Chapter 14
Chapter 14: Signal Transduction Mechanisms: Messengers and Receptors
Signal Transduction Mechanisms: II. Messengers and Receptors
In the second major means of intercellular communication the signal is transmitted by regulatory chemical messengers
Receptors are located on receiving cells that can be quite distant from the secreting cell
Chemical Signals and Cellular Receptors
Cells produce signals, in some cases by displaying molecules on their surfaces or by releasing a chemical signal
Multicellular organisms can control the activities of specialized cells through release of chemical messengers
Affinity: the relationship between concentration of ligand and # of receptors occupied
High- most receptors occupied at low [ligand]
Low- need high [ligand] for most receptors to be occupied
Dissociation constant- Kd: concentration of free ligand needed to produce a state in which half the receptors are occupied
Low Kd- high affinity receptors
High Kd- low affinity
Binding Affinity
The free energy of interaction between a protein (P) and it ligand (L) can vary greatly
Some affinities for ligands can be so high that dissociation can never occur
Binding affinity is measured by the association constant for the binding equilibrium (Keq) or dissociation constant (Kd)
L + P (2 way arrow) LP
Keq=[LP]/[L][P] Kd=[L][P]/[LP] High Kew or Low Kd= high affinity
Synthetic Ligands – Drugs
Agonists – bind and activate receptors
- Isoproterenol activates B-adrenergic receptors
Antagonists- bind to receptors without triggering a change
- They prevent the naturally occurring messenger from activating the receptor
- Propanolol inhibits B-adrenergic receptors
- Damotidine (Pepcid AC) binds and inhibits a histamine receptor in stomach cells
look at diagrams 13-15
Messengers
First (primary) messengers Ligands that bind the receptor
- Hydrophilic ligands bind extracellular receptors
- Hydrophobic ligands bind intracellular receptors
- Examples: proteins (insulin, peptides
Signal Transduction Mechanisms: II. Messengers and Receptors
In the second major means of intercellular communication the signal is transmitted by regulatory chemical messengers
Receptors are located on receiving cells that can be quite distant from the secreting cell
Chemical Signals and Cellular Receptors
Cells produce signals, in some cases by displaying molecules on their surfaces or by releasing a chemical signal
Multicellular organisms can control the activities of specialized cells through release of chemical messengers
Affinity: the relationship between concentration of ligand and # of receptors occupied
High- most receptors occupied at low [ligand]
Low- need high [ligand] for most receptors to be occupied
Dissociation constant- Kd: concentration of free ligand needed to produce a state in which half the receptors are occupied
Low Kd- high affinity receptors
High Kd- low affinity
Binding Affinity
The free energy of interaction between a protein (P) and it ligand (L) can vary greatly
Some affinities for ligands can be so high that dissociation can never occur
Binding affinity is measured by the association constant for the binding equilibrium (Keq) or dissociation constant (Kd)
L + P (2 way arrow) LP
Keq=[LP]/[L][P] Kd=[L][P]/[LP] High Kew or Low Kd= high affinity
Synthetic Ligands – Drugs
Agonists – bind and activate receptors
- Isoproterenol activates B-adrenergic receptors
Antagonists- bind to receptors without triggering a change
- They prevent the naturally occurring messenger from activating the receptor
- Propanolol inhibits B-adrenergic receptors
- Damotidine (Pepcid AC) binds and inhibits a histamine receptor in stomach cells
look at diagrams 13-15
Messengers
First (primary) messengers Ligands that bind the receptor
- Hydrophilic ligands bind extracellular receptors
- Hydrophobic ligands bind intracellular receptors
- Examples: proteins (insulin, peptides