Nitrogen Flashcards
Nitrogen intake equal nitrogen excretion
Nitrogen Balance
Intake > ExcretionNet accumulation of proteins as in growth and pregnancy
Positive Nitrogen Balance
Intake
Negative Nitrogen Balance
Amount of protein degraded and resynthesized from amino acids
Protein Turnover
Normal Protein Turnover
300-400 g/day
Protein Degradation Mechanisms
Energy-dependent ubiquitin-proteosome mechanismNon-energy dependent degradative enzyme
Sum of all free amino acids in cells and ECF
Amino Acid Pool
3 Possible Sources of Amino Acid Pool
Degradation and turnover of body proteinDietary intakeSynthesis of nonessential amino acids
Protein digestion begins in the
Stomach
What is another substance important in vit. B12 metabolism that is also produced by parietal cells?
Intrinsic Factor
Can you name other substances absorbed by secondary active transport in the small intestines?
Glucose andGalactose
Amino Acid Metabolism: Removal of alpha-amino group (a process called deamunation) formina ammonia and a corresponding alpha-ketoacid
First Phase
What happens to ammonia?
Excreted as free ammonia in urine and stoolMajority is still converted to urea before being excreted in the urine
Major disposal form of nitrogen
Urea
Amino Acid Metabolism: Carbon skeletons of alpha-ketoacids are converted to common intermediates of energy-producing metabolic pathways
Second Phase
Seen in telostean fish, which excrete highly toxic ammonia
Ammonotelic
Seen in land animals, including humans who excrete non-toxic, water-soluble urea
Ureotelic
Seen in birds, which excrete uric acid as semisolid guano
Uricotelic
Removal of Nitrogen: First Phase
1) Transamination2) Oxidative Deamination
Occurs in all cells of body; All amino acids must transfer their amino groups to alpha-ketoglutarate to form glutamate
Transamination
Transamination: Enzymes
AminotransferasesAlanine aminotransferaseAspartate aminotransferase
Transamination: Co-enzyme
Pyridoxal phosphate (Vit. B6)
ALT is also known as
SGPT (serum glutamate: pyruvate transferase)Pyruvate and alanine interconvert with transamination
AST is also known as
SGOT (serum glutamate: OAA transferase)Aspartate and oxaloacetate interconvert with transamination
Occurs in the liver and kidney only; Only for glutamate; Glutamate is oxidized and deaminated to yield free ammonia which is used to make urea
Oxidative Deamination
Oxidative Deamination: Enzyme
Glutamate dehydrogenase
Removal of excess nitrogen from peripheral tissues: Synthesized from glutamate and ammonia; occurs in most tissues, including muscle
Through Glutamine
Removal of excess nitrogen from peripheral tissues: Excess nitrogen from the peripheral tissues can reach the liver through transamination of pyruvate to produce alanine; occurs in muscle
Through Alanine aka Glucose-Alanine Cycle
What do you call the metabolic pathway whereby lactate produced during anaerobic respiration in muscles is reconverted to glucose in the liver?
Cori Cycle
Deaminates glutamine to produce ammonium ion which is excreted from the body; Present in kidneys and small intestines
Glutaminase
Pathway for removal of Nitrogenous waste products in the body; Present only in the liver; Major disposal form of amino groups; Donors of the atoms of urea
Urea Cycle
Reactions in Urea Cycle: Step 1
Formation of Carbamoyl phosphateEnzyme: Carbamoyl phosphate synthetase I
Reactions in Urea Cycle: Step 2
Formation of CitrullineEnzyme: Ornithine transcarbamoylase
Reactions in Urea Cycle: Step 3
Synthesis of ArginosuccinateEnzyme: Argininosuccinate synthetase
Reactions in Urea Cycle: Step 4
Cleavage of Argininosuccinate to form Arginine Enzyme: Argininosuccinase
Reactions in Urea Cycle: Step 5
Arginine cleavage to yield Urea and OrnithineEnzyme: Arginase
Mnemonic: Ordinary Careless Crappers Are Also Frivolous About Urination
Ornithine + Carbamoyl Phosphate = Citrulline. + Aspartate = Argininosuccinate. = Fumarate + Arginine. = Urea + Ornithine
Rate Limiting Step of Urea Cycle
Reaction: CO2 + NH3➡️carbamoyl phosphateEnzyme: Carbamoyl phosphate synthetase I (CPS-I)Energy requirement: 4 ATPCo-factors: N-acetylglutamate, Biotin
Causes hyperammonemia, elevated blood glutamine, decreased BUN; Presents with lethargy, vomiting, hyperventilation, convulsions, cerebral edema, coma, death
Hereditary HyperammonemiaType 1: Carbamoyl phosphate synthetase I deficiencyType 2: Ornithine transcarbamoylase deficiency
Compromised liver function; Presents with tremors, slurring of speech, somnolence, vomiting, cerebral edema and blurring of vision
Acquired Hyperammonemia
Amino acid whose catabolism yields acetoacetate or acetyl-CoA or acetoacetyl-CoA
Ketogenic Amino Acid
Amino acid whose catabolism yields pyruvate or intermediates of Krebs Cycle like glucose via gluconeogenesis or glycogen in muscle or liver
Glucogenic Amino Acid
Ketogenic Amino Acid
LeucineLysine
Glucogenic and Ketogenic Amino Acid
PhenylalanineTyrosineTryptophanIsoleucine
Entry point of Amino Acids: Glutamine, Glutamate, Proline, Arginine, Histidine
Alpha-ketoglutarate
Entry point of Amino Acids: Alanine, Serine, Glycine, Cysteine, Threonine, Tryptophan
Pyruvate
Entry point of Amino Acids: Phenylalanine, Tyrosine
Fumarate
Entry point of Amino Acids: Methionine, Valine, Isoleucine, Threonine
Succinyl CoA
Entry point of Amino Acids: Aspartate, Asparagine
Oxaloacetate
Synthesis of Non-essential Amino Acid: Transamination of alpha-ketoacids
AlanineAspartateGlutamate
Synthesis of Non-essential Amino Acid: Amidation of glutamate and aspartate
GlutamineAsparagine
Synthesis of Non-essential Amino Acid: Synthesized from Glutamate
Proline
Synthesis of Non-essential Amino Acid: Made from Methionine and Serine
Cysteine
Synthesis of Non-essential Amino Acid: Made from 3-phosphoglycerate
Serine
Synthesis of Non-essential Amino Acid: Made from serine
Glycine
Synthesis of Non-essential Amino Acid: Made from phenylalanine
Tyrosine
Conversion of Amino Acid to Specialized Products: Glycine
HemePurinesCreatineAlso conjugated to bile acids
Conversion of Amino Acid to Specialized Products: Serine
Phospholipid and sphingolipidPurinesThymine
Conversion of Amino Acid to Specialized Products: Glutamate
GABA
Conversion of Amino Acid to Specialized Products: Cysteine
Thioethanolamine of CoATaurine
Conversion of Amino Acid to Specialized Products: Histidine
Histamine
Conversion of Amino Acid to Specialized Products: Arginine
CreatininePolyaminesNitric oxide
Conversion of Amino Acid to Specialized Products: Tryptophan
SerotoninNAD+NADP+MelatoninVit. B3 (Niacin)
Conversion of Amino Acid to Specialized Products: Tyrosine
CatecholaminesThyroid hormones (T3 & T4)Melanin
There is decreased phenylalanine hydroxylase or decreased tetrahydrobiopterine cofactor; Tyrosine becomes essential and phenylalanine builds up, leading to excess phenylketones in urine: phenylacetate, phenyllactate, phenylpyruvate
Phenylketonuria
Congenital deficiency of homogenistic acid oxidase in the degradative pathway of tyrosine; Resulting alkapton bodies cause urine to turn black on standing
Alkaptonuria
Congenital deficiency of either Tyrosinase or defective tyrosine transporters; Lack of melanin results in increased risk of Skin Ca; Can result from a lack of migration of neural crest cells
Albinism
All autosomal recessive; Cystathionine synthase deficiency, decreased affinity for cystathione synthase for pyridoxal phosphate, homocysteine methyltransferase deficiency
Homocystinuria
Common inherited defect of renal tubular amino acid transporter for cystine, ornithine, lysine, and arginine in the PCT o kidneys
Cystinuria
Blocked degradation of branched amino acids due to a deficiency in alpha-ketoacid dehydrogenase; Causes an increased alpha-ketoacid in the blood, especially leucine
Maple Syrup Urine Disease
Cyclic compounds formed by the linkage of four pyrrole rings through methyne bridges; Form complexes with metal ions bound to nitrogen atom of the pyrrole rings
Porphyrins
Heme Synthesis: Step 1
Formation of δ-Aminolevulinic AcidRate limiting stepReaction: Glycine + Succinyl CoA➡️δ-Aminolevulinic AcidEnzyme: ALA synthaseCo-factor: Pyridoxine
Heme Synthesis: Step 2
Formation of PorphobilinogenCondensation of two molecules of ALA by zinc-containing ALA dehydratase
Heme Synthesis: Step 3
Formation of Uroporphyrinogen
Heme Synthesis: Step 4
Formation of hemeIntroduction of iron into protoporphyrin IX occurs spontaneously but the rate is enhanced by ferrochelatase
In which of the following reactions or pathways is vitamin B6 (pyridoxine) not a co-factor?
Oxidation of pyruvate to acetyl CoA
Genetic or acquired disorders due to abnormalities in the pathway of biosynthesis of heme; Most common: Porphyria Cutanea Tarda
Porphyrias
Pyridoxine deficiency associated with Isoniazid therapy
Sideroblastic Anemia with Ringed Sideroblasts
Heme synthase introduces the Fe2+ into protoporphyrin IX to make the heme ring
Iron Deficiency
Inactivates many enzymes in heme synthesis: ALA dehydratase or Ferrochelatase
Lead Poisoning
Common Patterns of Anemia: Microcytic, Hypochromic
Iron deficiency anemiaThalassemiasLead poisoning
Common Patterns of Anemia: Megaloblastic
Folate or vitamin B12 deficiencyPernicious anemia
Common Patterns of Anemia: Normocytic, Normochromic
Anemia of Chronic IllnessChronic Kidney Disease
Common Patterns of Anemia: Increased MCHC
Spherocytosis
After 120 days, RBCs are taken up and degraded by the reticuloendothelial system, particularly in the liver and spleen
Degradation of Heme