Biological signalling molecules

Question 1

Compare osmolarity and osmolality

Answer 1

Units of measurement

Osmolarity = osmoles of solute in 1L solution
Concentration of an osmotic solution

Osmolality = osmoles of solute in 1kg solvent

Question 2

Define receptor

Answer 2

A molecule that recognises specifically, a second molecule (ligand) or family of molecules.
In response to ligand binding brings about regulation of a cellular process.

Question 3

What is a ligand?

Answer 3

Any molecule that binds specifically to a receptor site

Question 4

Describe agonists and antagonists

Answer 4

AGONIST:
Ligand binding ACTIVATES receptor

ANTAGONIST:
Ligand binding blocks site, preventing action of agonist.

Question 5

What are the roles of receptors in cellular physiology?

Answer 5

1. Signalling
2. Neurotransmission
3. Cellular delivery
4. Gene expression control
5. Cell adhesion
6. Modulation of immune response
7. Sorting intracellular proteins
8. Release intracellular Ca2+ stores

Question 6

Compare ligand binding affinity at receptor sites with substrate / allosteric regulators to enzyme sites

Answer 6

Affinity = tightness of binding into site.

Ligand binding to receptor sites higher affinity than enzyme / substrate.

Receptor binding range nano-micromolar
Enzyme micro-millimolar.

Question 7

How are receptors classified

Answer 7

1. Agonist recognised
2. Affinity of series of antagonists

e.g., Nicotinic Acetylcholine Receptors

Question 8

Acetylcholine receptors are either…

Answer 8

• Nicotinic

- Muscarinic

Question 9

What are the 4 methods of signal transduction?

Answer 9

1. Membrane-bound receptors with ion channels
2. Membrane-bound receptors with enzyme activity
3. Membrane-bound receptors which couple to effectors (through transducing proteins)
4. Intracellular receptors

Question 10

Name 4 membrane-bound receptors with integral ion channels.

Answer 10

1. nAChR (Nicotinic Acetylcholine receptor
   - gated Na+, K= and Ca2+ channel
2. GABA (Gamma amino butyric acid receptor
   - gated Cl- channel
3. Glycine receptor
   - gated Cl- channel
4. Glutamate receptors (NMDS, AMPA, kainate)
   - Gated Ca2+ ENTRY

Question 11

Name 2 membrane-bound receptors with integral enzyme activity

Answer 11

1. ANP receptor (Atrial natiuretic peptide)
   - Linked directly to guanylyl cyclase
   - GTP > cGMP
2. GROWTH FACTOR receptors
   - Insulin
   - EGF (Epidermal growth factor)
   - PDGF (Platelet-derived growth factor)

• Linked directly to tyrosine kinase

Question 12

State the effect of noradrenaline and acetylcholine on cardiac pacemaker cells.

Answer 12

NORADRENALINE:
> beta1 adrenoceptors > increased heart rate

ACETYLCHOLINE:
> M2 muscarinic receptors > slows heart rate

Question 13

State the effect of insulin and glucagon on hepatocytes

Answer 13

INSULIN:
> Stimulates glycogen synthesis from glucose

GLUCAGON:
> Stimulates glycogen breakdown to glucose