AAs and Buffers

Question 1

what is an amino acid?

Answer 1

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

Question 2

oligopeptide

Answer 2

few amino acids joined together

Question 3

polypeptide

Answer 3

many amino acids joined together ( 4 or more)

Question 4

Protein

Answer 4

a macromolecule that consists of one or more polypeptide chains (50 AA’s or greater)

Question 5

how many common AA’s are there?

Answer 5

20

Question 6

what are all proteins composed of?

Answer 6

20 “standard” AA’s, which are those for which at least one codon exists in the genetic code

Question 7

what are common AA’s known as?

Answer 7

alpha amino acids

Question 8

4 classifications of AA’s based off R groups

Answer 8

1. Non-polar (hydrophobic)
2. Polar neutral (unionized)
3. Polar negatively charged (acidic)
4. Polar positively charged (basic)

Question 9

unique AA’s

Answer 9

Glycine: has two H groups
Proline: has a secondary amino group (rather than a primary amino group)

Question 10

what is an essential amino acid?

Answer 10

an amino acid that must be obtained through diet; can’t be synthesized from other precursors (ex. Histidine)

Question 11

AA configuration

Answer 11

alpha carbon ( a chiral center)
D or L configuration (all biological proteins are L-stereoisomers)

Question 12

Electrolytes

Answer 12

are substances that dissociate in water into a cation (+ charged ion) and anion (- charged ion)

Question 13

types of electrolytes

Answer 13

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)

Question 14

Bronsted-Lowry theory

Answer 14

acids: compounds that donate protons (H+)
bases: compounds that accept protons (H+)

Question 15

Lewis theory

Answer 15

acids: electron pair acceptors
bases: electron pair donors

Question 16

pH equation

Answer 16

pH= -log [H+]

Question 17

Keq/Ka equation and purpose

Answer 17

Keq (Ka)= [H+][A-]/[HA]
measure strength of an acid

Question 18

Ka and H+ relationship

Answer 18

larger Ka= greater # of H+ ions released, which means a stronger acid

Question 19

what is the Ka constant?

Answer 19

acid dissociation constant

Question 20

pKa equation

Answer 20

pKa= -logKa

Question 21

pKa and H+ relationship

Answer 21

lower pKa= greater # of H+ ions released, which means a stronger acid

Question 22

pKa difference from pH

Answer 22

pH is conc. dependent, pKa is constant for each type of molecule

Question 23

Henderson-Hasselbalch equation

Answer 23

pH=pKa + log [A-]/[HA]
[A-]= conj. base
[HA]= weak acid

Question 24

Henderson-Hasselbalch purpose

Answer 24

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

Question 25

AA’s at physiologic pH

Answer 25

amino group is protonated
carboxylic acid group is unprotonated
due to the pKa of the side groups

Question 26

How are AA’s amphoteric molecules?

Answer 26

carboxyl groups= weakly acidic
amino groups= weakly basic
r groups= ionizable

Question 27

Zwitterion molecules

Answer 27

molecules which bear plus & minus charges simultaneously (diploar ions)

Question 28

when are AA’s Zwitterions?

Answer 28

at physiological pH

Question 29

Buffers

Answer 29

are solutions which resist a change in pH when acids or bases are added
is a mixture of either HA/A- or HB+/B

Question 30

example of how a buffer works

Answer 30

if acid is added, A- can neutralize
(->HA)
if base is added, HA can neutralize (-> A-)

Question 31

maximal buffering capacity occurs…

Answer 31

when pH=pKa (can buffer effectively within +/- 1 ph=pKa difference

Question 32

Henderson-Hasselbalch equation for Buffers

Answer 32

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)

Question 33

MOA of Pilocaprine HCl opthalamic solution

Answer 33

primary MOA: pupil constriction
secondary MOA: ciliary muscle contracts

Question 34

Pilocarpine

Answer 34

-unstable at physiologic pH
-stored at pH=4, pKa=6.6, so pH<pKa
- will exist in the protonated form (less absorption)

Question 35

Drug absorption

Answer 35

• 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)

Question 36

Renal system relationship to drug excretion

Answer 36

-weakly acidic/basic drugs are filtered at the glomeruli for excretion
-urine pH determines the amount of drug excretion/retention

Question 37

urine pH

Answer 37

alkaline urine= weakly acidic drugs excreted more rapidly
acidic urine= weakly basic drugs excreted more rapidly