Acid Base properties of the amino acids Flashcards
1
Q
pKa definition
A
The pH at which a weakly acidic group is 50% dissociated
2
Q
pKa of amino acids
A
Every AA has 2 weakly ionising groups (Alpha - COOH and alpha Nh3+) therefore has 2 pKa values
3
Q
Typical pKa values of COOH and NH3+
A
COOH - 2.3
NH3+ - 9.7
4
Q
Acid base nature RULE
A
At a pH below the pKa value the protonated dominates(eg.COOH) dominates and above the pKa value the deprotonated form dominates(Eg. COO-)
5
Q
Ionising groups dissociate in order of increasing pKa
A
The group with lowest pKa is the most strongly ionising one and will dissociate first. For all amino acids this will be the alpha COOH as it has the lowest pKa value
6
Q
How to caclulate the net charge of an AA
A
- Decide which form is present for each group
- Using the charge on each group add them together to find the net charge
7
Q
A
8
Q
A
9
Q
A
10
Q
A
11
Q
A
