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MBC - Lecture 41
Nitrogen Incorporation, Amino Acids, and Urea (Douglas)
| Question | Answer |
|---|---|
| Lecture 41 | Nitrogen Incorporation |
| Some amino acids are ___, and are derived from ___ sources. | essential, exogenous |
| Amino acid catabolism generates ___, a nontoxic carrier of ___ atoms. | urea, nitrogen |
| Urea synthesis occurs in the ___. | liver |
| Amino acids ___ and ___ will carry amino carry amino acid nitrogen from ___ to the ___. | alanine and glutamine, peripheral tissues to the liver |
| ___ recovered from deamination of ___ in the liver provides glucose. | Pyruvate, alanine |
| Key enzymes involved in nitrogen disposal are: | transaminases, glutamate dehydrogenase, glutaminase |
| Humans make ___ non-essential amino acids de novo, and ___ essential amino acids from diet. | 11, 10 |
| Urea cycle consists of ___ steps, incorporating nitrogen from ___ and one from ___ into urea. | 4, ammonia, aspartate |
| All essential amino acids are derived from corresponding ___. | a-keto acids |
| ___ supplement is only required during growth. | Arginine |
| PVT TIM HALL | Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Arginine, Leucine, Lysine |
| Non-essential amino acids are derived by modification of metabolic intermediates from ___ and ___. | glycolysis and TCA cycle |
| Modifications involve transfer of ___ and ___. | amino groups and sulfur |
| Atmospheric nitrogen is converted to ___ and ___ by nitrogen fixing bacteria and algae. | nitrate and ammonia |
| ___ is fixed into amino acids and protein. | Ammonia |
| Nitrogen balance is the measurement of ___ minus ___. | consumption minus excretion |
| If consumption exceeds excretion, then nitrogen balance is ___. | positive (i.e. rapid growth, recovery, etc.) |
| If excretion exceeds consumption, then nitrogen balance is ___. | negative (i.e. protein malnutrition, fasting/starvation, essential amino acid deficiency) |
| ___, ___, and ___ supplements are required in premature infants and liver disease. | Cysteine, tyrosine, and arginine |
| ___ is first produced in nitrogen excretion, but is toxic. | Ammonia |
| ___ are the major sources of free ammonia. | Intestinal bacteria |
| Small amounts of ___, ___, and ___ are excreted. | uric acid, creatinine, and ammonia |
| Majority of ammonia is converted to and excreted as ___. | urea |
| BUN (___) measures ___ and ___ function. | blood urea nitrogen, metabolism and renal function |
| >___% of nitrogen excreted as ___. | >80%, urea |
| Transamination | The major process for moving nitrogen among amino acids |
| ___ is the major participant in transamination. | Glutamate |
| All amino acids except ___ and ___ undergo transamination. | lysine and threonine |
| ___ (___) is the major cofactor for transaminases. | Pyridoxyl phosphate (PLP) |
| Free ammonia in the ___ is incorporated into glutamate by ___. | liver, glutamate dehydrogenase |
| Functional form of pyridoxal phosphate, vitamin ___, is covalently linked to various aminotransferases. | vitamin B6 |
| Linkage of vitamin B6 is displaced by amino acids ___ or ___. | aspartate or glutamate |
| Drugs like ___ and ___ compete for donor amino acid binding, reducing transferase activity. | antituberculosis and isoniazid |
| High levels of ___ in blood indicates liver damage. | aminotransferases |
| AST/SGOT | Glutamate Aspartate Transferase / Serum Glutamate Oxaloacetate Transaminase |
| ALT/SGPT | Glutamate Alanine Transferase / Serum Glutamate Pyruvate Transaminase |
| ___ is released during transamination of pyridoxal phosphate. | Pyridoxamine |
| Key a-keto acid intermediates: | Pyruvate, a-Ketoglutarate, Oxaloacetate |
| Oxidative Deamination | Replace amino group with oxygen, free ammonia released |
| Dehydratase | Remove water to form an imine, then water is re-added to form keto acid and ammonia |
| Oxidative reactions release ___ and require ___ (___) as a co-factor. | free ammonia, flavin mononucleotide(FMN) |
| Dehydratase removes water and works on hydroxyamino acids ___ and ___. | serine and threonine |
| Glutamate dehydrogenase operates near ___. | equilibrium |
| ___ reducing equivalents used in amination of a-ketoglutarate. | NADPH |
| Glutamate dehydrogenase is a ___ reaction and can ___/___ ammonium to/from glutamate. | reversible, release/incorporate |
| Glutamine and asparagine amides deaminated to glutamate and aspartate by ___ and ___. | glutaminase and asparginase |
| Three enzymes that fix nitrogen into biomolecules: | Glutamine Dehydrogenase, Glutamine Synthetase, Carbamoyl Phosphate Synthetase |
| Amino group of ___ is transferred from a-ketoglutarate during metabolic interconversion to yield ___ and ___. | alanine, pyruvate and glutamate |
| Transamination of essential amino acids is ___. | unidirectional |
| All transamination reactions involve ___ and ___. | glutamate and a-ketoglutarate |
| Liver failure results in impaired ___ excretion (___ occurs). | nitrogen excretion (hyperammonemia) |
| Glucose-Alanine Cycle | Elimination of amino acids to the liver and return of carbons to peripheral tissues |
| Glutamine is synthesized by ___ to fix nitrogen in muscle for transport to the liver (some to intestine). | glutamine synthetase |
| Glutaminase and glutamate dehydrogenase release ___ to the ___ cycle. | nitrogen to the urea cycle |
| Urea synthesis occurs in the ___. | liver |
| Nitrogen in urea comes from ___ and ___. | ammonia and aspartate |
| Carbamoyl Phosphate Synthetase I (CPS I) | Catalyzes formation of carbamoyl phosphate in the mitochondria from ammonia (released from glutamine), 2 ATP, and carbon dioxide |
| Deficiency of CPS I leads to: | High blood concentrations of ammonia and related toxicity |
| CPS I requires ___ as a co-factor. | N-acetylglutamate |
| Carbamoyl Phosphate Synthetase II (CPS II) | Cytosolic form of CPS that does not require N-acetylglutamate |
| Ornithine Transcarbamoylase (OTC) | (Transferase) Catalyzes formation of citrulline in the mitochondria from ornithine and carbamoyl phosphate, releasing a Pi |
| Deficiency of ornithine transcarbamoylase leads to: | high blood concentrations of ammonia and orotic acid, as carbamoyl is shunted to pyrimidine biosynthesis |
| Argininosuccinate Synthetase | (Ligase) Catalyzes formation of argininosuccinate in the cytosol from citrulline and aspartate, requiring an ATP that is cleaved to AMP + PPi |
| Deficiency of argininosuccinate synthetase leads to: | high blood concentrations of ammonia and citrulline |
| Argininosuccinase | (Lyase) Catalyzes cleavage of argininosuccinate in the cytosol to arginine and fumarate |
| Deficiency of argininosuccinase leads to: | high blood concentrations of ammonia and citrulline |
| Arginase | (Hydrolase) Catalyzes cleavage of arginine in the cytosol to ornithine and urea |
| Deficiency of arginase leads to: | high blood concentrations of ammonia and arginine |
| If CPS I is limiting/defective, nitrogen is driven through ___ into the ___ pathway, forming orotic acid detectable in blood and urine. | CPS II into the pyrimidine pathway |
| The urea cycle is ___ in times of starvation. | up-regulated |
| CPS I is allosterically activated by ___. | N-acetylglutamate |
| ___ stimulates N-acetylglutamate synthetase. | Arginine |
| Ammonia Toxicity | Ammonia encephalopathy/cerebral edema, treat with benzoate/phenylacetate, control nitrogen intake(avoid endogenous protein breakdown), a-keto acid diet |
| CPS I/N-Acetylglutamate Deficiency | Hyperammonemia/encephalopathy/respiratory alkalosis, autosomal recessive, fatal in infants with possible delayed onset |
| OTC Deficiency | Mental Retardation/Death (NH3 accumulation), X-linked, most common urea cycle defect |
| Arginosuccinate Synthetase Deficiency | Severe hyperammonemia/increased citrulline in blood and urine, autosomal recessive, treat with low protein and arginine supplements |
| Therapy for partially defective urea cycle involves: | limit protein intake, remove excessive NH3 with compounds (benzoate and phenyl acetate) that covalently bind and are excreted, replace missing urea cycle intermediates, liver transplant |
| Majority of protein breakdown occurs in ___. | skeletal muscle |
| Urea is transported from the ___ to the ___. | liver to the kidney |
| The kidney excretes ___, ___, and ___. | ammonia, glutamate, and urea |
| Fumarate can be used in formation of ___ and __, or the reformation of ___. | ATP and glucose, aspartate |
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