Basics
DOUBLE JEOPARDY!
How are amino acids obtained?
What happens to excess amino acids?
Through diet.
Since amino aids cannot be stored, excess amino acids are degraded.
What are organisms that excrete excess NH4+ as urea called?
Ureotelic organisms.
What are aminotransferases (transaminases)?
Enzymes that transfer amino groups from an amino acid to alpha-ketoglutarate to generate glutamate.
DOUBLE JEOPARDY!
Where do the beginning steps of the urea cycle occur?
Where do the last steps of the urea cycle occur?
Mitochondria.
Cytoplasm.
What is the first step of amino acid degradation?
Nitrogen removal.
What is the difference between monooxygenases and dioxygenases?
Monooxygenases incorporate one atom of O2 into the product and the other into water.
Dioxygenases incorporate both atoms of O2 into the product.
What kind of enzymes are required for the degradation of aromatic amino acids?
Oxygenases.
How are alpha amino groups converted into ammonium ions?
aplha-amino group is transferred to aplha-ketoglutarate → funneled to glutamate → deaminated into NH4+ (ammonium ion)
In terrestrial vertebrates, what is the ultimate fate of NH4+?
Formation of urea.
What amino acids can be directly deaminated?
Serine and Threonine.
What is the key regulatory enzyme for urea synthesis?
Carbamoyl phosphate synthetase.
How is carbamoyl phosphate formed?
Coupling of ammonium with bicarbonate, catalyzed by carbamoyl phosphate synthetase (CPS 1).
What is the first priority use of amino acids?
Building blocks/Precursors for proteins or other biomolecules.
How is the urea cycle linked to gluconeogenesis?
Fumarate can be converted into oxaloacetate by the citric acid cycle and then into glucose by the gluconeogenic pathway.
What enzyme, found in the mitochondria, releases NH4+ in the oxidative deamination of glutamate?
Glutamate dehydrogenase.
What are the steps of the glucose-alanine cycle?
Muscles use amino acids for fuel. The removed nitrogen is transferred through glutamate to alanine. Alanine is picked up by the liver to form pyruvate, to then form glucose.
Why would cellular proteins be degraded into amino acids?
Because of damage or for regulatory purposes.
DOUBLE JEOPARDY!
How many metabolic intermediates can be made from the carbon skeletons of amino acids?
Can you name three?
Seven.
1. pyruvate 2. acetyl CoA 3. acetoacetyl CoA 4. alpha-ketoglutarate 5. succinyl CoA 6. fumarate 7. oxaloacetate
DOUBLE JEOPARDY!
What is an abortive complex?
Where is this seen in the degradation of amino acids? (What enzyme is it formed on?)
An abortive complex is formed on an enzyme when a product is replaced by substrate before the reaction is complete.
This is seen on the glutamate dehydrogenase.
Carbamoyl phosphate reacts with ornithine to begin the urea cycle. Explain how through this cycle, the cycle is prepped to run again.
The carbamoyl group is transferred to ornithine to form citrulline which is transported out of the mitochondria to the cytoplasm in exchange for ornithine. This ornithine that is exchanged is a product of the end step (Arginine being cleaved into urea and ornithine - which is then transported into the mitochondria to begin another cycle).