lecture 4

Question 1

describe ligand gated ion channels

Answer 1

• Chemical signal binds to receptor protein
• Binding causes opening of a pore in the protein, allows flow of ions
  
  • Important in nerve transduction
    -Millisecond
• E.g. Nicotinic

Question 2

describe G protein coupled receptors

Answer 2

• Ligand binds to receptor, which binds to G protein
  
  • Can be stimulating or inhibitory
  • G protein binds to another protein, usually a enzyme or membrane protein
  • Remains activated for a short time
  • Seconds
• E.g. muscarinic

Question 3

describe kinase linked receptors

Answer 3

• Large + heterogeneous group of membrane receptors
  
  • Response to protein mediators
  • Binding of ligand forms dimers, which activate tyrosine kinase activity
• Tyrosine kinase accepts a high-energy phosphate from ATP + transfers this activates a protein
  
  • Initiates transduction
  • Hours
  • Cytokine receptors

Question 4

describe nuclear receptors

Answer 4

• Receptors that regulate gene transcription
• To stimulate intracellular receptors, the chemical stimuli must be able to cross the cell membrane
  
  • Most chemical stimuli protein, so cant cross
  • Those that can include steroid class hormones
  • Hours
• Oestrogen

Question 5

describe the signal transduction pathways

Answer 5

Series of reactions that pass the info from the receptor to lead to the cellular response
- Is long and complex, because
- Amplifies the signal
- Each step activates more molecules, which activate more
- Specific
Some signals bind to multiple cells and produce different responses

Question 6

what are secondary messengers

Answer 6

• Small, water soluble molecules/ions
• Carry signal transduction message from the receptor (1st message) to the next site of cell response

Question 7

describe cAMP as a secondary messenger

Answer 7

○ cAMP activated when
§ Agonist binds to receptor
§ Change in receptor conformation
○ Activates G-protein complex, which activates adenylyl cyclase
○ This converts ATP into cAMP
○ cAMP activates protein kinase A
Protein kinase A then sets off a cascade of protein phosphorylation leading to the cell response

Question 8

describe calcium as a secondary messenger

Answer 8

○ Increasing intracellular Ca2+ conc. Can lead to cellular responses
○ Increase in intracellular Ca2+
§ May directly affect target proteins
May act indirectly by binding to calmodulin (smooth muscle contraction)

Question 9

describe the cascade process

Answer 9

1. Signal molecule binds to G protein coupled receptor (GPCR) which activates the G protein
   
   2. G protein turns on adenylyl cyclase, an amplifier enzyme
   3. Adenylyl cyclase converts ATP to cyclic AMP
   4. cAMP activates protein kinase A
   5. Protein kinase A phosphorylates other proteins, leading ultimately to a cellular response

Question 10

describe adrenaline as a secondary messenger

Answer 10

different process to intracellular cascade
but when binds to a receptor on blood vessels, can make it constrict or dilate

* Alpha 1
	○ Leads to smooth muscle contraction
	
* Alpha 2
	○ Inhibition of transmitter release
	○ Smooth muscle contraction

* Beta
	○ Heart muscle contraction
	○ Smooth muscle relaxation glycogenolysis