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Jaspie - Biochemistry II > Nitrogen metabolism > Flashcards

Nitrogen metabolism Flashcards

1
Q

Net accumulation of proteins as in growth & pregnancy

A

Positive Nitrogen Balance

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2
Q

Net breakdown of protein as in surgery, advanced cancer, kwashiorkor or marasmus, starvation

A

Negative Nitrogen Balance

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3
Q

Protein Turnover per day

A

300-400g/day

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4
Q

Energy-dependent protein degradation mechanism

A

Ubiquitin-Proteasome Mechanism

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5
Q

Protein Degradation: Endogenous

A

Proteasome

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6
Q

Protein Degradation: Exogenous

A

Lysosome

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7
Q

Sum of all free AAs in cells and ECF, degradation and turnover of body protein, dietary intake, synthesis of non-essential AAs

A

Amino Acid Pool

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8
Q

Resorption of Proteins per day

A

150g/day

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9
Q

Degradation of Proteins per day

A

50-100g/day

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10
Q

Protein Digestion: Stomach

A

HCl, Pepsin

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11
Q

Protein Digestion: Pancreatic Enzymes

A

Zymogens activated by Trypsin

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12
Q

Protein Digestion: liberate AAs and dipeptides

A

Aminopeptidases

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13
Q

Protein Digestion: absorbed by secondary active transport

A

Free AAs

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14
Q

Protein Digestion: Endopeptidases

A

Trypsin, Chymotrypsin, Elastase

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15
Q

Protein Digestion: Exopeptidases

A

Carboxypeptidase, Aminopeptidase

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16
Q

HCl is produced by

A

parietal cells

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17
Q

Pepsinogen is produced by

A

chief cells

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18
Q

AA Catabolism: removal of the α-amino group (deamination) forming ammonia and a corresponding α-ketoacid

A

First Phase

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19
Q

AA Catabolism: carbon skeletons of α-ketoacids are converted to common intermediates of energy-producing metabolic pathways (Glycolysis, Krebs Cycle)

A

Second Phase

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20
Q

Major disposal form of nitrogen

A

Urea

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21
Q

Nitrogen Excretion: seen in telostean fish, excrete highly toxic ammonia

A

Ammonotelic

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22
Q

Nitrogen Excretion: land animals, humans, non-toxic water-soluble urea

A

Ureotelic

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23
Q

Nitrogen Excretion: birds, secrete uric acid as semisolid guano

A

Uricotelic

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24
Q

Main steps in removing nitrogen from AA

A

transamination, oxidative deamination

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25
Q

AA Nitrogen Removal: occurs in all cells of the body, all AAs must transfer their amino groups to α-ketoglutarate to form glutamate (except lysine & threonine)

A

Transamination

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26
Q

Aminotransferases

A

Alanine Aminotransferase (ALT), Aspartate Aminotransferas (AST)

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27
Q

Aminotransferases: Co-Enzyme

A

Pyridoxal Phosphate (B6)

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28
Q

ALT is also known as

A

SGPT (serum glutamate:pyruvate transferase)

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29
Q

ALT/SGPT transaminates

A

pyruvate, alanine

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30
Q

AST is also known as

A

SGOT (serum glutamate:OAA transferase)

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31
Q

AST/SGOT transaminates

A

aspartate, OAA

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32
Q

AA Nitrogen Removal: occurs in the liver and kidney, only for glutamate, glutamate is oxidized and deaminated to yield free ammonia (NH3) which is used to make urea

A

Oxidative Deamination

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33
Q

Oxidative Deamination: Enzyme

A

Glutamate Dehydrogenase

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34
Q

Peripheral Nitrogen Removal: synthesized from glutamate and ammonia, occurs in most tissues, including muscle

A

Glutamine

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35
Q

Peripheral Nitrogen Removal: excess nitrogen from the peripheral tissues can reach the liver through transamination of pyruvate, occurs in muscle

A

Alanina

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36
Q

In the liver, alanine is converted back to pyruvate which may undergo gluconeogenesis which can be transported back to the muscles

A

Glucose, Alanine Cycle

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37
Q

Deaminates glutamine to produce ammonium ion (NH$+) which is excreted from the body, eliminates ammonium ion in the urine (kidneys), ammonium ion sent to the liver via the portal circulation for the urea cycle (SI)

A

Glutaminase

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38
Q

Krebs-Henseleit Cycle/Ornithine Cycle

A

Urea Cycle

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39
Q

Pathway for removal of nitrogenous waste products in the body, present only in the liver, major disposal of amino groups

A

Urea Cycle

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40
Q

Donors of the atoms of urea

A

NH3 from free ammonia and aspartate, C from CO2

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41
Q

Urea Cycle: only _____ can penetrate the mitochondrial membrane

A

Citrulline

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42
Q

Urea Cycle

A

Ornithine + Carbamoyl Phosphate → Citrulline + Aspartate → Argininosuccinate - Fumarate → Arginine → Urea + Ornithine

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43
Q

Urea Cycle: Mitochondrial Reactions

A

Formation of Carbamoyl Phosphate and Citrulline

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44
Q

Urea Cycle: Cytoplasmic Reactions

A

Synthesis of Arginosuccinate, Cleavage of Arginosuccinate to form Arginine, Arginine cleavage into Urea and Ornithine

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45
Q

Urea Cycle Enzymes: Formation of Carbamoyl Phosphate

A

Carbamoyl Phosphate Synthetase I

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46
Q

Urea Cycle Enzymes: Formation of Citrulline

A

Ornithine Transcarbamoylase

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47
Q

Urea Cycle Enzymes: Synthesis of Arginosuccinate

A

Arginosuccinate Synthetase

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48
Q

Urea Cycle Enzymes: Cleavage of Arginosuccinate to form Arginine

A

Argininosuccinase

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49
Q

Urea Cycle Enzymes: Arginine cleavage into Urea and Ornithine

A

Arginase

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50
Q

Urea Cycle: Substrates

A

NH3, Aspartate, CO2

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51
Q

Urea Cycle: Rate-Limiting Step

A

CO2 + NH3 → Carbamoyl Phosphate

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52
Q

Urea Cycle: Rate-Limiting Enzyme

A

Carbamoyl Phosphate Synthetase I

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53
Q

Urea Cycle: Energy Requirement

A

4 ATP

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54
Q

Urea Cycle: Co-Factors

A

N-acetylglutamate, Biotin

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55
Q

Diffuses from the liver and is transported in the blood to the kidneys where it is filtered and excreted in the urine, a portion diffuses from the blood into the intestines and is cleaved to CO2 and NH3 by bacterial urease

A

Urea

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56
Q

Enzyme defect in the urea cycle, hyperammonemia, elevated blood glutamine, decreased BUN, lethargy, vomiting, hyperventilation, convulsions, cerebral edema, coma, death

A

Hereditary Hyperammonemia

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57
Q

Hereditary Hyperammonemia: Type 1 Defect

A

Carbamoyl Phosphate Synthetase I Deficiency

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58
Q

Hereditary Hyperammonemia: Type 2 Defect

A

Ornithine Transcarbamoylase Deficiency

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59
Q

Hereditary Hyperammonemia: Treatment

A

low protein diet, administration of Na benzoate or phenylpyruvate to capture and excrete excess nitrogen

60
Q

Compromised liver function, tremors, slurring of speech, somnolence, vomiting, cerebral edema, blurring of vision

A

Acquired Hyperammonemia

61
Q

Exclusively ketogenic AAs

A

Leucine, Lysine

62
Q

Ketogenic and Glucogenic AAs

A

Phenylalanine, Tyrosine, Tryptophan, Isoleucine

63
Q

Ketogenic AAs yield

A

acetoacetate, acetyl-CoA/acetoacetyl-CoA

64
Q

Glucogenic AAs yield

A

Pyruvate, intermediates of the Krebs Cycle

65
Q

AAs that enter the Krebs Cycle via α-ketoglutarate

A

Glutamine, Glutamate, Proline, Arginine, Histidine

66
Q

AAs that enter the Krebs Cycle via Pyruvate

A

Alanine, Serine, Glycine, Cysteine, Threonine, Tryptophan

67
Q

AAs that enter the Krebs Cycle via Fumarate

A

Phenylalanine, Tyrosine

68
Q

AAs that enter the Krebs Cycle via Succinyl-CoA

A

Methionine, Valine, Isoleucine, Threonine

69
Q

AAs that enter the Krebs Cycle via Oxaloacetate

A

Aspartate, Asparagine

70
Q

AAs synthesized from transamination of α-ketoacids

A

Alanine, Aspartate, Glutamate

71
Q

AAs synthesized from amidation of Glutamate and Aspartate

A

Glutamine, Asparagine

72
Q

AA synthesized from Glutamate

A

Proline

73
Q

AA synthesized from Methionine and Serine

A

Cysteine

74
Q

AA synthesized from 3-phosphoglycerate

A

Serine

75
Q

AA synthesized from Serine

A

Glycine

76
Q

AA synthesized from Phenylalanine

A

Tyrosine

77
Q

AA synthesized into heme, purines, creatine, conjugated to bile acids

A

Glycine

78
Q

AA synthesized into phospholipid, sphingolipid, purines, thymine

A

Serine

79
Q

AA synthesized into GABA

A

Glutamate

80
Q

AA synthesized into thioethanolamine of CoA, taurine

A

Cysteine

81
Q

AA synthesized into histamine

A

Histidine

82
Q

AA synthesized into creatinine, polyamines, NO

A

Arginine

83
Q

AA synthesized into serotonin, NAD, NADP, melatonin

A

Tryptophan

84
Q

AA synthesized into catecholamine, thyroid hormones (T3 & T4), melanin

A

Tyrosine

85
Q

Deficiency in phenylalanine hydroxylase or tetrahydrobiopterine cofactor, tyrosine becomes essential, phenylalanine builds up, excess phenylketones (phenylacetate, phenyllactate, phenylpyruvate)

A

Phenylketonuria

86
Q

Mental retardation, growth retardation, fair skin, eczema, musty body odor

A

Phenylketonuria

87
Q

Phenylketonuria: Treatment

A

decrease phynylalanine and increase tyrosine in diet

88
Q

Congenital deficiency of homogentistic acid oxidase in the degradative pathway of tyrosine, alkapton bodies cause urine to turn to black on standing, connective tissue is dark (ochronosis), benign, may have debilitating arthralgias, pigmentation of the sclera (Osler’s Sign)

A

Alkaptonuria

89
Q

Congenital deficiency in Tyrosinase or Tyrosine Transporters, lack of melanin leads to increased risk of skin cancer, can result from a lack of migration of neural crest cells

A

Albinism

90
Q

Albinism: inability to synthesize melanin from tyrosine, autosomal recessive

A

Tyrosinase Deficiency

91
Q

Albinism: decreased amounts of tyrosine and thus melanin

A

Defective Tyrosine Transporters

92
Q

Autosomal recessive, cystathionine synthase deficiency, decreased affinity of cystathione synthase for pyridoxal phosphate, homocysteine methyltransferase deficiency, excess homocysteine, cysteine becomes essential

A

Homocystinuria

93
Q

Treatment for cystathionine synthase deficiency

A

decrease methionine, increase cysteine, B6 and folate in the diet

94
Q

Treatment for decreased affinity of cystathione synthase for pyridoxal phosphate

A

increase B6 in the diet

95
Q

Mental retardation, osteoporosis, tall, kyphosis, lens subluxation (downward, inward), atherosclerosis, stroke, MI

A

Homocystinuria

96
Q

Common inherited defect of renal tubular AA transporter for cystine, ornithine, lysine and arginine in the PCT of the kidneys, excess cystine in the urine leads to cystine stones (staghorn calculi)

A

Cystinuria

97
Q

Cystinuria: Treatment

A

Acetazolamide (alkalinize the urine)

98
Q

Kidney Stones in Acidic Urine

A

uric acid, cystine

99
Q

Kidney Stones in Alkaline Urine

A

magnesium alkaline phosphate (struvite) from urease producing bacteria (Proteus)

100
Q

Blocked degradation of branched AA (Valine, Isoleucine, Leucine) due to a deficiency in α-ketoacid dehydrogenase, causes increased α-ketoacid in the blood (esp. leucine), severe CNS defects, mental retardation, death

A

Maple Syrup Urine Disease

101
Q

Cyclic compounds formed from the linkage of four pyrrole rings through methyne (-HC) bridges, form complexes with metal ions bound to nitrogen atom of the pyrrole rings

A

Porphyrins

102
Q

The heme of hemoglobin contains

A

iron

103
Q

The heme of chlorophyll contains

A

magnesium

104
Q

Heme synthesis is present in

A

all tissues

105
Q

Used in hemoglobin, myoglobin, cytochromes, catalase, peroxidase, guanylate cyclase

A

heme

106
Q

The initial and the last three steps in the formation of porphyrins occur in

A

mitochondria

107
Q

The intermediate steps occur in the

A

cytosol

108
Q

Steps in Heme Synthesis

A

Formation of δ-aminolevulinic acid, porphobilinogen, uroporphobilinogen, heme

109
Q

Heme Synthesis: Rate-Limiting Step

A

Glycine + Succinyl CoA → δ-Aminolevulinic Acid

110
Q

Heme Synthesis: Rate-Limiting Enzyme

A

ALA Synthase

111
Q

Heme Synthesis: ALA Synthase Co-Factor

A

Pyridoxine (B6)

112
Q

Heme Synthesis: condensation of two molecules of ALA by zinc-containing ALA Dehydratase, inhibited by heavy metal ions (lead) that replace the zinc

A

Formation of Porphobilinogen

113
Q

Introduction of iron (Fe3+) into protoporphyrin IX occurs spontaneously but the rate is enhanced by ferrochelatase, also inhibited by lead

A

Formation of Heme

114
Q

Genetic or acquired disorders due to abnormalities in the pathway of biosynthesis of heme, erythropoietic or hepatic

A

Porphyrias

115
Q

Most Common Porphyria

A

Porphyria Cutanea Tarda

116
Q

Photosensitivity or chronic inflammation to overt blistering and shearing in sun-exposed areas, abdominal pain (after ring, step 5 onwards), neuropsychiatric symptoms (before ring)

A

Porphyria

117
Q

Pyridoxine deficiency associated with Isoniazid therapy

A

Sideroblastic Anemia (ringed sideroblasts)

118
Q

Heme synthase (ferrochelatase) introduces the Fe2+ into protoporphyrin IX to make the heme ring, microcytic, hypochromic anemia

A

Iron Deficiency

119
Q

Inactivates many enzymes in heme synthesis (ALA dehydratase, ferrochelatase)

A

Lead Poisoning

120
Q

Coarse basophilic stippling of RBC, headache, memory loss, peripheral neuropathy, claw hand, wrist-drop, nausea, abdominal pain, diarrhea, lead lines in gums, deposits in epiphyses, increase urinary ALA and free erythrocyte porphyrin

A

Lead Poisoning

121
Q

Causes microcytic, hypochromic anemia

A

IDA, Thalassemia, Lead Poisoning

122
Q

Causes megaloblastic anemia

A

Folate/B12 Deficiency, Pernicious Anemia

123
Q

Causes normocytic, normochromic anemia

A

blood loss, chronic disease, CKD

124
Q

Causes increased MCHC

A

Hereditary Spherocytosis

125
Q

ALA synthase deficiency, anemia, decreased red cell counts and Hgb

A

X-linked Sideroblastic Anemia

126
Q

Abdominal pain, neuropsychiatric, urinary δ-aminolevulinic acid

A

ALA Dehydratase Deficiency

127
Q

Uroporphyrinogen I synthase deficiency, abdominal pain, neuropsychiatric, urinary porphobilinogen (+), uroporphyrin (+)

A

Acute Intermittent Porphyria

128
Q

Uroporphyrinogen III synthase deficiency, no photosensitivity, urinary porphobilinogen (-), uroporphyrin (+)

A

Congenital Erythropoietic Porphyria

129
Q

Uroporphyrinogen decarboxylase deficiency, photosensitivity, urinary porphobilinogen (-), uroporphyrin (+)

A

Porphyria Cutanea Tarda

130
Q

Coproporphyrinogen oxidase deficiency, photosensitivity, abdominal pain, neuropsychiatric, urinary porphobilinogen (+), uroporphyrin (+), fecal protoporphyrin (+)

A

Hereditary Coproporphyria

131
Q

Protoporphyrinogen oxidase deficiency, photosensitivity, abdominal pain, neuropsychiatric, urinary porphobilinogen (+), fecal protoporphyrin (+)

A

Variegate Porphyria

132
Q

Ferrochelatase deficiency, photosensitivity, fecal protoporphyrin (+), red cell protoporphyrin (+)

A

Protoporphyria

133
Q

After 120 days, RBCs are taken up and degraded by the

A

reticuloendothelial system (liver, spleen)

134
Q

Heme Degradation

A

formation of bilirubin → uptake of bilirubin by the liver → formation of bilirubin diclucoronide → secretion of bilirubin into bile → formation of urobilins in the intestine

135
Q

Reactions of heme oxygenase in reticuloendothelial cells

A

heme → biliverdin (green) → bilirubin (red orange)

136
Q

Bilirubin transported to the liver by binding to

A

albumin

137
Q

In the liver, bilirubin binds to intracellular proteins particularly

A

ligandin

138
Q

Bilirubin is conjugated to two molecules of glucuronic acid by

A

Bilirubin Glucuronyltransferase

139
Q

Bilirubin Glucuronyltransferase Deficiency

A

Crigler-Najjar I and II, Gilbert Syndrome

140
Q

Transported into the bile canaliculi and then into the bile, susceptible to impairment in liver disease

A

Bilirubin Diglucuronide

141
Q

In the gut, bilirubin is converted into a colorless substance

A

urobilinogen

142
Q

Intestinal bacteria oxidize urobilinogen into

A

stercobilin (brown)

143
Q

Some urobilinogen is reabsorbed from the blood and enters the

A

portal circulation

144
Q

Remaining urobilinogen is transported by the blood to the kidney where it is converted to

A

urobilin (yellow)

145
Q

Jaundice: hemolytic anemias, neonatal physiologic jaundice, Crigler-Najjar I and II, Gilbert syndrome, toxic hyperbilirubinemia

A

Unconjugated Hyperbilirubinemia

146
Q

Jaundice: biliary tree obstruction, Dubin-Johnson syndrome, Rotor Syndrome

A

Conjugated Hyperbilirubinemia

147
Q

Used to measure total and direct bilirubin

A

Van den Bergh Reaction

Jaspie - Biochemistry II (15 decks)

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