Acid/base properties of amino acids Flashcards
Which form is any amino acid in at pH 7?
Zwitterionic form, has both a positive and negative charge in the same molecule. The amino group is protonated and the carboxyl group is deprotonated
What are the 7 amino acids with ionizable side chains?
Arginine, tyrosine, lysine, glutamate, aspartate, histidine, cysteine
What charge does the HA and A- form of the arginine side chain have? Which form is it in at pH 7?
HA is +1
A- is 0
HA at pH 7
What charge does the HA and A- form of the tyrosine side chain have? Which form is it in at pH 7?
HA is 0
A- is -1
HA at pH 7
What charge does the HA and A- form of the lysine side chain have? Which form is it in at pH 7?
HA is +1
A- is 0
HA at pH 7
What charge does the HA and A- form of the glutamate side chain have? Which form is it in at pH 7?
HA is 0
A- is -1
A- at pH 7
What charge does the HA and A- form of the aspartate side chain have? Which form is it in at pH 7?
HA is 0
A- is -1
A- at pH 7
What charge does the HA and A- form of the cysteine side chain have? Which form is it in at pH 7?
HA is 0
A- is -1
HA at pH 7
What charge does the HA and A- form of the histidine side chain have? Which form is it in at pH 7?
HA is +1
A- is 0
Mostly A- at pH 7, about 10% is protonated
What is pI?
Isoelectric point, the pH where the net charge of the amino acid (including the side chain) is 0
How do you find the pI of a diprotic amino acid?
The average of the two pKa’s (pKa of amino and carboxyl groups)
How do you find the pI of a triprotic amino acid?
The average of the two flanking pKa’s of the form that the amino acid has a net charge of 0
How is pKa affected by the local environment?
pKa can change when there are charged and hydrophobic residues in the vicinity, which will change whether an amino acid would want to be protonated or not
