Download 24.8 Fates of the Carbon Atoms from Amino Acids

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Transcript
24.8 Fates of the Carbon Atoms from
Amino Acids
Carbon atoms from
degraded amino acids
are converted to the
intermediates of the
citric acid cycle or
other pathways.
Learning Goal
Describe where
carbon atoms from
amino acids enter
the citric acid cycle
or other pathways.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Carbon Atoms from Amino Acids
We can classify the amino acids according to the number
of carbon atoms.
• Amino acids that provide three-carbon compounds are
converted to pyruvate.
• Amino acids with four carbon atoms are converted to
oxaloacetate.
• Five-carbon amino acids provide α-ketoglutarate.
Some amino acids are listed twice because they can
enter different pathways to form citric acid cycle
intermediates.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Amino Acid Pathways to Citric Acid
Intermediates
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Glucogenic and Ketogenic Amino Acids
Amino acids are classified as
• glucogenic if they generate pyruvate,
α-ketoglutarate, succinyl-CoA, fumarate, or
oxaloacete, which can be used to synthesize
glucose.
• ketogenic if they generate acetoacetyl-CoA or
acetyl-CoA, which can form ketone bodies or
fatty acids.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Match each of the following citric acid intermediates
with the amino acid that provides its carbon skeleton:
1) pyruvate 2) fumarate 3) α-ketoglutarate
A. cysteine
B. glutamine
C. aspartate
D. serine
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Match each of the following citric acid intermediates
with the amino acid that provides its carbon skeleton:
1) pyruvate 2) fumarate 3) α-ketoglutarate
A. cysteine
1) Pyruvate
B. glutamine
3) α-ketoglutarate
C. aspartate
2) Fumarate
D. serine
1) pyruvate
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.