Receptors 1

Question 1

What are the two types of intercellular signalling?

Answer 1

1. Signalling by secreted molecules

2. Signalling by plasma membrane- bound molecules

Question 2

What are the 3 types of Signalling by secreted molecules?

Answer 2

1. Paracrine
2. Endocrine
3. Synaptic

Question 3

Describe paracrine signalling

Answer 3

•If a signalling molecule is secreted into a tissue and acts on adjacent cells - signalling molecule is called a local mediator

Question 4

When is it endocrine signalling?

Answer 4

If the signalling molecules are released into the bloodstream and travel through the blood to the target cell. Signalling molecule is termed a hormone

Question 5

When is it synaptic signalling?

Answer 5

If nerve cells release a neurotransmitter into a junction between nerve cells, then the signalling molecule is called a neurotransmitter.

Question 6

What are the 3 subdivisions of signalling molecules?

Answer 6

1. Local chemical mediators
2. Hormones
3. neurotransmitters

Question 7

What are the two types of receptors regarding location?

Answer 7

Cell surface receptors Intracellular receptors

Question 8

When are cell surface receptors used?

Answer 8

When the signalling molecule is hydrophilic so can’t pass the lipid bilayer

Question 9

When are the receptors intracellular?

Answer 9

When the signalling molecule is hydrophobic so can pass through the lipid bilayer into the cell. Eg steroid hormones, thyroid hormones, oestrogen

Question 10

What is a receptor

Answer 10

A receptor is a molecule that recognises specifically a
second molecule (ligand) or family of molecules and
which in response to ligand binding brings about
regulation of a cellular process

Question 11

What is a ligand?

Answer 11

A ligand is any molecule that binds specifically to a

receptor site

Question 12

When is a ligand termed as an agonist?

Answer 12

When a ligand produces activation of a receptor

Question 13

When is a ligand termed an antagonist?

Answer 13

When a ligand combines with a receptor site
without causing activation.

It opposes the actions of an agonist

Question 14

What is the role of receptor in cellular physiology?

Answer 14

• Signalling by hormones/local chemical mediators
• Neurotransmission
• Cellular delivery
• Control of gene expression
• Cell adhesion
• Modulation of the immune response
• Sorting of intracellular proteins
• Release of intracellular calcium stores

Question 15

What is know about Binding affinity at receptor binding sites?

Answer 15

Affinity of ligand binding at receptor sites is generally
much higher than binding of substrates and allosteric
regulators to enzyme sites

Question 16

What are receptors classified according to?

Answer 16

Specific physiological signalling molecule (agonist) recognised

Question 17

What is the sb classification of receptors?

Answer 17

Affinity (tightness of binding) of a series of antagonists

Question 18

What are the two receptor types of acetylcholine receptors?

Answer 18

Nicotinic Acetylcholine receptor

Muscarinic acetylcholine receptor

Question 19

What is the agonist for nicotinic acetylcholine receptors?

Answer 19

Nicotine

Question 20

What is the agonist for muscarinic acteylcholine receptor?

Answer 20

Muscarine

Question 21

How do you distinguish between a receptor and acceptor?

Answer 21

Receptor

• Silent at rest Agonist
• binding stimulates a biological response

Acceptor

• Operate in absence of ligand
• Ligand binding alone produces no response

Question 22

Which are the 4 types of receptors which transduce extracellular into intracellular signals?

Answer 22

1. Membrane-bound receptors with integral ion channels
2. Membrane-bound receptors with integral enzyme activity
3. Membrane-bound receptors which couple to effectors through transducing proteins
4. Intracellular receptors

Question 23

Describe how a Membrane-bound receptors with integral ion channels works?

Answer 23

An agonist binding causes an ion channel to open for a particular ion which results in changes in cellular activity.
E.g. nicotinic acetylcholine receptors

Question 24

Describe how Membrane-bound receptors with integral enzyme activity work?

Answer 24

Transmembrane protein such that when the agonist binds to the receptor site on the outside, a conformational change occurs which activates it and an enzyme converts a molecule into a second messenger which can carry the signal on

Question 25

What is the advantage of Membrane-bound receptors which couple to effectors through transducing proteins?

Answer 25

Possibility of plasticity as different receptors that recognise the same transducer can be connected to the effector

Question 26

How do Intracellular receptors work?

Answer 26

* Hydrophobic signals enter the cell through the bilayer * These receptors bind to transcription factors and modify gene expression. * Rare

Question 27

Give 4 examples of Membrane-bound receptors with integral ion channels which belong to the classical receptor family and their ion selectivity

Answer 27

1. Nicotinic acetylcholine receptor (nAChR) - gated Na+, K+ and Ca2+ channel 2. Gamma amino butyric acid (GABA) receptor - gated chloride (Cl-) channel 3. Glycine receptor - gated chloride (Cl-) channel 4. Glutamate receptors (NMDA, kainate and AMPA) - gated entry of Ca2+

Question 28

Give 3 examples of non classical ligand gated ion channels

Answer 28

1. ATP sensitive K+ channel 2. P2x purinoceptor (Na+/Ca2+) 3. Ryanodine receptor (Ca2+)

Question 29

Give two examples of Membrane-bound receptors with integral enzyme activity

Answer 29

1. Atrial natriuretic peptide (ANP) receptor - linked directly to guanylyl cyclase - GTP -> cGMP 2. Growth factor receptors (Insulin, epidermal growth factor (EGF), platelet-derived growth factor (PDGF)) - linked directly to tyrosine kinase

Question 30

Describe the process of tyrosine kinase-linked receptors

Answer 30

1. AUTOPHOSPHORYLATION - insulin binds to the receptor triggering the. Phosphorylation of the receptor 2. Enzyme activation - enzyme binds to phosphotyrosine recognition site which activates enzyme OR 1. TRANSDUCER ACTIVATION - transducer binds to tyrosine - phosphatase receptor. Activated 2. ENZYME ACTIVATION -enzyme binds to transducer and becomes activated. Remember activated = phosphorylated (in this case )

Question 31

What are there so many phosphorylation sites within transducers in tyrosine kinase linked receptor mechanism?

Answer 31

``` Insulin has many function: Stimulates glucose storage Inhibition of glycogen breakdown Fat storage Inhibition of Lipolysis ``` So different signals for many different functions so needs to set off many different regulatory pathways. Each phosphorylation site within transducer are the docking points for each pathway.

Question 32

Describe the structure of G protein coupled receptors

Answer 32

* Binding domains are within the plane of the membrane * The g protein coupling domain is intracellular * Seven transmembrane domains fold to form a cleft into which the ligand binds

Question 33

Describe the intracellular receptor family

Answer 33

* Receptor held in silent state because of inhibitory protein blocking the DNA binding site * On binding of hormone, the receptors change conformation so that the inhibitory protein is released and the DNA binding site is exposed

Question 34

Describe Amplification in cellular signalling

Answer 34

* One ligand binding to a receptor can activate multiple G proteins until the ligand dissociates because after a G protein leaves the activated receptor another can bind * Each G protein can activate many enzymes e.g adenlyl cyclase which converts ATP to cAMP which activates protein kinase A * Each protein kinase A can phosphorylate multiple enzymes * Each of the enzymes can produce thousands of products * Thus amplification occurs at any steps

Question 34

Are responses to receptors activation or inhibition?

Answer 34

Responses to receptor activation can lead to cellular activation or inhibition depending on the receptor activated