Receptors and signalling

Question 1

what is a ligand?

Answer 1

A ligand is any molecule that binds to a receptor

Question 2

what is an endogenous agonist?

Answer 2

A chemical mediator found in the body that bind to receptors to produce a response

Question 3

what is an example of an endogenous agonist?

Answer 3

acetylcholine, insulin or noradrenaline

Question 4

what is divergence signalling?

Answer 4

A single signal can activate multiple pathways, leading to diverse cellular outcomes.
ONE INPUT, MULTUPLE OUTPUT.

Question 5

what is convergence signalling?

Answer 5

multiple receptors on one cell ultimately converge to activate a response or pathway. MULTIPLE INPUT, ONE OUTPUT
This allows amplification where multiple signals converge onto aa common downstream effector leading to a stronger response.

Question 6

what is a receptor?

Answer 6

they are macromolecular proteins. They are recognition sites for different chemical mediators
AND
proteins of a cell that bind a molecule which modulates some activity of the cell

Question 7

what are the four receptor classes?

Answer 7

ligand ion gated channel
G protein -coupled receptor
kinase-linked receptor
nuclear receptor

Question 8

Why is Nuclear receptors also called
1. Cytoplasmic receptors
2. Intracellular receptors

Answer 8

1. Because, rather than floating in the nucleus, it could be in the cytoplasm of the cell.
2. Because it’s found in the cell rather than on the membrane.

Question 9

Which chemical mediators use each receptor type?

Answer 9

(–>) = activated by

Nucelar receptors –> steroidal hormones

Kinase linked receptros –> Peptide hormones, cytokines

G protein coupled receptors –> Peptide hormones + most small molecule chemical mediators e.g. amino acid derived neurotransmitters

Ligand gated ion channel receptors –> most small molecule chemical mediators e.g. amino acid derived neurotransmitters

Question 10

what type of mediators use ligand gated ion channels?

Answer 10

small molecule chemical mediators such as amino acid derived neurotransmitters

Question 11

what type of mediators use g protein coupled receptors?

Answer 11

Proteins and small molecules chemical mediators such as amino acid derived neurotransmitters

Question 12

what type of mediators use g protein coupled receptors?

Answer 12

Proteins and small molecules chemical mediators such as amino acid derived neurotransmitters

Question 13

what type of mediator uses nuclear receptors?

Answer 13

steroid hormones such as oestrogen

Question 14

what is signal transduction?

Answer 14

The process that turns extracellular signals into intracellular signals

Question 15

What does nAChR stand for?

Answer 15

Nicotinic Acetylcholine Receptor

(It’s an excitatory ligand gated ion channel)

Question 16

What are the properties of cell surface Receptors?

Answer 16

(Ionotropic / metabotropic / kinase linked)

• each has transmembrane spanning segments
• each possesses a ligand binding domain (usually extracellular)
• ligands are hydrophilic, i.e. they can not cross the cell membrane

Question 17

Why are G protein coupled receptors called “metabotropic”?

Answer 17

It can influence a signalling cascade (metabolic reactions associating phosphates, etc) within the cell

Question 18

Key ideas about G protein coupled receptors (GPCRs)?

Answer 18

Formed from a single transmembrane protein

Receptor protein spans the membrane 7 times (so 7 transmembrane domains TMD)

Its has 3 different sub units
–> alpha
–> beta
–> gamma
So its a heterotrimetric GTP-binding protein (G protein)

Question 19

Key ideas about ligand gated ion channels?

Answer 19

Involve ion channels

Involved in Fast synaptic transmission

Endogenous agonists are fast classical neurotransmitters stored in synaptic vesicles

Composed of 3-5 subunits i.e. transmembrane proteins

Complex arranged to form central aqueous pore

Agonist binding –> causing channel to open

Channel closes when agonist is removed OR receptor enters a “desensitised” state

Question 20

What are the 2 types of ligand gated ion channel receptors?

Answer 20

Excitatory

Inhibitory