Amino acid metabolism: Oxidation and Urea test 3 Flashcards
what is the process of removing ammonia from the body called?
the urea cycle
why are amino acids important?
because they are coded for the DNA and they make up proteins
what are the four fates of dietary AAs
- protein syn
- Energy production (CAC) (15-20% of total energy)
- Biosynthesis
- Urea excretion
what are the three drivers of Protein oxidation?
normal synthesis and degradation
protein rich diet
starvation or diabetes mellitus
what is the cycle that connects the urea cycle to the CAC?
Aspartate-arginino-succinate shunt of the CAC
what bonds(AAs) does pepsin target
phenylalanine
tyrosine
tryptophan
secretin does what?
stimulates release of bicarbonate from the pancreas
what does cholecystokinin do?
stimulates zymogen release from the pancreas
three fates of dietary protein enzymatically degraded to AAs?
protein synthesis
catabolized for energy within cells
transported to the liver and excreted
dietary proteins cause what to be released from the stomach?
gastrin from G cells, which causes chief cells to release pepsinogen and parietal cells to release HCl
where does most of the AA catabolism happen?
in the liver
basic strategy is to separate the amine group, and leave the carbon chain
what are the metabolically important AAs
Glutamine, Glutamate, Aspartate, Alanine
- Amine group carriers
- precursors and common metabolites
- entry and exit molecules from the CAC
How is ammonia toxic?
- it disrupts the Na/K ATPase in the CNS.
- astrocyte K uptake is disrupted
- high extracellular K prevents GABA(too much Cl in side cell)
how are amine groups stabilized?
urea or uric acid for excretion
in the transaminase rxn between alpha-ketogluterate and glutamate what enzyme does it and what stabilizes the amine group?
PLP-pyridoxal phosphate
Vitamine B6
when an AA transfers its amino group to alpha ketogluterate what is left?
alpha keto acid
what are the two major AA catabolism rxns?
transaminase and one-carbon transfers
what enzyme is responsible for glutamate becoming glutamine?
glutamine synthase
why is glutamine important?
non-toxic
most cells have glutamine synthetase
common synthetic precursor
how is intracellular ammonia buffered?
by converting glutamate to glutamine
what is the glucose-alanine cycle?
-pyruvate gets an amine group add by
alanine anminotransferase and becomes alanine.
-the amino group is coming from glutamate
-alanine then adds the amine group to alpha-ketogluterate in the liver which becomes glutamate and pyruvate is now in the liver.
why is the glucose-alanine cycle important?
allows for proteins to function as a energy source
occurs in anaerobic stress
coincides with the cori cycle
what is the purpose of the urea cycle?
to excrete liver nitrogen in the form of Urea
- requires enzymes within the mitochondria and cytoplasm
- four steps (five structural changes)
- ATP-dependent
what AA is absolutely essential for the urea cycle?
ornithine
what is the first step in the urea cycle?
Glutamine from the extrahepatic tissue
Alanine from the muscle
these the become gluatamate
once glutamate is in the mitochondrial matirx what happens?
glutamate then release ammonia to become carbamoyl phosphate
or
the amine group is added to oxaloacetate to become asparate
when ornithine adds an amine group to carbamoyl phosphate what is produced?
citrulline
**this occurs in the mitochondria
citrulline gets another amine group from aspartate and becomes what?
- arginine, **ATP dependent
- when this reacts with water urea is formed and we get ornithine once again.
- this occurs in the cytoplasm
what are the two levels of regulation for the urea cycle?
in the urea cycle itself and in the precursor step of making carbamoyl phosphate
where in the body are AAs glucogenic and ketogenic?
in the liver and only the liver
what are the six AAs degraded to pyruvate?
most energy rich
tyrptophan alanine cysteine serine glycine threonine
what are the seven AAs degraded to Acetyl-
CoA?
second most energy rich
tryptophan lysine phenylalanine tyrosine luecine isoleucine threonine
what are the five AAs degraded into alpha-ketogluterate?
3rd most energy rich
glutamate glutamine proline arginine histidine
four AAs degraded to become Succinyl-CoA?
4th most energy rich
methionine
isoleucine
valine
threonine
what AAs are degraded to become oxaloacetate?
least energy rich
Asparagine and Asparate
what are the non essential AAs?
Alanine Asparagine Aspartate Glutamate Serine
what AAs are essential (always essential) his isometeric leg lifts met failure three tries valiantly
histidine isoluecine leucine lysine methionine phenylalanine threonine tryptophan valine
which AAs are conditionally essential?
arginine cysteine glutamine glycine proline tyrosine
how is urea removed from body?
bile and urea
