Exam 2: Amino Acids #3

  1. Where do the first 2 rxns of the urea cycle occur? Where does the rest of the cycle occur?
    • 1. Mitochondria.
    • 2. Cytosol
  2. What are the three main functions of ALT and AST? Broadly. What vitamin do they require?
    • 1. Synthesis of nonessential FAs
    • 2. Production of glucose
    • 3. Loss of amino group to urea. 

    Vitamin B6
  3. What is the regulated step of the urea cycle? What is it activated by? 
    Carbamoyl phosphate synthetase I.

    N-acetylglutamate (whose syn increases with arginine, so protein rich meal) and starvation. 
  4. Is the urea cycle reversible? Which products require ATP to form and how many  ATP? How many total high energy bonds are used?
    No, the urea cycle is irreversible.

    Carbamoyl phosphate requires 2 ATP and arginosuccinate requires 1, but uses four high energy bonds. 
  5. How does a high protein meal affect carbamoyl phosphate synthetase I?
    A high protein meal is rich with arginine --> increases synthesis of N-acetylglutamate --> allosteric activator of CPS1. 
  6. How does starvation affect carbamoyl phosphate synthetase 1? 2
    Since starvation requires breakdown of body protein for energy, urea cycle will also be increased.

    Starvation upregulates autophagy and expression of urea cycle enzymes, including CPS1. 
  7. What does arginase do? Where in body is it found?
    Arginase regenerates ornithine and it is unique to the liver. 
  8. What is structure of urea? Where do its components come from? 3
    • Image Upload 1
    • C=O comes from CO2, 1 NH2 comes from free ammonia and the other comes from aspartate. 
  9. What enzyme deficiency did the little girl with hyperammonemia have? What type of gene is it?  What is the difference in activity of the enzyme for males vs females?
    She had a deficiency in oniline transcarbomylase

    It's an x-linked gene. Males can only have zero activity or 100% activity, while females can have a range of 0-100% depending on X-chromosome activity. 
  10. What compound is precursor for aspartate? How does this compound help create aspartate? With the help of what other compound? What does this other compound turn into?
    • Precursor: oxaloacetate (fumurate --> malate --> OAA)
    • By undergoing transamination, OAA --> L-aspartate with the help of glutamate which donates the a-amino group to form a-ketoglutarate. 
  11. Which compound in urea cycle is transported from mitochondria to cytosol? What enzyme does it use?
    L-citrulline. Uses ornithine transcarbmoylase
Card Set
Exam 2: Amino Acids #3
urea cycle