Amino Acid Degradation and the Urea Cycle Flashcards
how are amino acids metabolized?
You can get rid of the amino group from amino acids and the remaining carbon skeleton can be fed into either glycolysis or the TCA cycle. The amino group is removed via a transamination reaction.
What happens to amino groups?
They are funneled onto alpha-ketoglutarate to form glutamate. Glutamate goes to the liver, which is where the Urea cycle happens.
alanine
can transfer its amino group onto alpha-ketoglutarate to form pyruvate and glutamate. glutamate goes to the liver to get rid of amino group. Pyruvate can feed into oxidation of pyruvate or used in gluconeogenesis.
Aspartate
can transfer its amino group to alpha-ketoglutarate to form oxaloacetate and glutamate. Glutamate goes to the liver to get rid of amino group, and oxaloacetate feeds into TCA cycle or can be used for gluconeogenesis.
Glutamate dehydrogenase
The enzyme in the mitochondria that releases NH4+ in the oxidative deamination of glutamate
alpha-amino acid + NAD+ + H20 –>
the coupled reactions of aminotransferases and glutamate dehydrogenase
Amino acids that can be directly deaminated
serine –> pyruvate + NH4+
Threonine –> alpha-ketobutyrate + NH4+
glutamate –> alpha-ketoglutarate + NH4+
How does NH4+ get out of the body?
It is carried on glutamate or glutamine to the liver, where it can enter the urea cycle and be excreted in urine.
Glutamine synthetase
Transfers amino group from glutamate to glutamine. Glutamine can be transported in the blood to the liver, which can remove both amino groups from glutamine.
ketogenic amino acids
amino acids metabolized to acetyl CoA or acetoacetyl CoA - they can form fats but not glucose
gluconeogenic amino acids
amino acids that can be used to synthesize glucose
Leucine and Lysine
the two amino acids that are solely ketogenic
Urea cycle location
liver
Urea cycle
Ammonia is carried by glutamate or glutamine to the liver. In the mitochondria of the liver cell, the following reaction occurs:
CO2 + NH4+ –> carbamoyl phosphate (requires 2 ATP)
Carbamoyl phosphate enters the urea cycle. In the mitochondrial matrix, carbamoyl phosphate fuses with ornithine to form citrulline. Citrulline moves out to the cytoplasm, where it fuses with aspartate to form argininosuccinate and eventually fumarate.
carbamoyl phosphate
Formed by carbon dioxide and ammonium fusing, catalyzed by carbamoyl phosphate synthetase 1. The phosphate group comes from ATP, which is used as energy for the reaction.
