Pharmacology Lecture #2

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Drug Receptor
a macromoleculear component of a cell with which a drug interacts to produce a response (usually a protein)

Characteristics of Receptors (6)
Saturability, Reversibility, Ligand specificity, tissue specificity, stereoselectivity, transduction

Saturability
receptors exist in finite numbers

Reversibility
drug receptor interactions are dynamic and reversible

Ligand Specificity
drug-receptor interaction are specific. (shapes need to fit in pocket)

stereo-selectivity
receptors recognize specific drug isomers

4 types of Cell Surface Receptors
GPCR, Enzyme Linked receptors, Ion Channels, Transports

2 Determinants of Drug-Receptor Interactions
Physicochemical: the chemical binds agh for between drug and the receptor
Steric: the shape of the drug and the interacting site on the receptor

What is an ionic bond
Outright Transfer of electrons from one atom to another
Weak
easily made and destroyed

What is a Covalent Bond
Sharing of electrons between atoms
very strong
not reversible under biological conditions

What is a H Bond?
What Elements form them?
H atom has one electron that can form an ionic or covalent bond
F,O,N

Strength of the Bond Strengths
Covalent, IOnic, Hydrogen, Hydrophobic, Dispersion (Van der Waal)

Why are drugs that bind through weak bonds to their receptors more selective than drugs which bind through very strong bonds?
they are usually need a very precise fit of the drug to the the receptor

Why use Potassium Clavulinate with an antibiotic like Augmentin?
Because it is a Beta-lactamase inhibitor. Beta lactase is what allows a bacteria to form a resistance to the antibiotic . (example of an irreversible reaction)

Ionization of drugs affects what 5 things?
solubility, absorption, distribution, metabolism, and drug receptor interactions

What is a Bronsted-Lowry acid and base
Acid donates a proton
Base accepts a proton

what does amphoteric mean?
can act as a acid or a base

Definition of Moles
Number of moles of drug per Liter

Definition of a Strong Acid and Strong Base
Strong acid: compound dissociated completely in water generating protons
Strong base: compound dissociates completely in water generation proton acceptors

What is Ka
the acid dissociation constant

What does a High Ka mean?
high Ka=weaker conjugate base

pKa indicated strength of weak acids and bases but doesn’t tell us what?
if the drug is a weak acid or base

Weak unionized acids form ________ with strong bases such as NaOH, KOH, Ca(OH)2
salts (Na,K,Ca salts)

Weak unionized bases forms _______ with strong acids like HCl, H2SO4, HNO3
Salts (hydrochloride, sulfate, nitrate salts)

What helps us determine the fraction of drug that is in its ionized or unionized form in various pH environments?
Henderson Hasselback Equation

Henderson Hasselback Equation
pH=pKa+log(base/acid)
weak acid (HA/A)
weak base (BH/B)

when pH=pKa what is the ratio of ionized to unionized
half the drug is ionized half is unionized

When will a weak acid be more ionized?
when the pH is above pKa

when will a weak base be more ionized
When the pH is below pKa

What is an amphoteric Drug?
a drug that has one acidic and one basic group on the same molecule(multiple pKa values)

what is a Polyprotic Drug?
a drug that has multiple acidic and basic groups not eh same molecule (multiple pKa value)

how many amino acids residues per alpha helix turn?
3.6

What are constitutional Isomers?
they have the exact same formulas but the groups are in different locations

what are stereoisomers and the 2 groups
there are the dame formulas and locations but they can be rotated and shifted differently.
Entaniomers and Diastereomers

Entaniomers
mirror imaged (has plane of symmetry)
all physical properties are identical and the only difference is the direction each rotated on the plane of polarized light (L isomer is used in protein synthesis)

Diastereomers
have 2 or more curial centers
2^n=number of diastereomers

conformational isomers
are a type of diasteromer and is the result of the rotation around a single bond between 2 atoms (rotational isomers)

Cis/Trans isomers
isomers in double bonds
a)type of geometric isomerism
b)different physical properties and chemical properties
c)distributed in the system differently

stereoisomers display differential :
1 response at receptors
2 uptake at active transport
3carrier systems
4 lipid and water solubilities
5 processing by metabolic enzymes
6 excretion of drugs

Isosterism
also called Bioisoteres are substituents or groups with similar physical or chemical properties that impart similar properties to a drug
change the drug by one substituent!!!!

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