AAs and Buffers Flashcards
midterm 1
what is an amino acid?
a compound consisting of a central carbon atom, attached to an amino group, a carboxyl group, a side chain (R group), and an H atom
oligopeptide
few amino acids joined together
polypeptide
many amino acids joined together ( 4 or more)
Protein
a macromolecule that consists of one or more polypeptide chains (50 AA’s or greater)
how many common AA’s are there?
20
what are all proteins composed of?
20 “standard” AA’s, which are those for which at least one codon exists in the genetic code
what are common AA’s known as?
alpha amino acids
4 classifications of AA’s based off R groups
- Non-polar (hydrophobic)
- Polar neutral (unionized)
- Polar negatively charged (acidic)
- Polar positively charged (basic)
unique AA’s
Glycine: has two H groups
Proline: has a secondary amino group (rather than a primary amino group)
what is an essential amino acid?
an amino acid that must be obtained through diet; can’t be synthesized from other precursors (ex. Histidine)
AA configuration
alpha carbon ( a chiral center)
D or L configuration (all biological proteins are L-stereoisomers)
Electrolytes
are substances that dissociate in water into a cation (+ charged ion) and anion (- charged ion)
types of electrolytes
strong electrolytes: completely dissociate in solution (ex. strong acids/bases, salts)
weak electrolytes: partially dissociate in solution (ex. weak acid/bases)
non-electrolytes: dissolve as molecules in solution (ex. sugars/alcohols)
Bronsted-Lowry theory
acids: compounds that donate protons (H+)
bases: compounds that accept protons (H+)
Lewis theory
acids: electron pair acceptors
bases: electron pair donors
pH equation
pH= -log [H+]
Keq/Ka equation and purpose
Keq (Ka)= [H+][A-]/[HA]
measure strength of an acid
Ka and H+ relationship
larger Ka= greater # of H+ ions released, which means a stronger acid
what is the Ka constant?
acid dissociation constant
pKa equation
pKa= -logKa
pKa and H+ relationship
lower pKa= greater # of H+ ions released, which means a stronger acid
pKa difference from pH
pH is conc. dependent, pKa is constant for each type of molecule
Henderson-Hasselbalch equation
pH=pKa + log [A-]/[HA]
[A-]= conj. base
[HA]= weak acid
Henderson-Hasselbalch purpose
used to to tell if [A-] or [HA] is dominant
allows us to predict the relative amounts of protonated vs unprotonated species in a solution
AA’s at physiologic pH
amino group is protonated
carboxylic acid group is unprotonated
due to the pKa of the side groups
How are AA’s amphoteric molecules?
carboxyl groups= weakly acidic
amino groups= weakly basic
r groups= ionizable
Zwitterion molecules
molecules which bear plus & minus charges simultaneously (diploar ions)
when are AA’s Zwitterions?
at physiological pH
Buffers
are solutions which resist a change in pH when acids or bases are added
is a mixture of either HA/A- or HB+/B
example of how a buffer works
if acid is added, A- can neutralize
(->HA)
if base is added, HA can neutralize (-> A-)
maximal buffering capacity occurs…
when pH=pKa (can buffer effectively within +/- 1 ph=pKa difference
Henderson-Hasselbalch equation for Buffers
if pH of the solution is less than pKa of the buffer, [HA]>[A-] (solution is mostly protonated)
if pH of the solution is more than pKa of the buffer, [HA]<[A-] (solution is mostly unprotonated)
MOA of Pilocaprine HCl opthalamic solution
primary MOA: pupil constriction
secondary MOA: ciliary muscle contracts
Pilocarpine
-unstable at physiologic pH
-stored at pH=4, pKa=6.6, so pH<pKa
- will exist in the protonated form (less absorption)
Drug absorption
- oral drugs must cross stomach/intestinal epithelium for absorption into the blood (uncharged form)
- so best absorbed at pH which results in neutral molecule (HA or B)
Renal system relationship to drug excretion
-weakly acidic/basic drugs are filtered at the glomeruli for excretion
-urine pH determines the amount of drug excretion/retention
urine pH
alkaline urine= weakly acidic drugs excreted more rapidly
acidic urine= weakly basic drugs excreted more rapidly
