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20 Cards in this Set
- Front
- Back
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What happens if a person doesn't maintain nitrogen balance?
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They start to catabolize muscle.
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Where does digestion of dietary proteins begin?
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Stomach
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Which enzymes play a role in degrading proteins in the stomach?
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pepsin, rennin
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Which endopeptidase is specific for for aromatic or dicarboxylic amino acids?
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Pepsin
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What is the action of rennin in protein digestion?
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Rennin - Slows release of proteins from stomach for more complete digestion by pepsin
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How are AA's transported post digestion?
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Transported via diffusion, facilitated diffusion, or active transport, depending on the amino acid
Also, there are several Na+-dependent amino acid transport systems for L-amino acids or small peptides. |
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What is Cystinuria? and what is it characterized by?
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It is a transport defect(intestinal and renal) for cystine and other dibasic amino acids(lysine, arginine, ornithine).
It is characterized by the presence of cystine-containing calculi, or stones in the kidney, bladder, ureter. |
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What are the clinical manifestations of Cystinuria?
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The presence of cystine calculi results in hematuria (which is blood in the urine) and dysuria (which is pain on urination), urinary tract infections, and flank pain. Eventually, cystinuria can lead to renal failure.
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What is happening at the molecular level in Cystinuria?
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There are defects of the heterodimeric dibasic amino acid transporter rBAT.
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The treatments for cystinuria are based on reducing the concentration of cystine in the urine. How can they be achieved?
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Increase fluid intake (> 4 L/day)
Increase cystine solubility with increased pH (acid pH of the urine promotes cystine insolubility) Maintain low sodium (high sodium increases urinary amino acid excretion in cystinuria patients) and low methionine diet Increase cystine solubility with penicillamine |
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How does penicillimine act in the treatment of Cystinuria?
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Penicillamine forms a mixed disulfide with cysteine, increasing its solubility
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What is Hartnup's Disease?
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Hartnup disease is caused by a defect in the transport of neutral amino acids.
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What is Hartnup's Disease characterized by?
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Intermittent cerebellar ataxia
Pellagra-like symptoms:dermatitis, dementia & diarrhea. |
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What is the pathogenesis of Hartnup's Disease?
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Failure to absorb tryptophan, which is an essential amino acid and precursor for nicotinamide, serotonin.
The deficiency in tryptophan, leads to decreased nicotinimide which results in the pellagra-like symptoms. Also the decreased serotonin (neurotransmitter) can account for the neurologic symptoms. |
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What is the treatment of Hartnup's Disease?
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Nicotinamide supplementation (40-200 mg/day) along with a high protein diet (including tryptophan).
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After removal of the Amino group during AA catabolism what can the carbon skeleton be used for?
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Carbon backbone undergoes conversion to compounds used for gluconeogenesis or the generation of ATP.
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What is the first step in AA metabolism? and how can it be achieved?
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The first step in the metabolism of amino acids is the removal of nitrogen. In most amino acids, this occurs by transamination. Some amino acids are deaminated to yield ammonia directly.
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What is the co-factor used by aminotransferases? and what is it derived from?
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Pyridoxal phosphate (PLP) derived from Vitamin B6 (pyridoxine)
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What is the action of PLP as a cofactor to aminotransferases?
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The aldehyde group on PLP enters into a Schiff base linkage with the e-amino group of a lysine residue at the active site of the aminotransferase. When the amino acid substrate comes along, it’s a-amino group displaces the active site lysine and forms a Schiff base linkage with PLP. The characteristics of the Schiff base linkage allow the transfer of electrons between different atoms, and allows the hydrolysis and transfer of the nitrogen to PLP.
The N-containing PLP then forms a Schiff base linkage with an a-keto acid, and the reverse happens, with the subsequent transfer of the nitrogen to form a new a-amino acid (usually glutamate). |
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Discuss the Transamination of a Non-Essential Amino Acid.
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In the transamination reaction, the amino group of one amino acid is transferred to an a--keto acid to create a different amino acid. Glutamate is always involved in the transamination reaction, because it is able to donate the nitrogen to the urea cycle, as you will see.
For the non-essential amino acids, this reaction is reversible if, for example, alanine is limiting. Thus, non-essential amino acids are also synthesized from a-keto acid precursors. |
