Nitrogen Balance, Urea Cycle, and Amino Acid Metabolism Flashcards
Metabolic Relationships of Amino Acids
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solely ketogenic AAs
Lysine and leucine
Factors that affect Nitrogen Balance
- Positive N balance :
- Negative N balance:
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- Positive N Balance
- Intake > breakdown
- growth, pregnancy, recovery from trauma, infection or under-nutrition, insulin and androgen
- Negative N Balance
- Breakdown > intake
- inadequate protein intake, starvation, a response to trauma or infection, fever, corticosteroid hormones
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Amino groups are redistributed amoung amino acids by _________
Aminotransferases (also called transaminases).
Aminotransferases catalyze the removal of the amino group from most amino acids (therefore, FIRST step in their catabolic process)
Two amino acids that do not uses aminotransferases to catalzye the removal of its amino group
Threonine and lysine lose their amino groups via deamination.
Amine groups are transported to the liver on ________
neutral amino acids (primarily glutamine (because it is neutral, easy to pass through cell membranes into the blood stream for transport), and alanine)
These amino acids rearrange in the liver to form glutamate, aspartate, NH3 for Urea cycle
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__________ is involved in all transamination reactions
Glutamate
Transfer of an amino group from an AA to an α-ketoacid for_______, or to an α-ketoacid to form ________. The original AA then becomes an α-ketoacid, while the α-ketoacid becomes an AA.
breakdown; a nonessential AA
Aminotransferases require _________as a prosthetic group/cofactor. Reaction involves a ________intermediate
Pyridoxal Phosphate (PLP; functional form of Vit B6); Schiff’s base
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Aminotransferase Location
in most cells of the body, but predominantly in the liver and heart
Liver damage causes an increase of transaminases released into the bloodstream (diagnostic)
Common examples: SGOT/SGPT
Glutamate must be converted to ___________ to be transferred from tissues to liver
Glutamine (Glutamine Synthetase)
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Glutamine is also a precursor for __________
Asparagine (transferring the amide from glutamine to aspartate by Asparagine Synthetase)
the g-carboxyl group of aspartate must be activated by ATP before the amide group can be transferred (transamidation)
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Glutamine carries ________ from peripheral tissues to the kidneys
Hydrolytic enzymes remove the amino groups from both glutamine and asparagine
ammonia
*Liver contains both glutamine synthetase and glutaminase but the enzymes are localized in different cellular compartments.
In liver both Glutamate and Glutamine enter _______ in liver cells
mitochondria
In liver mitochondria, Glutamate Dehydrogenase releases amino group of glutamate as ammonia (oxidative deamination)
* Ammonia is toxic, this reaction occurs in mitochondria and thereby restricts amm. toxicity