Amino Acids

Chapter 4 . Amino Acids
+H 3N
H
COO-
C
C
H
CH 3
OH
H
HO
COO-
C
C
CH 3
NH 3+
H
58
+H 3N
COO-
C
C
CH 3
H
H
H
COO-
C
C
CH 3
NH 3+
L-Threonine D-Threonine L-Allothreonine D-Allothreonine
By inspection we see that
L-threonine is (2S, 3R) threonine
D-threonine is (2R,3S) threonine
L-allothreonine is (2S,3S) threonine
D-allothreonine is (2R,3R) threonine
Questions for Self Study
1. Fill in the blanks: A bond is an amide bond between two . The bond is formed by a
reaction between the of one amino acid and the of a second amino acid with the
elimination of the elements of . The result is a linear chain with an end and a end.
The chain can be extended into a polymer with additional amino acids. The polymer formed is
called either a or a depending on the number of amino acids joined. The amide bond
can be broken by the addition of the elements of water across it in a reaction.
2. List the four classes of amino acids.
3. Indicate which class of amino acids best represents the statements presented below:
a. Their side chain may contain a hydroxyl group. .
b. Negatively charged at basic pH. .
c. Relatively poorly soluble in aqueous solution. .
d. Relatively soluble in aqueous solution. .
e. Positively charged at acidic pH. .
f. Side chains are capable of hydrogen bonding. .
g. Includes the amino acids arginine, histidine and lysine. .
h. Side chains contain predominantly hydrocarbons._____
i. Side chains are responsible for the hydrophobic cores of globular proteins. .
j. The amides of glutamic and aspartic acid belong to this group. .
4. From the list of amino acids presented indicate which one best fits the description:
a. The smallest amino acid (It also lacks a stereoisomer).
alanine, glycine, phenylalanine, glutamine
b. An aromatic amino acid.
glutamic acid, tyrosine, isoleucine, proline
c. A sulfur-containing amino acid.
methionine, aspartic acid, arginine, leucine
d. An amino acid capable of forming sulfur-sulfur bonds.
methionine, proline, cysteine, tryptophan
e. A branched chain amino acid.
methionine, leucine, aspartic acid, asparagine
5. Fill in the blanks. Most of the amino acids are chiral compounds because they have at least
one carbon atom with different groups attached. Thus, there are ways of arranging the
four groups about the carbon atom. For the case of an amino acid with a single asymmetric
carbon, the isomers pairs that can be formed are called ; they are nonsuperimposable, .
images of each other. Using the D,L system of nomenclature, the commonly occurring amino
acids are all amino acids.
6. Which three amino acids absorb light in the ultraviolet region of the spectrum above 250
nm?
HO
H
OH