L3: Measuring agonist and antagonist activity Flashcards
homeopathy?
Chose a plant that is thought to produce the same symptoms as the disease (often myth based)
Make a tincture (plant substance in ethanol)
Dilute by 100 in ethanol (1C) 1c= 100th dilution
succuss
Dilute 3. by 100 in ethanol (2C)
succuss
Keep diluting until 6C and 30C (the more dilute the more effective…apparently)
Give one drop to the patient
“However, critics often ignore
the fact that the production
of remedies involves vigorous
agitation or succussion between
dilutions. It is this succussion
that makes the difference between an inert solution an active homeopathic remedy.
homeopathic dilution best and worst case scenario?
This is showing how dilution reduces the number of molecules of the original substance in homeopathic solutions.
Starting Concentration (Tincture) = 1 × 10⁻⁶ M
This means 1 millionth of a mole per liter (very low concentration already).
After More Dilutions
1 × 10⁻⁸ M (diluted further)
1 × 10⁻¹⁰ M (even more diluted)
6C = 1 × 10⁻¹⁸ M (homeopathic dilution method)
- How Many Molecules Are Left?
At 6C dilution (1 × 10⁻¹⁸ M):
In 1 liter, there are 600,000 molecules (6 × 10⁵ molecules).
In 100 µl (1 drop), there are only 60 molecules left.
Compare this to water molecules in 100 µl → 3.3 × 10²¹ molecules of water!
This means the homeopathic solution is almost entirely just water, with a tiny chance of any original molecules remaining.
- Extreme Case – 30C Dilution (1 × 10⁻⁶⁶ M)
At 30C, the dilution is so extreme that:
There are 6 × 10⁻⁴³ molecules per liter (which is essentially zero molecules).
To get just one molecule, you would need 2 × 10⁴² liters of solution.
How big is that?
2 × 10³⁰ km³ is the size of Jupiter’s orbit around the Sun!
That means you’d have to drink a volume of water larger than the Solar System just to have a chance of getting one molecule of the original substance.
definition of drugs and natural sources?
But natural world is a good souce of drugs
Botox- bacteria
Atropine- plant
Insulin- animal
Penicillin- fungi
Drug: a chemical substance of known structure other than a naturient or essential dietary ingeditant which wen administered to a living organism produces a biological effect.
Can be: elemt (pt), small molecule, peptide, large protein (ab), olignonucleotide (rna)
Drugs often show stero specificity: one isomer more active than another
defining receptor?
A receptor has a distinct pharmacological meaning, which results from its physiological role in cell signalling that involves recognition (binding) and transduction (conformational change produced by agonists). Key aspects are;
They interact with agonists (physiologically neurotransmitters of hormones), in order to generate a physiological response
They have a drug binding site that facilitates specificity of binding
Agonist drugs brings about functional change
The drugs leave the receptor unaltered
GPCRs, ligand-gated ion channels, Intrinsic enzyme receptors & DNA binding receptors
Not all drugs work on receptors
DNA (some anticancer drugs)
Buffers (reduce stomach acid)
Enzymes (ibuprofen)
Transporters (fluoxetine)
what are drug effects dependent on + potency?
Drug effects are conc dependent:
Subthreshold conc- no efffect. Conc so low drug does not bind to receptor
Therapeutic conc: benefits exceed the risk
High conc (overdose)- side effects
Dose- not neccessarily a conc, could be two tablets every 4 hours in a 90kg man or 60 kg woman.
Potency- a potent agonist produces a strong response at low conc. Also a potent antagonist pevents a response at a low conc. Can be good or bad. E.g: potent toxin- bad.
law of mass action?
The Law of Mass Action helps explain how drugs interact with receptors in a reversible manner.
The Law of Mass Action describes how drugs bind to receptors, similar to how substrates bind to enzymes. However, there are key differences:
Irreversible vs. Reversible Binding
In enzyme-substrate reactions, the enzyme often modifies the substrate permanently (e.g., breaking it down). This is why some reactions are not reversible.
In drug-receptor interactions, most drugs do not permanently modify the receptor. The binding is usually reversible, meaning the drug can detach and the receptor returns to its original state.
Receptor Can Change Shape
Some receptors have catalytic activity, but not in response to drug binding.
A receptor can change shape upon binding, but the drug remains attached (this is called conformational change).
Two-State Model
The receptor exists in two states:
Inactive state (R) → Not triggering a response.
Active state (R)* → Produces a response when bound by a drug.
Some drugs may bind and *not activate the receptor (R)**, while others can activate it.
Reversibility in Drug Action
Unlike enzyme-substrate reactions, the drug-receptor equation is reversible:
D + R ↔ DR ↔ DR*
chat: The Two-State Model of receptor activation describes how receptors exist in two conformations:
Inactive state (R) – The receptor is not signaling.
Active state (R)* – The receptor is in a shape that allows it to signal.
Since the receptor isn’t permanently changed, it can return to its resting state and continue functioning after the drug detaches.
drug (D) binding?
important graphs
saturation is easily measured ie. maximum number of binding sites (BmaxO. but difficult to get a measure of how avidly the drug binds - affinity (KD)
To measure non-specific binding, you typically use a radioligand binding assay and include an excess of an antagonist to block the specific binding sites.
maths?
D + R ↔ DR
so this means: XD + (Bmax-B) ↔ (forward arrow K+1_ backwards K-1) B
so
XD(B max −B)K +1 =K −1 B
and B/Bmax= xd/ xd + (k/-1/k+1)
𝑋𝐷 = concentration of the free drug
𝐵𝑚𝑎𝑥= total number of receptors
B = number of bound receptors
𝐾+1 = rate constant for drug binding
𝐾−1= rate constant for drug unbinding
equillbirum dissociation constant: KD = k-1/k+1
Since at equilibrium, the number of drugs binding per second equals the number of drugs unbinding, we can rearrange this into a useful equation:
B = BMAX XD/ KD+ XD
this can be linearised to y=mx + c form
B/XD= BMAX/KD-B/KD
scratchard plot?
B/XD= BMAX/KD-B/KD
bound drug (B) x axis and bound drug/free drug (B/XD) Y AXIS
often free drug does not significantly change unless small volume
downward slope
slope= -1/KD
bmax at x intercept
why is pharmacology not homeopathy?
This is why pharmacology is not homeopathy the KD is a physiochemical constant like Avogadro’s number
The KD is the same for a given receptor and drug combination in any tissue, in any species, anywhere in the universe
The KD can therefore be used to identify an unknown receptor
