which of the following amino acid if added to an acidic solution will have buffer action of solution at the
physiological PH?
Answers
Answer:
An amino acid can act as a buffer because it can react with added acids and bases to keep the pH nearly constant.
The general formula of an amino acid is
H
2
NCHRCOOH
, where
R
is a side chain characteristic of each amino acid.
Because an amino acid has both an acidic group (
COOH
) and a basic group
(
NH
2
), it can act as both an acid and a base.
In very acidic media, the
NH
2
group is in the protonated form, and in very basic media, the
COOH
group is in the deprotonated form.
At an intermediate pH (the isoelectric point, pI), both ends are in their ionic form.
In glycine, the
COOH
group has
p
K
a1
=
2.34
, and the
H
3
N
+
group has
K
a2
=
9.60
.
At the isoelectric point,
p
I
=
p
K
a1
+
p
K
a2
2
=
5.97
H
3
+
N
CHRCOOH
At low pH
⇌
H
3
+
N
CHRCOO
-
At pI
⇌
H
2
NCHRCOO
-
At high pH
Amino acids have characteristic titration curves.
For example, the titration curve for glycine looks like this:
Answer:
Histidine
Explanation:
Histidine is an important amino acid, because its side chain has a pKa near the physiological pH, so it can participate as a buffer of, say, blood pH.