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35 Cards in this Set
- Front
- Back
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Nitrogen Cycle |
-all organisms convert NH3 to organic nitrogen -only bacteria can fix nitrogen -generally animals not able to convert nitrate-> ammonia -dietary source (mainly protein) -loss > intake= negative N balance -loss < intake= positive N balance |
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Diet |
Protein-> amino acid-> tissue protein or non protein nitrogen derivatives -> carbohydrates -> amino nitrogen in glutamate ->acetyl COA-> TCA cycle-> 2x CO2 |
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Essential and Non essential |
Essential: isoleucine, lysine, leucine, methionine, phenylalanine, threonine, tryptophan, valine Non Essential: alanine, asparagine, aspartate, cysteine, glutamine, glutamate, glycine, hydroxyproline, hydroxylysine, proline, serine, tyrosine |
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Amino Acid Requirements (Humans) |
Semi essenital: arginine and histidine. Needed extra in pregnancy |
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Glutamate Synthesis |
a-ketoglutarate-> glutamate via. glutamate dehydrogenase (allosteric control) via. GTP/ATP or GDP/ADP |
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Glutamine Synthesis |
glutamate <=> glutamine via.glutamine synthetase (forwards) glutaminase (reverse) |
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Alanine Synthesis |
pyruvate->alanine via. glutamate + transaminases to convert to aKG |
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Aspartate Synthesis |
oxaloacetate-> aspartate via. glutamate+ transaminases to convert to aKG |
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Transamination |
-catalysed by transaminases or amino transferases -universal: glu->aKG, ala-> pyruvate |
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Asparagine Synthesis |
aspartate<=>asparagine via. asparagine synthetase (forwards) asparaginase (reverse) |
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Serine |
3 phosphoglycerate->serine->glycine via. hydroxymethyl transferase |
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Proline |
Glutamate->Proline (complex reaction) cofactos: aKG, ascorbic acid, Fe Proline-> 4 hydroxyproline. happens in collagen |
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Tyrosine: not made de novo |
Phenylalanine-> Tyrosine via. phenylalanine hydroxylase also needs tetra h-biopterin-> H biopterin (generates OH needed on tyrosine |
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Cysteine Synthesis: not made denovo |
Methionine+ Serine-> cystathionine-> aketo butyrate + cysteine |
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Interorgan Exchange |
-muscle generates 50% total pool AA's -mostly Glutamine & Alanine to blood -in liver, glucose production from alanine higher than other AA's -branched chain AA's (essential ie. isolecuine and valine) -in fasting state, provide brain with energy source -fed state: extracted by muscle as liver does not utilise -communication muscle and liver=> alanine |
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AA Catabolism |
-pyridoxal required ->transaminations/deaminations ->decarboxylations ->threonine aldolase activity -active form pyridoxal phosphate -1-2% body protein turned over daily (1/4 excreted as urea) -20-25% ends up in urea, rest recylced -no storage facility for excess AA's, therefore constant requirement -all have a function |
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AA Metabolism |
Diet-> Amino Acid Pool Can be made into: -creatine -purine/pyrimidine -neurotransmittors -AA hormones (ie. thyroid) -NH to urea to urin Amino acid pool to Common metabolic Pool via transamination, amination and deamination |
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General Reactions AA's |
-transamination -deamination -racemisation -decarboxylation |
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Histidine Catabolism |
Histidine->Histidase -degraded to glutamate -tetrahydrafolate needed to degrade histidine -must have folate, if not intermediate in blood |
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Decarboxylation |
Histidine->Histamine via. histidine decarboxylase -tyrosine->tyramine bacterial: aged cheese, wine, beer, pickled herring, chicken, overripe avocados, soy (more tyramine) -release of norepinephrine/octapamine granules -MAO normally breaks down -MAO inhibtors allow more tyramine to enter -ingestion of tyramine containing food leads to severe hypertensive response |
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Deaminations |
-oxidative -amino acids to a keto acid -occurs through combined action of transaminations and glutamate dehydrogenase -only in glutamate does oxidative deamination occur quickly |
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Ultimate Fate of AA |
-transamination followed by deamination 1. amino acid-> a keto acid 2. a keto glutarate-> glutamate via glutamate dehydrogenase NH->glutamine and urea |
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Urea Cycle |
-ammonia toxic -synthesized in liver (all enzymes present) -transported to kidney for excretion -arginase responsible for cyclic nature of pathway -use 3 ATP for each urea generated -Humans: 90% urinary nitrogen is urea, rest creatinine and uric acid -n-acetyl glutamate must be present -carbomoyl phosphate synthase 1 (in mitochondria) -Co2+NH2-> carbamoyl phosphate -balance-> glutamate -deaminate to release 1st NH -transaminase NH to aspartate -form N-acetylglutamate -precursor for glutamine (keeps ammonia in system) -also part of glutathione and GABA |
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Urea Cycle |
Carbamoyl Phosphate (in mitochondria) + Ornithine (In cytoplasm, transported into mito via ornithine transcarbomoylase)=> Citrulline -Citrulline + Aspartate-> arginosuccinate via. arginosuccinate synthetase ->arginine and fumerate (to malate) or oxaloacetate (back to aspartate via. transamination) Arginine-> arginase to urea and ornithine |
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Ureotelic Enzymes |
-main source: liver -small amount arginase in kidney and brain -2 metabolic fates for carbamoyl phosphate 1. urea synth in mitochondria 2. pyrimidine synth in cytoplasm Carbamoyl phosphate->carbamoyl aspartate -> pyrimidine or to citrulline and urea |
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Urea Cycle Disorders |
-carbomoyl phosphate synthase I defiency: TOXIC: hyperammonaemia type1 -ornithine transcarbomoylase deficiency: hyperammonaemia 2 -citrullinaemia: inc. citrulline CSF, urine and plasma -arginosuccinic aciduria: no arginosuccinate lyase, inc. in CSF, urine and blood -hyperarginaemia: inc. CSF & blood, low erythrocyte arginase -common symptoms are ammonia intoxication, respiratory alkalosis and mental impairment |
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Creatine |
-glycine, lysine + methionine-> gluandinoacetate + ornithine-> creatine -> creatine phosphate (for energy) -> creatine -creatine phosphate is a source of high energy P when ATP limited -in muscle, brain and blood -excrete 2g/d, creatinine almost totally by renal -enzymes for synth of creatine in liver and pancreas -site of synth, removed from that of utilisation -creatinine clearance used as measure of glomerular filtration rate -prediction of drug dosage |
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AA metabolism Disorders |
-PKU: phenylalanine hydroxylase defect: phe->tyr -phe is transaminated instead to phenylactate, phenylactate and phenylpyruvate excreted 1-2g/d -metnal retardation -2% carriers -rarer form: dihyrdobiopterin reductase defiency -lipophilic: diffuse into brain, interfere, mental retardation |
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Other Disorders |
Maple Syrup Urine Disease: branched chain a-keo acid dehydrogenase complex -remove branch chain amino acid from diet Histidinaemia: histidase deficiency, spleen defects, some mental retardation Hemocystinuria: cystathione B synthase deficiency, mental retardation, eye disease, osteoporosis, faulty bone structure. Some respond to pyridoxine |
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Other Disorders: |
Glycinuria: urinary glycine, renal tube defect, kidney stones Hyperoxaluria: cant breakdown glycoxylate, urine oxalate formed, oxalate renal stones, very severe, frequent UTI, renl failure |
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Other Disorders |
Alkaptonuria: homogentisate oxidase deficiency blocks production of maleyacetoacetate -homogentistic acid in urine, darkens on standing -deposits cause skin to darken -arthritis can develop later in life Albinism: tyrosine hydroxylase/tyrosinase absent -tyrosine blocked to dopa and dopaquinone (->melanin) -melanins are polymers of these later catabolites -white hair, pink skin, photophobia |
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Noradrenaline & Adrenaline |
Tyrosine hydroxylase->Dopa->Dopa decarboxylase->dopamine->dopamine B-oxidase->noradrenaline->adrenaline |
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Serotonin |
-vasoconstrictor and smooth muscle stimulation (tryptophan->serotonin) -sleep inducing -locations: intestinal walls: likely excitatory neurotransmitter -blood: platelets uptake from plasma (active transport) & released at site of tissue damage -CNS: many functions, deficiency related to depression -hence, drugs that maintain brain levels of 5-HT used as anti depressants |
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Thyroid Hormones |
-monoiodothyroxine->diiodotyrosine-> triiodothyroxine-> thyroxine |
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Glycogenic/Ketogenic aa |
glutamate: arg, pro, his, gln A-ketoglutarate-> succinyl COA: ile,met,val Fumarate: try, phe Oxaloacetate-> aspartate: asn Acetoacetyl COA: leu, trp, lys, tyr, phe-> acetyl COA: ile, leu, trp ->Citrate pyruvate-> acetyl COA: ala, cys, ser, gly, thr |
