptor activation quick or slow. Why?

Answer 18

Slow as it must alter transcription and translation

Question 19

How are intracellular receptors stabilised

Answer 19

Heat shock proteins

Question 20

Describe amplification

Answer 20

Binding may activate several G proteins
G protein activates 1 protein kinase each
Each protein kinase phosphorylated many enzyme X
Enzyme X produces much product.

Question 21

Define receptor

Answer 21

A molecule that recognises and binds specifically to a ligand and in response to this binding, resulted a cellular process