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100 Cards in this Set

  • Front
  • Back
4 Pathways that amino acid degradation products can participate in:
-TCA cycle
-Fatty acid synthesis
-Metabolism to ketone bodies
At what 6 molecules do AA's enter the TCA?
1. Pyruvate
2. AcCoA
3. a-Ketoglutarate
4. Succinyl-CoA
5. Fumarate
6. Oxaloacetate
What amino acids can directly enter the TCA cycle at Pyruvate?
Cys Gly
Ser Thr
What enters the TCA cycle at pyruvate indirectly?
Tryptophan, via Alanine
What amino acids enter the TCA cycle at AcCoA? (5)
What amino acids enter the TCA at a-Ketoglutarate?
(all the above contribute to)
What 4 amino acids enter the TCA at Succinyl-CoA?
What amino acids enter the TCA at Fumarate?
Where else do Phe/Tyr enter TCA?
So Phe/Tyr enter the TCA at what 2 molecules?
AcCoA + Fumarate
What enters the TCA at OAA?
Asparagine --> Aspartate
At what 2 sites of the TCA does Threonine enter?
What does the enzyme Asparaginase do?
Converts Asparagine to Aspartate
What is important about Asparaginase?
Used as anti-leukemia chemotherapy agent
How is Asparaginase an anti-leukemic agent?
It degrades Asparagine which is necessary for leukemic cell growth.
What can Aspartate be degraded to?
Oxaloacetate or Fumarate
What enzyme will convert Aspartate to OAA? Cofactor?
Aspartate Aminotransferase (AST)
-Cofactor is PLP
-Concomitantly converts a-KG to Glutamate.
What are the 3 alternatives to Aspartate in its degradation?
-Make OAA
-Make Fumarate via Urea cycle
-Make Alanine via Nitric Oxide synthesis (via citrulline)
How exactly is Aspartate used in the urea cycle?
In step 2b - It replaces the AMP in Citrullyl-AMP to make Argininosuccinate.
How is Fumarate made in the urea cycle?
By Argininosuccinate lyase - produces Fumarate + Arginine
What is essential to remember about the production of Citrullyl-AMP in the Urea cycle?
It requires 1 ATP
How are Arginine and Proline degraded to a-ketoglutarate?
Both converted to common Glutamate y-semialdehyde; this gets converted to Glutamate, then a-KG
What enzymes convert Arginine to y-semialdehyde?
-Ornithine d-aminotransferase
What is important about arginase?
It is the same enzyme as used in the urea cycle.
What is important about Ornithine d-aminotransferase?
It transfers the DELTA amino group from ornithine to glutamate.
What is EXTREMELY IMPORTANT about the enzyme that converts Glutamate y-semialdehyde to Glutamate?
Ornithine d-aminotransferase deficiency causes:
Gyrate atrophy
How is Histidine converted to Glutamate?
By release of NH4+, incorporation of 2 H2O, and addition of H4-Folate.
What products are formed by conversion of His to Glutamate?
Where does N5Formamino,H4Folate go?
It donates a carbon to the one carbon pathway.
How is Glutamine converted to Glutamate?
By Glutaminase
What is a byproduct of the Glutaminase reaction?
Where does the ammonia produced by Glutaminase go?
To make Carbamyl Phosphate in the urea cycle.
How is Ammonia useful?
It neutralizes organic acids in the kidney.
How is Glutamate converted to a-ketoglutarate?
By one of 2 processes:
-Glutamate dehydrogenase, or
-Aminotransferase to a-KG
How does metabolism of Gly, Ser, Thr, Cys, Trp, and Ala occur?
Thr -> 2-Amino-3-ketobutyrate -> Gly -> Ser -> Pyruvate

Trp -> Ala -> Pyruvate
What is the important thing to remember about Threonine in this pathway?
It is its secondary pathway - not the most prominent.
How does Alanine get to Pyruvate?
Alanine Aminotransferase (a-KG to glutamate)
How does Cysteine get to pyruvate?
Loses a sulfur via 2 steps
Where does pyruvate go after being made from these AA's?
To oxaloacetate to fuel gluconeogeneis or AcCoA for FA synthesis or TCA cycle.
How does the breakdown of Ser and Gly differ from the mechanisms of Ala, Trp, Cys, and Met?
Ser and Gly can EITHER go to PYRUVATE or to CO2+NH4+
What enzyme takes Ser to Pyruvate?
Serine dehydratase
What are the 2 alternative fates of Serine?
-Direct breakdown to Pyruvate
-Conversion back to Glucose, to donate 1-C units to that pathwy.
What enzyme catalyzes conversion between Ser and Gly?
Serine hydroxymethyl transferase
What is required by the enzyme Serine Hydroxymethyl Transferase?
-N5,N10-methylene H4Folate
What enzme allows for donation of 1-C units from Glycine? What products are generated?
Glycine Cleavage enzyme; generates NH4+ and CO2
What enzyme is Glycine cleavage enzyme similar to?
PDH - contains TPP, Lipoamide, and FAD
What does deficiency in Glycine cleavage enzyme result in?
Nonketotic Hyperglycemia
What is the common name for H4 Folate?
Why is Tetrahydrofolate important?
It can't be made in the body - must be taken in from the diet.
What pathway is Folate involved in?
the Folate One-Carbon pathway
What is the function of tetrahydrofolate?
It acts as a one-carbon carrier
What is the active portion of Tetrahydrofolate that changes in the folate pathway?
What are the 3 components of Tetrahydrofolate?
Which 4 amino acids donate 1-carbon units to the One Carbon Pathway?
-Serine (MAJOR)
Difference between dTMP and dUMP:
one carbon
In the one-carbon pathway, which molecule is
-Most oxidized?
-Least oxidized?
Most = N5-methyltetrahydrofolate

Least= N5-formyltetrahydrofolate
What AA makes N5-formiminotetrahydrofolate?
What AA makes N5-methyltetrahydrofolate?
Ser and Gly
What is the purpose of the One Carbon Pathway?
To make purines for DNA/RNA synthesis - essential for life.
Exactly what compounds are purines synthesized from?
N10-Formyl Tetrahydrofolate & N5N10-Methenyl-tetrahydrofolate.
What is the N5-methyltetrahydrofolate used for?
To make Methionine via Methionine synthase
What is an alternate use of N5N10-Methenyl-tetrahydrofolate rather than purine synthesis?
Synthesis of dTMP from dUMP
What molecule receives the one-carbon unit to make Methionine?
What enzyme catalyzes formation of Methionine?
Methionine synthase
What cofactor is required by Methionine synthase?
Vitamin B12
So what can Vit B12 deficiency or Methionine Synthase deficiency result in?
Folate trapping - not regenerated by methionine synthesis!
What is the result of folate deficiency?
Spina bifida and neural tube defects in fetuses of mothers deficient in folate.
What conditions are associated with elevated Homocysteine levels?
-Cardiovascular disease
3 vitamin cofactors used by the Sam-E one-carbon pathway?
Vit B12
What is the strange thing about Methionine SYNTHESIS?
There is NO NET SYNTHESIS - it keeps getting shuttled through the Sam-E one carbon cycle.
What are 6 things made by methylation from SAM-E?
-Methylated DNA
-Capped mRNA
What 3 cofactors are needed in the Sam-E one-carbon pathway?
-Vit B12
What happens if Methionine is in EXCESS, or Vit b12, folate, or methionine synthase are deficient?
Methionine will be degraded by the Sam-E cycle.
How can the Sam-E cycle DEGRADE methionine? Its whole purpose is to keep it going and recycled!
It degrades homocysteine instead b/c the enzyme methionine synthase won't work on it.
How is Homocysteine degraded?
By breakdown to Cystathionine, then to a-Ketobutyrate
What enzymes break down homocysteine? What are their cofactors?
Cystathionine b-Synthase (PLP)
Cystathionine y-Lyase (PLP)
What byproduct is made in homocysteine breakdown?
What diseases are associated with elevated Homocysteine or slightly decreased Cystathionine B-synthase levels?
-Cardiovascular disease
-Alzheimer's disease
What results from FRANK (severe) deficiency of the b-synthase?
Severe symptoms similar to marfan's.
What else could cause increased homocysteine levels?
PLP deficiency (cofactor for the b-synthase enzyme)
What would decreased y-lyase levels result in?
Where does the a-Ketobutyrate from Methionine degradation (homocysteine degradation) go?
To be converted to Propionyl-CoA (along with 3 other AA's)
What 4 amino acids are converted to Propionyl-CoA? Then what?
Thr, Ile, Met, and Val
Then they convert to SuccinylCoA
What intermediate is common to Methionine and Threonine breakdown?
What enzyme makes a-Ketobutyrate from Threonine?
Threonine dehydratase (this is its primary pathway, not threonine dehydrogenase)
What happens to Val and Ile as they are converted to Propionyl CoA?
Val loses 2 CO2
Ile loses 1 CO2 + 1 AcCoA
What pathway is the degradation of Branched Chain Amino Acids similar to?
Fatty acid metabolism
What 2 enzymes are used in degrading Val, Ile, and Leu?
1. Branched Chain Aminotrnsfrase
2. Branched Chain a-Ketoacid Dehydrogenase Complex
What does Branched Chain aminotransferase do? Cofactor?
Removes the NH3 from the AA backbone from Val/Ile/Leu - makes a-ketoacids.
Cofactor = PLP
What does Branched chain a-ketoacid dehydrogenase complex do?
Converts the a-ketoacids to AcylCoA derivatives via NAD+
What 2 branched chain AA's go on to propionyl CoA?
Val and Ile
Why is Br. Chain A-Ketoacid Dehydrogenase Complex important to know about?
Because its deficiency causes MAPLE SYRUP URINE DISEASE (MSUD)
What is the Br. Chain A-Ketoacid Dehydrogenase Complex identical to?
What population is MSUD frequency extremely high in?
Pennsylvania Mennonites - 1/176
What is the treatment for MSUD?
Long term protein diet restriction
How is PropionylCoA converted to Succinyl CoA?
By the same reaction used in odd chain FA degradation!!
What is the intermediate produced in PropionylCoA convrsn to Succinyl CoA? What is added?
HCO3 addition makes Methylmalonyl CoA
What enzyme converts Methylmalonyl CoA to Succinyl CoA? What is its cofactor?
Methylmalonyl CoA mutase
Cofactor = Coenzyme Vit B12
What is associated with deficiency of Vit B12 or Methylmalonyl CoA mutase?
Methylmalonic Aciduria