OpenStax Organic Chemistry: A Tenth Edition Student Solutions Manual
Chapter 26 – Biomolecules: Amino Acids, Peptides and Proteins
Solutions to Problems
26.1 Amino Acids with aromatic rings: Phe, Tyr, Trp, His.
Amino acids containing sulfur: Cys, Met.
Amino acids that are alcohols: Ser, Thr (Tyr is a phenol.)
Amino acids having hydrocarbon side chains: Ala, Ile, Leu, Val, Phe.
26.2
A Fischer projection of the α-carbon of an L-amino acid is pictured above.
26.3
26.4 On the low pH (acidic) side of pI, a protein has a net positive charge, and on the high pH
(basic) side of pI, a protein has a net negative charge. Thus, hemoglobin (pI = 6.8) has a
net positive charge at pH =5.3 and a net negative charge at pH = 7.3.
26.5 This method of amino acid synthesis is simple and uses methods we have already studied.
The phthalimide synthesis can also be used to introduce the amino group. Remember that
only racemic amino acids are produced by this method.
1 11/6/2023
, OpenStax Organic Chemistry: A Tenth Edition Student Solutions Manual
(a)
(b)
26.6
In the amidomalonate synthesis, shown above, an alkyl halide RX is converted to
RCH(NH3+)CO2H. Choose an alkyl halide that completes the structure of the target
amino acid.
Amino Acid Halide
(a)
(b)
(c)
11/2/2023 2
, OpenStax Organic Chemistry: A Tenth Edition Student Solutions Manual
(d)
26.7 The precursor to an amino acid prepared by enantioselective hydrogenation has a Z
double bond conjugated with a carboxylic acid carbonyl group.
26.8 Val–Tyr–Gly (VYG) Tyr–Gly–Val (YGV) Gly–Val–Tyr (GVY)
Val–Gly–Tyr (VGY) Tyr–Val–Gly (YVG) Gly–Tyr–Val (GYV)
26.9
26.10
The cysteine sulfur is a good nucleophile, and iodide is a good leaving group.
26.11 One product of the reaction of an amino acid with ninhydrin is the extensively conjugated
purple ninhydrin product. The other major product is the aldehyde derived from the side
chain of the amino acid. When valine reacts, the resulting aldehyde is 2-methylpropanal.
The other products are carbon dioxide and water. The identity of the aldehyde is
determined by the amino acid side chain.
3 10/26/2023
Chapter 26 – Biomolecules: Amino Acids, Peptides and Proteins
Solutions to Problems
26.1 Amino Acids with aromatic rings: Phe, Tyr, Trp, His.
Amino acids containing sulfur: Cys, Met.
Amino acids that are alcohols: Ser, Thr (Tyr is a phenol.)
Amino acids having hydrocarbon side chains: Ala, Ile, Leu, Val, Phe.
26.2
A Fischer projection of the α-carbon of an L-amino acid is pictured above.
26.3
26.4 On the low pH (acidic) side of pI, a protein has a net positive charge, and on the high pH
(basic) side of pI, a protein has a net negative charge. Thus, hemoglobin (pI = 6.8) has a
net positive charge at pH =5.3 and a net negative charge at pH = 7.3.
26.5 This method of amino acid synthesis is simple and uses methods we have already studied.
The phthalimide synthesis can also be used to introduce the amino group. Remember that
only racemic amino acids are produced by this method.
1 11/6/2023
, OpenStax Organic Chemistry: A Tenth Edition Student Solutions Manual
(a)
(b)
26.6
In the amidomalonate synthesis, shown above, an alkyl halide RX is converted to
RCH(NH3+)CO2H. Choose an alkyl halide that completes the structure of the target
amino acid.
Amino Acid Halide
(a)
(b)
(c)
11/2/2023 2
, OpenStax Organic Chemistry: A Tenth Edition Student Solutions Manual
(d)
26.7 The precursor to an amino acid prepared by enantioselective hydrogenation has a Z
double bond conjugated with a carboxylic acid carbonyl group.
26.8 Val–Tyr–Gly (VYG) Tyr–Gly–Val (YGV) Gly–Val–Tyr (GVY)
Val–Gly–Tyr (VGY) Tyr–Val–Gly (YVG) Gly–Tyr–Val (GYV)
26.9
26.10
The cysteine sulfur is a good nucleophile, and iodide is a good leaving group.
26.11 One product of the reaction of an amino acid with ninhydrin is the extensively conjugated
purple ninhydrin product. The other major product is the aldehyde derived from the side
chain of the amino acid. When valine reacts, the resulting aldehyde is 2-methylpropanal.
The other products are carbon dioxide and water. The identity of the aldehyde is
determined by the amino acid side chain.
3 10/26/2023
