Cell Communication Wk2

Question 1

What are the three main types of cell signalling?

Answer 1

• Endocrine signalling
• Paracrine signalling
• Autocrine signalling

Question 2

What type of transmission does most synapses have?

Answer 2

Chemical (electrical)

Question 3

Describe the process of first messengers

Answer 3

• First messenger allows communication
• Binds to receptor on surface of the cell
• Second message is stimulated to be produced - which is responsible for producing signals

Question 4

What are the milestones in receptor biology?

Answer 4

• 1921 - Vagusstoff (Otto Loewi experiment)
• 1936 - Acetylcholine as neurotransmitter (Sir Henry Dale)
• 1957 - cAMP (Earl Sutherland and Ted All)
• 1962 - Adenylyl Cyclase (Earl Sutherland and Ted Rall)
• 1968 - Protein kinase A (krebs and Fischer)
• 1970 - Isolation of nicotinic MACh receptor (J-P Changeux et al.)
• 1970s - Radioligand binding assays
• 1976 - Cloning of Beta-adrenergic receptor (R. Lefkowitz)
• 1980 - G proteins (Alfred G. Gilman and Martin Rodell)
• 2000-today - GPCR structures

Question 5

What was the Otto Loewi experiment?

Answer 5

To experiment and see whether it was electrical or required a neurotransmitter.
Using 2 hearts, they were slowed down with the use of a stimulus - this showed transmission of neurotransmitters.

Question 6

What is the timeline for the isolation of ACh?

Answer 6

• 1914 - Isolation of acetylcholine from ergot
• 1929 - Isolation of MACh from human body (prompted by Loewi experiment)
• 1933-1936 - Proof of Ash as a neurotransmitter

Question 7

What are the nicotinic effects of AChRs?

Answer 7

• Agonist - Nicotine
• Antagonist - curare
• Muscle contraction
• Synaptic transmission (autonomic ganglia, parasympathetic postganglionic, CNS)
• nAChRs (ion channels)
• Can block effectiveness of acetylcholine

Question 8

What are the muscarinic effects of AChRs?

Answer 8

• Antagonist - Atropa Belladonna alkaloids (atropine, scopolamine etc.)
• Bradycardia, salivation, bronchospasm, midriasis
• M1-5 (GPCRs)

Question 9

How does the nicotinic AChRs controlled?

Answer 9

• Absence of Ash means that the gates are closed
• When hydrophobic interactions break, the ‘gate opens’
• Conformational change is what occurs

Question 10

How are biological effects measured?

Answer 10

• Radiological and binding assay -
  1. Receptor contained in sample
  2. Add radioactive ligand (they will bind)
  3. Wash
  4. Measure radioactivity
• Can also record trace of movement of tissue (e.g. an ECG)

Question 11

How do ligands and receptors interact?

Answer 11

• Biomolecular interactions:
  kon
  R + L RL
  koff
• Binding is not all or nothing
• Portion of R and L will be bound but some will be free
• d[RL]/dt = K(on)[R][L] - K(off)[RL] — Mass action law
• Equilibrium is released when K(on)[R][L] = K(off)[RL]
• Rearranging –> Dissociation constant (Kd) - 50% of receptors occupied, measure of affinity) –>
  Kd = K(off)/K(on) = [R][L]/[RL]

Question 12

What is fraction of occupancy?

Answer 12

[RL]/[R]total = L/[L]+Kd