Unit 4: Chapter 3 Flashcards
Amino acid structure:
alpha carbon with:
amino group (NH3+)
Carboxylic Acid (COO-)
Hydrogen atom
R group
D amino acids can occur where
nature and mostly bacterial cell walls
D Isomer of amino acids indicate
Amino Group (NH3+) is on right
D amino acids not found in
proteins
L isomer of amino acids indicate
Amino group (NH3+) is on left
At pyshiological pH 7.4, what group will be pronotated?
NH3+ or COO-
Amino group
pKa > pH
At pyshiological pH 7.4, what group will be depronotated?
NH3+ or COO-
Carboxylic group
pKa < pH
Amino acids can be sorted into four groups on basis of
general characteristics of their R groups
Nonpolar side chains of amino acids indicate:
Hydrophobic
Polar side chains of amino acids indicate:
uncharged, hydrophillic, positively charged, negatively charged
Nonpolar amino acids are typically found where in the proteins?
Interior of proteins
Polar amino acids are typically found where in the proteins?
Surface of proteins
Which side chaisnare positively charged at pH 7?
KRH
Lysine, Arginine, Histidine
What amino acid can be uncharged or positively charged at neutral pH?
Histidine
What amino acids are negatively charged at neutral pH?
D, E
glutamic acid and aspartic acid
What amino acid is least basic?
Histidine
Imidazole ring in side chain loses its proton at about pH 6 (very low)
When pKa > pH, what predominates?
weak acid predominates
H+ on, substance is protonated
When pKa < pH, what predominates?
conjugate base predominates
H+ off, substance deprotonated
Isoelectric Point (pI)
pH at which a molecule has no net charge
pI for bascic side chain
pI will be higher pH because the basic side chain introduces an “extra” positive charge
pI for acidic side chain
pI will be at a lower pH because the acidic side chain introduces an “extra” negative charge
