Signalling between cells II

Question 1

What are the types of receptor used for intracellular signalling? Give brief outline on how they work

Answer 1

Ionotropic - ligand binding - ion channel opened

G-Protein - lkigand binding - activates internal G protein

Enzyme-linked - ligand binds - receptor clusters - internal enzyme activated

Intracellular - membrane permeable ligand binds to receptor in cell

Question 2

Outline signal transduction in ionotropic receptors

Answer 2

1. Ligand binds to receptor protein
2. Conformational change in channel protein - pore opens
3. Pore allows ions to move

Question 3

Give examples of ionotropic receptors and the ligands involved

Answer 3

Nicotinic acetylcholine
- ACh, for contraction

GABA
- GABA, for neuronal relaxation

Question 4

Outline signal transduction in G-protein receptors

Answer 4

1. 7-TM receptor and G protein inactive
2. Ligand binds - conformational change
3. G-protein binds to receptor, GDP phosphorylated
4. G-protein disassociates into alpha and betagamma, binding to target proteins
5. Internal GTPase dephosphorylates GTP on alpha unit
6. Alpha unit dissociates from target protein, inactive again
7. Receptor active until ligand leaves

Question 5

Give examples of G-protein receptors and the ligands involved

Answer 5

Gs

• Stimulates adenylyl cyclase
• ATP conv to cAMP which activates PKA, incr HR

Gi

• Inhibits adenylyl cyclase
• Reduces levels of PKA, decr HR -muscarinic receptor

Gg

• Stimulates Phospholipase C
• Vasoconstriction

Question 6

Outline signal transduction in enzyme-linked receptors

Answer 6

1. Ligand binds, causes receptors to cluster
2. This causes enzymes to be activated in cytoplasmic domain, which then phosphorylate receptor
3. Phosphorylation leads to signal proteins binding to cyt domain of receptor
4. These signalling proteins recruit others, generating signal

Question 7

Give examples of enzyme-linked receptors and the ligands involved

Answer 7

Tyrosine kinase

• Insulin receptor - insulin
• ErbB receptor - epidermal growth factor

Guanylyl cyclase

• NPRA - atrial - brain natriuretic peptide
• • • vasodilation

Question 8

Outline signal transduction in intracellular receptors

Answer 8

Type 1 - cytoplasmic

• Hormone binds to receptor after being chaperoned
• Chaperone molecule pisses off, dimer forms between receptor and hormone
• Homodimer translocates to nucleus and binds to DNA

Type 2 - nuclear
- Binding of hormone ligand - transcription regn

Question 9

Give examples of intracellular receptors and the ligands involved

Answer 9

Type 1

• Glucocorticoid receptor
  
  • Cortisol, increases gluconeogenesis

Type 2

• Thyroid hormone receptor
  
  • Thyroxine, T3, growth and dev