Chapter 17 Amino acid metabolism

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• Chapter 17 Amino acid metabolism
• Nitrogen and the biosphere
• Nitrogen fixation
• Amino acid biosynthesis
• Amino acid degradation including
• the urea cycle

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1. Nitrogen and the biosphere.
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• Nitrogen fixation
• is carried out by symbiotic bacteria that
• grow in root nodules of plants (legumes).

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Nitrogenase N2 8 H 16 ATP ? 2 NH3 H2
16 ADP 16 P
anaerobic
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• Amino acid biosynthesis
• A. Essential amino acids
• B. Incorporation of the amino
• group.
• C. Synthesis of carbon skeletons

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• Essential amino acids

Do not Memorize.
C F
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B. Incorporation of the amino group.

• Reductive amination
• Amidation

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1) Reductive amination
Glutamate dehydrogenase
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2) Amidation
Glutamine synthetase
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How is the amino group transferred to
other amino acids. Tranamination. Pyridoxal
phosphate
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• Amino acid carbon skeletons
• can be made from
• 1. Citric acid cycle
• Alpha-ketoglutarate
• Oxaloacetate
• Glycolysis
• 3-phosphoglycerate
• Pyruvate
• Phosphoenolpyruvate
• 3. Pentose phosphate pathway
• Ribose-5-phosphate

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Amino acids can be divided into families. For
example, serine, cysteine and glycine are
derived from 3-phosphoglycerate. See (but dont
memorize) Fig. 17.9 on p. 526
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Also need 1 C units. Transferring 1C units
carried by Biotin Folic acid S-adenoxyl
methionine
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• Amino acid catabolism
• A. Remove the amino group
• B. Process the carbon skeleton
• C. What happens to the amino
• group after it is removed?

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A. Removal of the amino group.

• First step is removal of the ?-amino group by
  transamination
• it is transferred to ?-ketoglutarate to give
  glutamate and an ?-ketoacid

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• What happens to the carbon skeletons?

• Two pathways
• Into glycolysis (pyruvate)
• or the citric acid cycle
• alpha-ketogluarate
• succinyl CoA\\
• fumerate
• 2 ) acetyl CoA
• to citric acid cycle
• ketone bodies.

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• Getting rid of excess nitrogen
• The urea cycle.

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• The ?-amino group which has been transferred to
  ?-ketoglutarate may
• be used for biosynthesis
• excreted as one of the following

Fish Mammals
Birds
Kangaroo
Rat
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Removal of the ammonia. urea cycle 1. Removal
of the ammonia. 2. Formation of carbamoyl
phosphate 3. The urea cycle proper.
1.
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• Removal of the ammonia
• glutamate dehydrogenase
• working backwards.

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2. Formation of carbamoyl phosphate
Mitochondria
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3. The urea cycle.- Step 1
Mitochondria
p552
citrulline
ornithine
Cytoplasm
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Ornithine citrulline
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citrulline
2nd NH2
ornithine
Argino- succinate
ATP required