Amino Acids

Lesson Learning
Outcomes
Upon completion of this lecture, students should be able to:
understand the structures and

properties of amino acids
know the groups of amino acid

What are amino acids?
Amino acids are molecules that when combined with

each other  proteins.
Amino acids contain a central tetrahedral carbon atom
(α-carbon)
amine group, carboxyl group, R-side chain
The R-side chain determines the different amino acids

There are 20 common amino acids
Amino acids can join via peptide bonds
Several amino acids occur only rarely in

proteins
Some amino acids are not found in proteins

3D structure of amino acids
Why is the 3D structure (stereochemistry) of

amino acids important?
Amino acids appear in chiral (mirror image)

except for glycine where the R = Hydrogen
Chirality of amino acids can only be seen in 3D structure The position of amino group on the left or

right side of the α-carbon determines the L or D designation.
L-amino acids are found in proteins
D-amino acids are often found in bacterial

cell walls and in some antibiotics.

There are 20 common amino acids
Amino acids can join via peptide

bonds
Several amino acids occur only rarely in proteins
Some amino acids are not found in proteins Amino Acids Can Join Via Peptide Bonds

20 Common Amino Acids
Non-polar amino acids
Polar, uncharged amino acids
Acidic amino acids
Basic amino acids

(a) nonpolar (hydrophobic)

(b) polar, neutral

c) acidic

(d) basic

Several Amino Acids Occur
Rarely in Proteins
Hydroxylysine, hydroxyproline - collagen
Carboxyglutamate - blood-clotting proteins
Pyroglutamate – in bacteriorhodopsin
Phosphorylated amino acids – a signaling device

Isoelectric point
Isoelectric point is the point along the pH

scale where the molecule (amino acid) exist in a neutral form with a zero net charge
Iso = equal

Why is it important?
So we can predict the charge of the amino acid at a certain pH
The general structure of amino acid: