Chapter 3: Amino Acids Flashcards
Amino acids (a.a.) bond to a alpha-carbon and are C–…..
Chiral (exist as two mirror images)
Which a.a. isomer is preferred? L or D?
L-isomer (slightly more soluble)
What is the charge of the functional groups when pH is 0~2?
NH3+ and COOH (both are protonated)
What is the charges of functional groups when pH is 2-9
NH3+ and COO- (Zwitterion)
What is the charges of functional groups when pH is 9-14
NH2- and COO- (both are deprotonated)
Simple Hydrophobic a.a.
R-groups –> simple saturated hydrocarbons
- Alanine (Ala)
-Valine (Val)
- Leucine (Leu)
- Isoleucine (Ile)
+ Glycine (Gly) - no hydrocarbons - only exception
Complex Hydrophobic a.a
R-groups: Complex structures including 2 with aromatic rings
- Methionine (Met) - has a Methyl thioether (S—CH3)
-Proline (Pro) - side chain is linked to amine
-Phenylalanine (Phe) - aromatic ring
-Tryptophan (Trp) - aromatic ring
Neutral Polar a.a.
R-groups: Polar (hydrophilic)
-neutral + electronegative dipoles
- Serine (Ser)
- Threonine (Thr)
- Tyrosine (Tyr)
- Cysteine (Cyr) contains sulfhydryl (-SH)
- Asparagine (Asn) contains terminal carboxamide
- Glutamine (Gln) contain terminal carboxamide
Positively charged polar a.a.
R-groups: Polar (hydrophilic) with positive charge
- Lysine (Lys)
- Arginine (Arg) contains a guanidinium group
- Histidine (His) - contains an imidazole group (aromatic ring)
Negatively Charged (acidic) a.a.
R-groups: Polar (hydrophilic) Carboxy R groups
- Aspartate
-Glutamate
+can add amine groups to hydroxy position of carboxy R group to make neutral polar Asp and Glu
Which 7 a.a. can be protonated?
- Cysteine (pKa 8.3)
- Tyrosine (pKa 10.9)
- Histidine (pKa 6.0)
- Lysine (pKa 10.8)
- Arginine (pKa 12.5)
- Glutamic acid (pKa 4.1)
- Aspartic acid (pKa 4.1)
Why are some a.a. considered nonessential?
a.a that the human body can make naturally.
