What do most drugs act on?
Protein targets such as receptors, ion channels, enzymes, and carrier molecules (transporters).
How do drugs interact with protein targets?
They bind to specific binding sites on the protein.
Name an example of a drug that does not act on a protein target.
Colchicine, which binds to tubulin to prevent neutrophil migration in gout, causing a ‘drunken walk’ effect.
What are receptors?
Proteins involved in chemical communication that coordinate the function of cells by binding hormones, neurotransmitters, or growth factors.
What are the two main types of receptor-acting drugs?
Agonists (activate receptors) and antagonists (prevent activation).
Define a ligand.
Any molecule (agonist or antagonist) that binds to a receptor.
Give an example of a receptor-drug interaction.
Noradrenaline activates β-adrenoreceptors in the heart (agonist), increasing heart rate; propranolol blocks them (antagonist), reducing cardiac contraction.
What are ligand-gated ion channels?
Ion channels that open only when occupied by an agonist molecule.
What are voltage-gated ion channels?
Channels that open in response to changes in membrane voltage.
Give an example of a drug that affects ion channels.
Lidocaine blocks voltage-gated sodium channels to reduce neuron firing (local anaesthetic).
How do benzodiazepines act on ion channels?
They bind to GABA receptor/chloride channel complexes, facilitating opening by GABA to increase inhibition.
How do drugs act on enzymes?
They often act as substrate analogues to competitively inhibit the enzyme or as false substrates that alter normal metabolic pathways.
Give an example of an enzyme-inhibiting drug.
Aspirin inhibits the enzyme cyclooxygenase.
What is a false substrate?
A drug that is transformed into an abnormal product, disrupting normal metabolism.
Give an example of a false substrate drug.
Fluorouracil replaces uracil in nucleotide synthesis, blocking thymidylate production and preventing DNA synthesis.
What are pro-drugs?
Inactive forms of drugs that require enzymatic conversion into active forms.
What are transporters (carrier molecules)?
Membrane proteins that transport ions and small molecules like glucose across membranes.
How can drugs affect transporters?
They can act as inhibitors or false substrates.
Give examples of drugs that inhibit transporters.
Tricyclic antidepressants and cocaine inhibit noradrenaline reuptake, increasing NA availability at receptors.
How do amphetamines act as false substrates?
They compete with noradrenaline for transport into nerve terminals, increasing synaptic NA levels.
What are the effects of amphetamine-like drugs?
They cause locomotor stimulation, euphoria, increased blood pressure, followed by fatigue, depression, and anxiety upon withdrawal.
What is a toxicant?
Any harmful substance.
What is a toxin?
A naturally produced toxicant.
What are the main targets for toxins and toxicants?
Proteins, lipids, and nucleic acids (DNA).
