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16 Cards in this Set
- Front
- Back
Various aspects of amino acids |
-Position of -NH2 α-AA (in proteins), b-AA (b-alanine), γ-AA (GABA) ... etc. -Configuration on C* L-amino acids (most) ´ D-amino acids (? unknown function) -Acide-base properties „amino-acidic“ (15) ´ acidic (2) ´ basic (3) -Side chain character non-polar (9) ´ polar (6) ´ ionized (5) -Availability for humans essential (9) ´ semiessential (3) ´ non-essential (11) -Metabolism glucogenic (13) ´ ketogenic (2) ´ mixed (5) -Occurence in proteins proteinogenic (20) ´ non-proteinogenic (e.g. ornithine, homocysteine) |
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Three sources of AA pool: |
1)Proteolysis of dietary proteins(food) 2)Proteolysis of tissue proteins (physiological turnover,more in starvation) 3)Synthesis of non-essential AA(11) |
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Three utilizations of AA pool: |
1)Synthesis of tissue and bloodplasmaproteins (liver) 2)Synthesis of low-molecular nitrogen compounds (with specific functions) 3)Catabolism: deamination + utilization of carbonskeleton |
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Three utilizations of AA carbon skeleton |
1)Gluconeogenesis(in starvation,most AA are glucogenic) 2)Synthesis of FAand TAG (inAA excess) 3)Metabolic fuel = gain of energy(minor utilization) |
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Transcellular transport of AA from intestine to portal blood |
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Various aspects of amino acids |
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Endogenous proteins have different biological half-lives > |
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Degradation of proteins in lysosomes |
•doesnot require ATP, non-specific•extracellularand membraneproteins•long-livedintracellular proteins •extracellularglycoproteins – sialic acid at terminal position on oligosaccharide chain isremoved = asialoglycoproteins – they are recognized by liver receptors --> degradationin liver lysosomes |
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Proteins in nutrition |
•daily intake of proteins for adult 0.8 g/kg•four main sources: meat, eggs, dairy products, beans•intake ofanimal and plant proteins should be balanced•animalproteins contain moresulfur AA –more acidifying•proteinquality depends on content of essencial AA, theirratio, and protein digestibility•generally:animal proteins have higher quality thanplant proteins•wheat –deficitof Lys,Trp, Thr, Met•beans –deficitof Met, CyslP |
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Transamination |
•mostAA (not Lys, Thr, Pro, His, Trp, Arg, Met) •aminogroup is transferred from AA to 2-oxoglutarate •cofactor– pyridoxal phosphate (® Schiff bases) •reversible reaction Þimportant for synthesis of AA |
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Glutamate dehydrogenase (GMD, GD, GDH) |
•requirespyridine cofactorNAD(P)+ •GMDreaction is reversible •dehydrogenation ofCH-NH2 to imino group C=NH •hydrolysisof imino group to oxo group and ammonia •allosteric regulation: GTP,ATP, NADH inhibit, ADP activates, •low energy level incell is the signal for production of 2-oxoglutarate and its oxidation |
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Two main sources of ammonia in organism |
1.Deamination of glutamate (GD reaction) in tissues,mainly inliver and kidneys 2.Bacterial putrefaction of proteins in the large intestine produces nitrogen catabolites(e.g. amines + ammonia), ammoniadiffuses freely into portal blood Þ portalblood has high concentration of NH4+ Þ eliminated by liver |
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Production of ammonia in the body -overview |
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Compare: Ammonium ions in body fluids |
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Acide-base properties of NH3 |
pKB (NH3) = 4.75 (weak base) NH3 + H2O ⇄ NH4+ + OH- pKA (NH4+) = 14 – 4.75 = 9.25 (very weak acid) under physiological pH values inICF and ECF (~ 7.40): 98% NH4+ 2 % NH3 |
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Threeways of ammonia detoxification |
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