Urea Cycle - Study Guide Flashcards
what is nitrogen balance?
The healthy human adult is in nitrogen balance which means the amount of nitrogen excreted (mainly through urine) equals the amount consumed (dietary protein).
what is negative nitrogen balance?
– The amount of nitrogen excreted is greater than the amount consumed.
– Associated with burns, tissue injury, wasting diseases, fevers, periods of fasting. Can be used as part of a clinical evaluation of malnutrition.
what is positive nitrogen balance?
– The amount of nitrogen excreted is less than the amount consumed.
– Associated with periods of growth, hypothyroidism, tissue repair, and pregnancy.
• Typical of growing children: lots of amino acid and protein synthesis.
what supplies the amino acid pool?
degradation of endogenous body proteins
exogenous dietary protein
Nonessential amino acids synthesized from simple intermediates of metabolism
how is the amino acid pool depleted?
Synthesis of body protein (translation)
Consumption of amino acids as precursors of essential nitrogen-containing small molecules (e.g. hormones, heme, neurotransmitters)
Conversion of amino acids to glucose, glycogen, fatty acids, and ketone bodies, or oxidation to CO2 + H2O
what is protein turnover?
The simultaneous synthesis and degradation of protein molecules
In healthy well-fed individuals, the input into the amino acid pool is balanced by the output
Therefore, the amount in the amino acid pool is constant (steady state) and the individual is in nitrogen balance
what is the function of ALT?
ALT used for gluconeogenesis
what is the function of AST?
AST used for the first bypass in the liver and these enzymes are found in the liver.
what is the effect if we see elevated AST or ALT levels?
People with liver disease will have elevated levels of these enzymes in the blood.
when would see that AST/ALT levels be elevated?
Particularly high in conditions that cause cell necrosis, such as severe viral hepatitis, chronic alcoholic cirrhosis, and prolonged circulatory collapse
what enzymes are measured and are useful in determining the course of liver damage?
AST and ALT, used for liver function tests
what reaction is NAD+ primarily used in? is this catabolic or anabolic?
oxidative deamination (loss of ammonia coupled with the oxidation of the carbon skeleton)
catabolic
what is NADPH primarily used in? is this catabolic or anabolic?
reductive amination (gain of ammonia coupled with the reduction of the carbon skeleton)
anabolic
how is the direction of the reaction determined based on NAD+ or NADPH?
Direction of reaction depends on the relative concentrations of glutamate, α-ketoglutarate, ammonia, and the ratio of oxidized to reduced coenzymes
- Ingestion of high protein meal ↑glutamate levels.. Reaction proceeds in direction of amino acid degradation
- ↑ammonia levels…. Reaction proceeds in direction to glutamate synthesis
