Download 24.9 Synthesis of Amino Acids

24.9 Synthesis of Amino Acids
Plants and bacteria produce all of their
amino acids using NH4+ and NO3–.
• Humans can synthesize 9 of the 20
amino acids found in their proteins.
• Nonessential amino acids are
synthesized in the body, while
essential amino acids must be
obtained from diet.
Learning Goal Illustrate how some
nonessential amino acids are
synthesized from intermediates in
the citric acid cycle and other
metabolic pathways.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Pathways for Amino Acid Synthesis
A variety of pathways are involved in the synthesis
of nonessential amino acids.
• The body synthesizes nonessential amino acids.
• The α-keto acid carbon skeletons are obtained
from the citric acid cycle or glycolysis and
converted to amino acids by transamination.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Synthesis of Amino Acids
Nonessential amino acids are synthesized from
intermediates of glycolysis and the citric acid cycle.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Synthesis of Alanine, Aspartate
Nonessential amino acids such as alanine and
aspartate are produced by transamination.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Synthesis of Glutamine
The synthesis of the other nonessential amino acids
may require several reactions in addition to
transamination.
Glutamine is synthesized when a second amino group
is added to glutamate using the energy from the
hydrolysis of ATP
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Synthesis of Tyrosine
Tyrosine, an aromatic amino acid with a hydroxyl
group, is formed from phenylalanine, an essential
amino acid, and oxygen.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Overview, Metabolism
Catabolic pathways
• degrade large molecules.
• form small molecules that enter the citric acid cycle and
electron transport to produce energy.
Anabolic pathways
• use small molecules and energy.
• synthesize larger molecules in the cell.
In the overall view of metabolism, there are several branch
points from which compounds may be degraded for
energy or used to synthesize larger molecules.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Overview, Metabolism
Core Chemistry Skill
Distinguishing Anabolic
and Catabolic Pathways
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Match each of the following amino acids with the
intermediate needed for its synthesis:
1) alanine 2) glutamate 3) aspartate
A. pyruvate
B. oxaloacetate
C. α-ketoglutarate
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Match each of the following amino acids with the
intermediate needed for its synthesis:
1) alanine 2) glutamate 3) aspartate
A. pyruvate
1) alanine
B. oxaloacetate
3) aspartate
C. α-ketoglutarate
2) glutamate
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Chemistry Link to Health:
Phenylketonuria (PKU)
In phenylketonuria (PKU),
• the gene that converts phenylalanine to tyrosine is defective.
• phenylalanine forms phenylpyruvate (transamination), which
goes to phenylacetate (decarboxylation).
• high levels of phenylacetate cause severe mental
retardation.
• a diet low in phenylalanine and high in tyrosine is
recommended.
• sweeteners and soft drinks containing aspartame, which
contains phenylalanine as one of the two amino acids in its
structure, should be avoided.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Chemistry Link to Health:
Phenylketonuria (PKU)
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Concept Map
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.