Amino acid charge, pH and Structure Flashcards
what is a zwitterion?
A neutral ion with (-) and (+) charges- overall neutral charge
what is the charge of the amino and carboxyl group of an amino acid at pH 7?
amino-NH3+
carboxyl- COO-
what is the charge of the carboxyl group of an amino acid when pKa is < 7 but >1?
COO-
pka ~2
-deprotonation of the carboxyl
what is the charge of the carboxyl group of an amino acid when pH is >7 but < 14?
COO-
pka ~2
-deprotonation of the carboxyl
what is the charge of the amino group of an amino acid when pH is 14 ?
NH2
pka ~9.5
what is the charge of the amino group of an amino acid when pH is equal or less than 7?
NH3+
pka~9.5
In a low pH solution will the ionizable groups be protonated or deprotonated?
protonated
In a high pH solution will the ionizable groups be protonated or deprotonated?
deprotonated
what is pKa? what does it tell us?
-a measure of protonation or deprotonation relative to pH
- tells us the strength of a weak acid; it’s tendency to ionize
low pKa = more dissociation
lower pKa = stronger acid
what does it mean if pKa > pH?
the protonated fraction is greater than the deprotonated fraction
[HA] > [A-]
what does it mean if pKa < pH?
the protonated fraction is less than the deprotonated fraction
[A-] > [HA]
what amino acids are non-polar at pH 7?
alanine, valine, phenylalanine, tryptophan, leucine, isoleucine, methionine, proline
what amino acids are polar uncharged at pH 7?
serine, threonine, tyrosine, cysteine, asparagine, glutamine, histidine, glycine*weakly polar
what is the pKa of tyrosine ?
> 7
10.5
what R groups have ionizable functional groups?
Neutral polar- tyrosine, cysteine and histidine
charged polar- asparagine, glutamine , lysine, and arginine
what polar charged R groups are neutral at high pH?
Lysine and arginine
what polar charged groups are neutral at low pH?
Asparagine and glutamine
what neutral polar R group is (+) at low pH?
histidine
pka ~6.0
what neutral polar R groups are (-) at high pH?
tyrosine and cysteine
pka~10.5 and 8.5 respectively
what is the pKa of cysteine
> 7
8.5
what is the pKa of Histidine?
<7
6.0
-acts as a donor and a base
what are the polar charged amino acids at pH 7?
aspartate, glutamate, lysine, arginine
pka ~4.0, 4.0, 10.0 and 12.5 respectively
what is the charge of aspartate at pH 7? what’s it’s pKa?
(-) at pH 7
pKa = 4.0
what is the charge of glutamate at pH 7? what’s it’s pKa?
(-) at pH 7
pKa = 4.0
what is the charge of lysine at pH 7? what’s it’s pKa?
(+) at pH 7
pKa = 10.0
what is the charge of arginine at pH 7? what is its pKa?
(+) at pH 7
pKa = 12.5
