P2: Receptors and Cell Signalling

Question 1

What are the 4 types of receptor?

List them in decreasing signalling speed

Answer 1

1. Ion channels (fastest)
2. G protein-coupled receptors (GCPRs)
3. Tyrosine kinase linked receptors
4. Nuclear receptors (slowest)

Question 2

What occurs during signal amplification?

Answer 2

Binding of a ligand to a receptor induces activation of intracellular second messenger signalling cascades

Question 3

Give some examples of second messengers

Answer 3

• cAMP
• cGMP
• Ca2+
• Diacylglycerol (DAG)
• Inositol triphosphate (IP3)
• Prostaglandins

Question 4

A nicotinic Acetylcholine receptor is an example of which receptor?

Answer 4

Ion channel

Question 5

How many molecules of Ach bind to stimulates excitation?

Answer 5

2 molecules of Ach bind to stimulates excitation

Question 6

Give an example of an inhibitory ion channel

Answer 6

GABAa chloride channel

Question 7

What are the 3 major families of G proteins?

Answer 7

• Gs
• Gi/o
• Gq

Question 8

How does GPCR signalling occur?

Answer 8

1. Ligand binds and activates a receptor
2. Conformational change occurs
3. The α subunit releases its bound GDP, allowing GTP to bind in its place.
4. This exchange causes the trimer to dissociate into two activated components an α subunit and a βγ complex
5. Activation is terminated through the action of Regulators of G protein signalling that catalyse the hydrolysis of bound GTP to GDP

Question 9

What are the 3 subunits for a G protein?

Answer 9

α, β and γ

Question 10

Outline the Adenylate cyclase/cAMP pathway

Gi/o and Gs

Answer 10

1. Ligand binds to receptor activating it
2. Causes GDP to be released and GTP to bind to α-subunit of G-protein
3. Binding of GTP causes increase/decreased levels of adenyl cyclase
4. ATP to cAMP reaction is initiated
5. cAMP activates protein kinase A which phosphorylates many other proteins
6. cAMP is broken down by phosphodiesterase to AMP

Question 11

Outline the Phosphatidylinositol signal pathway (Gq)

Answer 11

1. Ligand binds to receptor and GTP binds to G protein
2. This activates phospholipase C (PLC)
3. Which hydrolyses PIP2 -> DAG + IP3 (via PLC)
4. IP3 release Ca2+ stores from ER (Ca2+ activates multiple kinases including PKC)
5. DAG activates other protein kinases

Question 12

Receptor tyrosine kinases are high affinity receptors for which molecules?

Answer 12

• Peptide growth factors
• Cytokines
• Hormones

Question 13

Explain Tyrosine Kinase signalling

Answer 13

1. Ligand binds
2. Causing conformational change results in the formation of a ​dimer​.
3. This causes ATP ​􏰀​to ADP reaction resulting in phosphorylation of receptors.

Question 14

What is Tyrosine Kinase signalling predominately involved in?

Answer 14

Cell growth and differentiation

Question 15

What type of drugs and hormones can cross cell membranes?

Lipophilic or Lipophobic?

Answer 15

Lipophilic

Question 16

What are nuclear receptors?

What do they use as 2nd messengers?

Answer 16

• Ligand activated transcription factors

- Calcium ions

Question 17

List some examples of intracellular roles calcium signalling can mediate.

Answer 17

• Muscle contraction
• Neuronal transmission
• Apoptosis
• Saliva secretion

Question 18

What determines whether or not a protein is active or not

Answer 18

Gain or loss of phosphate groups

Question 19

What are ionotropic receptors also known as

Answer 19

ligand gated ion channels

used for very rapid signalling

Question 20

What do phosphorylated tyrosine kinase receptors do

Answer 20

Act as docking stations for many other signalling molecules, triggering a wide range of pathways

Question 21

What are Ryanodine receptors and how are they activated

Answer 21

1. Dihydropyridine receptors (DHPR) is a voltage gated Ca2+ channel.
2. incoming action potential triggers opening of DHPR channels and influx of Ca2+
3. increased cytosolic Ca2+ triggers opening of ryanodine receptor and release from sarcoplasmic reticulum7