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69 Cards in this Set
- Front
- Back
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Why is vitamin B6 needed for amino acid metabolism?
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Pyridoxal Phosphate (PLP) is used as a co-enzyme for most amino acid reactions; PLP is derived from B6
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The cofactor BH4 is needed for what type of amino acid reactions?
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ring hydroxylations (phenylalanine to tyrosine)
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The cofactor FH4 is needed for what purpose in amino acid synthesis/degradation?
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transfer carbon groups at various oxidation states
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How many essential amino acids are there?
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9 out of 20; they must come from diet since they are not made by our body
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How many amino acids can be synthesized by the body (non-essential)?
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11/20
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In a starvation state, why do we want to break down proteins and amino acids?
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the carbons of amino acids can be used to make glucose and CO2
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In a non-starvation state, what happens to amino acid carbon products?
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they are stored as glycogens and triacylglycerols like glucose and fatty acids
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What are glucogenic amino acids?
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their metabolic products can be used to create glucose
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What are ketogenic amino acids?
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their metabolic products can be used to create acetyl CoA or acetoacetate
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4 amino acids synthesized from intermediates of glycolysis?
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serine, glycine, cysteine, alanine
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How is PKU tested in newborns right after birth?
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Guthrie assay; B. subtillis is plated with B-thienylalanine (an inhibitor of B. subtillis growth) and the newborns blood. phenylalanine is needed for B. subtillis growth so if it grows, there is enough phenylalanine in the baby's blood to counteract the B-theinylalanine's inhibitory effects
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Pyruvate can become which amino acid by the actions of ALT
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alanine (ALT = alanine aminotransferase in liver)
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Serine is formed from which intermediate of glycolysis?
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3-phosphoglycerate
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A defect in phosphoserine phosphatase will lead to an accumulation of what compound?
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3-phospho-L-serine or 3-phosphoglycerate
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A defect in phosphoserine phosphatase will lead to a decrease in which amino acid?
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serine
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Serine has a negative feedback loop for its own production. High levels of serine have what effect on its synthesis?
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high serine levels down-regulate 3-phosphoglycerate dehydrogenase. 3PGD (intermediate of glycolysis) is now not able to become serine
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An accumulation of what compound can lead to oxaluria type I?
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oxalate; low glyoxalate transaminase = high glyoxalate/low glycine = high oxalate = kidney stones
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What amino acid can be degraded to form glycine?
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threonine; serine also mostly forms glycine, but this is reversible (so its not a degradation of serine)
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Why might high levels of D-amino acid oxidase lead to trouble in a patient?
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D-amino acid oxidase converts glycine into glyoxalate which can become oxalate. oxalate can precipitate in the kidney tubules = stones
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Serine can become cystathione (precursor to cysteine) by combining with what compound?
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homocysteine (from methionine); uses cystathione synthase
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What enzyme converts cystathione into cysteine?
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cystathionase
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High levels of cysteine will down regulate which enzyme as part of a negative feedback loop?
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high cysteine downregulates cystathione synthase
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If cysteine levels are high from the diet, which amino acid is not needed in the production of cysteine?
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methionine is now "spared"; it is doesn't need to give up its sulfur group for cysteine synthesis since we are now getting it from the diet
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Cysteine is broken down into what 2 major molecules?
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Sulfuric acid or PAPS (used in GAGs)
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A defect in which enzyme can directly lead to homocysteinemia (high homocysteine in blood)?
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cystathione synthase
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Pyruvate becomes alanine by what reaction?
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transamination by ALT (alanine aminotransaminase) in liver
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Cystathionuria can be caused by low levels of what enzyme?
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cystathionase (or vitamine B6 since PLP is also needed and PLP comes from B6)
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What commonly causes cystinuria?
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inability to reabsorb cystine in kidneys = stays in tubular fluid. can lead to stones since its insoluble
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Why might patients with cystinosis be more susceptible to infections?
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cystinosis = accumulation of cystine in lysosome = crystals form = damaged lysosomes = less ability to degrade bacterial infections
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4 amino acids that can be made from the TCA cycle intermediate: a-ketoglutarate
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glutamate, glutamine, proline, arginine
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Cells use glutathione for what processes in the cell?
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protect against oxidative damage (GSG:GSSG ratio)
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Glutamine is derived from which amino acid?
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glutamate; uses glutamine synthase
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Glutamate + ______ = glutamine
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NH4+; uses glutamine synthase
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Glutamine can become glutamate by what enzyme?
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glutaminase
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What does homocyst(e)ine refer to?
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to indicate levels of homocystine and homocystiene together
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What is the structural difference between homocystine and homocystiene?
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homocystine = 2 molecules of homocysteine with disulfide bridge
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A defect in what enzymes could lead to homocystinuria?
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cystathione synthase; maybe even cystathionase
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The ammonia released by conversion of glutamine to glutamate can be used by what system?
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kidneys can use it to compensate for respiratory acidosis (i.e. excrete acids in urine)
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Glutamate becomes _______ before becoming proline.
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glutamate semialdehyde
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Hydroxy-proline can only be formed when proline is incorporated with which structure?
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collagen
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How does glutamate semialdehyde lead to arginine formation?
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glutamate semialdehyde is transaminated to form orinthine; ornithine enters the urea cycle and the urea cycle produces arginine
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Glutamate comes from what TCA cycle intermediate?
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a-ketoglutarate
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Arginine can become ornithine with what enzyme?
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Arginase
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How does histidine lead to glutamate formation?
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forms FIGLU which breaksdown into glutamate (and FH4, NH4 etc.)
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How does glutamate semialdehyde become pyrroline-5-carboxyate (leading to proline formation)?
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spontaneous cylcization
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Aspartate and asparagine are derived from what intermediate of the TCA cycle?
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oxaloacetate
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How does oxaloacetate become aspartate?
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transamination
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How does aspartate become asparagine?
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asparagine synthase (and glutamine for the nitrogen group)
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How does asparagine become aspartate?
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asparaginase (releases NH4+)
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3 amino acids that can form fumarate
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aspartate, phenylalanine, tyrosine
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4 amino acids that form Succinyl CoA
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methionine, threonine, valine, isoleucine
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How do high methionine levels lead to high succinyl CoA levels?
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high methionine = high cystathione = high a-ketobuyrate. a-ketobutyrate forms propionyl CoA which become succinyl CoA
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How do high threonine levels lead to high succinyl CoA levels?
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threonine is degraded into a-ketobutyrate = propionyl CoA = succinyl CoA
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What cells carry out most oxidation of branched amino acids?
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muscle cells; these give high energy
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Maple syrup urine disease can be caused by a defect in the breakdown of what amino acids?
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valine, isoleucine, leucine
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A thiamine deficiency will lead to an accumulation of what compounds in blood?
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a-ketoacids from valine, isoleucine, leucine degradation = keto-acidosis
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Is valine glucogenic or ketogenic?
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glucogenic (valine leads to propionyl CoA = succinyl CoA = gluconeogenesis)
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Is isoleucine glucogenic or ketogenic?
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both (Propionyl CoA = gluconeogenesis, and the Acetyl CoA = acetate = ketones)
(Propionyl CoA can lead to succinyl CoA which leads to gluconeogenesis) (acetyl CoA can also lead to acetate formation) |
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Is leucine glucogenic or ketogenic?
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ketogenic (leucine leads to acetoacetate= ketones)
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Are phenylalanine and tyrosine glucogenic or ketogenic?
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both
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Is lysine glucogenic or ketogenic?
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ketogenic
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Tyrosinemia type II is caused by a defect in what enzyme?
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tyrosine aminotransferase; tyrosine build-up, low homogentisic acid
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Alcptonuria results in high levels of what compound?
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homogentisic acid; defect in homogentisate oxidase
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classic PKU is caused by a defect in what enzyme?
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phenylalanine hydroxylase
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Tryoptophan is both a glucogenic and ketogenic AA. It is ketogenic because it produces Acetyl CoA. Why is it glucogenic?
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can be converted into alanine = pyruvate (alanine is easily converted into pyruvate)= glucose (pyruvate = glucose by glucoenogenesis)
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A defect in DHPR can lead to what disorder?
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PKU
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A defect in DHPR will lead to low levels of what compounds?
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BH4, then therefore tyrosine since BH4 is needed to convert phenylalanine into tyrosine
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What causes pellagra?
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low tryptophan/niacin
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Presence of Xanthurenic acid in urine suggest what problem?
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B6 or kynurenine hydroxylase deficiency. PLP (from B6) is needed to convert kynurenine into alanine. build-up of kynurenine = Xanthurenic acid in urine
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