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59 Cards in this Set

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  • Back
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Is tyrosine an essential amino acid?
No, but it is derived from phenylalanine, which is an essential amino acid
Which amino acid are derived from oxaloacetate in a transamination, PLP rxn?

Which amino acid can be derived from that transamination?
(a) Asparate

(b) Asparagine
How is Asp related to Asn?

Which 2 enzymes makes this possible?
Asparagine is derived by the addition of an amine group: which requires: Aspartate, Glutamate, ATP and Asparagine synthetase

The reverse rxn produces Aspartate from Asparagine, required: Asparagine, asparaginase and H2O
None
(a) Which amino acids are related to ∂-KG?

(b) Which is the central amino acid that links all these amino acids?
a) Glu, Gln, proline, arginine, histidine…

b) glutamate
How is proline linked to glutamate?
glutamate <-> gluamate semialdehyde <-> pyrroline 5-carboxylate <-> proline
a) What form of energy and what reducing agent are required in the formation of proline from glutamate.

b) at which stage of the glutamate to proline pathway is energy needed?

c) at which which points in the rxn is a reduciing agent needed?

d) what is need to produce Glutamate from Proline?
a) ATP and NADPH…

b) glutamate <-> glutamate semialdehyde.

c) Glutamate --> Glutamate semialdehyde and Pyrroline 5-carboxylate --> proline (both require NADPH)

d) an oxidizing agent to reverse the rxn: proline --> pyrroline 5-carboxylate requires FAD+) and glutamate semialdehyde --> glutamate (requires NAD+)
Besides proline, which amino acid is glutamate semialdehyde a precursor to?
arginine
None
How is arginine linked to glutamate?

How is this different from the urea cycle?
1. glutamate <-> gluamate semialdehyde <-> ornithine <-> arginine

2. The formation of arginine from ornithine occurs in the liver as a means of eliminating excess Nitrogen. To produce arginine from glutamate requires the cooperative actions of the intestinal and kidney cells.
How do the intestine and the kidney work together to form arginine from ornithine?

Name the requried enzymes
a) the intestines have the enzyme that convert glutamate --> ornithine --> citruline…

b) the citrulline is passed through the blood stream to the kidneys

c) the kidneys have the enzyme (arginase) that convert citrulline to arginine
None
Why is it that the arginine made in the liver, as part of the urea cycle, is not useful?
because of the large amount of arginase in the liver, the produced arginine would be broken down into ornithine as a means to eliminate unwanted nitrogen… thus arginine in the circulation is produced by the intestines and the kidneys where the product (arginine) is not converted to ornithine.
How is Histidine synthesized from glutamate?
Tt's not, it an essential amino acid. However, Glutamate is synthesized from Histidine.
None
Glutamate and histidine are related to each other (Histidine ->->-> glutamate) but glutamate has 5 carbons, where histidine has 6 carbons. What happens to the other carbon?
the extra carbon is transferred to THF (which binds 1-carbon units)
None
What are the four amino acids related to ∂-KG (glutamate)?
arginine, histine, Gln, proline
Can humans synthesize phenyl rings?
no
Which amino acids have phenyl rings?
phenylalanine, tryptophan, and tyrosine
Why is tyrosine not an essential amino acid?
tyrosine is synthesized from phenylalanine
Phenyl ring amino acids can be degraded to fumarate and acetoacetate. Given this fact, are phenyl ring amino acids (tyrosine, phenylalanine, and tryptophane) glucogenic or ketogenic?
Both: phenyl ring amino acids are ketogenic via acetoacetate and glucogenic via fumarate
None
(a) Which enzyme and cofactor are required for the conversion of phenylalanine to tyrosine?

(b) What can inhibit the production of tyrosine?
(a) phenylalanine hydrolase (adds an -OH group) and tetrahydrobiopterin (BH4)

(b) the lack of the above
What two cofactors contain a pterin ring?
BH4 (or THB) and THF
Can humans synthesize BH4 (tetrahydrobiopterin)?
yes, from GTP
Can humans synthesize THF?
no
What is BH4, which is needed in the conversion of Phe to Tyr, made from?
GTP
(a) What does BH4 converted back and forth from and to?

(b) What is needed in this conversion?
(a) BH4 <-> BH2

(b) A reducing agent, NADH, and an oxidizing agent O2 --> H2O
What amino acid degradation occurs in tandem with the BH4 to BH2 rxn?
Phe to Tyr
a) What is needed to convert BH2 back to BH4?

b) Is energy required and in what form?
a) dihydrobiopterin reductase…

b) a reducing agent ,NADH
What are the 3 causes of PKU (Hint: phenylketonuria is an excess of Phe in the urine)
a) defective enzymes in the GTP >>> BH4 synthesis…

b) defect in phenylalanine hydrolase (which is the enzyme that drives the Phe to Tyr rxn)…

c) defect in the dihyropteridine reductase... (or lack of NADH)
what was the first inborn error of the metabolism linked directly to an enzyme deficiency?
PKU related to a deficiency of phenylalanine hydrolase (PAH)
None
the phenoketone, phenylpyruvate, is elevated in PKU due to transamination from phenylalanine and is the classical method of diagnosis. What is really causing the problem in PKU?
elevated levels of phenylalanine
How is PKU diagnosed?
fluormetry or bacterial inhibition assay
What type of inheritance is PKU attributed to?
autosomal recessive
What is the dietary restriction for people with PKU?
500-600 mg Phe/day
What are the IQ effects of treating and untreating PKU on individuals?
untreated 1% IQ>70… treated normal IQ >90%
What impact does aspartame have on people with PKU
aspartame is catalized to produce aspartate, phenylalanine and methanol, thus people with PKU are increasing their intake of phenylalanine
None
What is the concern for PKU-moms?
If they don't watch their diets, the fetus can suffer elevated blood levels of phenylalanine (not urinary phenylketones) which has teratogenic effects… even if the child is heterozygous… ALSO, too little Phe will have an effect on biosynthesis
None
What is Tryptophan synthesized from in the body?

What is produced in the degradation of Trp?
It's not, it's an essential AA

Formate (a 1-carbon unit, taken up by THF), alanine, acetyl CoA, and Nicotinamide (NAD and NADP... although most is obtained in the diet)
None
a) What are the 3 amino acids branched chain amino acids (BCAA)? b) Are these amino acids essential or nonessential?
a) Val, Ile, Leu… b) all three are essential
None
Of the BCAA, which are glucogenic and which are ketogenic?
Leu is ketogenic (producing acetoacetate) , Val and Ile are glucogenic (producting propionyl CoA, which leads to succinyl CoA in the TCA cycle)
What are the 3 reactions associated with BCAA degradation?

Which branched amino acid, (leucine, valine, or isoleucine), produce a ketone?
1. transamination, oxidative decarboxylation, dehydrogenation

2. leucine --> acetoacetyl CoA
None
a) What is the first step in BCAA degradation and why doesn't occur in the liver? b) Why is this important?
a) Deamination, the liver lacks the needed transaminases… b) BCAAs are the major source of energy for some tissue.
what % of the essential amino acids do BCAA account for?
35-40%
What are the 3 common steps in BCAA degradation?
Transaminase converts BCAA to an ∂-keto acid… b) oxidative decarboxylation converts ∂-keto acid to a CoA-thioester by BCKA dehydrogenase… c) CoA-thioester is the dehydrogenated
None
BCKA dehydrogenase is seen in the third step of Branched Chain Amino Acid metabolism, which 2 other enzymes is the BCKA dehydrogenase enzyme similar to ?
pyruvate dehydrogenase and ∂-KG dehydrogenase (which converts ∂-KG to succinyl CoA
None
What are the steps of the BCKA dehydrogenase enzyme complex?
1) decarboxylation (attatchment of the ∂-KA to Thiamine PPi)…

2) transfer of the fragment to lipoamide to form a thioester…

3) Transfer of the acyl group to CoA and release of this molecule from the enzyme…

4) regeneration of the oxidized lipoamide by the reduction of FAD by dihydrolipoyl DH...

5) oxidation of FADH2 by the reduction of NAD+
None
What is the first step in the BCKA dehydrogenase reaction catalyzed by? And what is it composed of?
E1 = subunit ∂ an ß
What is the term for the mutation in BCKA dehydrogenase and what does it mean?
Y393N: it means that a mutation on the E1∂ subunit has replaced asparagine with a tyrosine.
What is the lay term for Y393N mutation and what are the clinical manifestations?

What is the Rx for this disease?
Maple syrup disease, it is fatal if low BCAA diet is not observed… Seen in "Old Mennonite" and Amish population of SE Penn.

Low dietary intake of BCAA
None
Which amino acids are associated with glycolytic intermediates?
Alanine, Serine, Glycine
Are the amino acids associated with the glycolytic pathway essesntial?
No
1. Summarize how serine can be synthesized in the glycolytic pathway and how it can enter the glycolytic pathway.

2. What regulates the synthesis of serine?
Glycine <-> Serine from a 3-phosphoglycerate intemediate->

Serine -> can re-enter the glycolytic pathway via by first being metabolized to 2-phosphoglycerate

2. What regulates the synthesis of serine? serine does... negative feedback at the level of 3-phosphoglycerate rxn level.
None
1. How are Serine and Glycine related?

2. Besides hyrdroxymethyltransferase, what is needed to catalyze the rxn serine <-> glycine?

3. How many carbons do serine and glycine have?

4. what happens to the extra carbon atom?

5. What is an alternative method for glycine catabolism?
1. Serine/threonine hydroxymethyltransferase rxn.

2. PLP

3. Serine =3C... Glycine = 2C

4. THF transfers the extra carbon to a 1-carbon unit

5. What is an alternative method for glycine catabolism? Glycine cleavage system: D-Amino acid oxidase (which releases NH4)
None
What is the major source of 1-unit carbons?
serine
How are serine and glycine related? (hint: which enzyme) What is also required in this rxn?
a) serine/threonine hydroxymethyltransferase… b) PLP
Show the pathway that links serine and threonine to glycine.
serine <-> glycine <- threonine
None
Serine has 3-carbons and glycine has 2-carbons, what happens to the extra carbon in the serine/threonine hydroxymethyltransferase rxn?
THF will either donate or receive it
PKU is caused by an unstable or absent PAH enzyme, or it is caused by a defective regeneration of THB by dihydrobipterin, or by a defective THB synthesis. If THB synthesis is defective, what is the treatment?
administer THB
What are some proposed causes of neural abnormalities seen in PKUics?
a) deficient tyrosine in the brain… b) high phenylalanine levels alter distribution of metabolites… c) direct effects of phenylalanine
When is the best time to check for PKU?
1-6 weeks after birth
What are the first two steps in BCAA catabolism?
BCAA transaminase ... BCKA dehydrogenase
(a) Which enzyme is deficient in maple syrup disease?

(b) ∂-KA dehydrogenases are much like pyrvate dehydrogenase, such that they are complexes, In maple syrup disease, what is the mutation that causes the disorder and at what part of the BCKA dehydrogenase complex?

(c) What is the role of the part of the complex?

(c) Biochemically, what is observed?
(a) BCKA dehydrogenase

(b) Try is replaced by Asp on E1 part of complex.

(c) the decarbosylation and covalent bodn to thiamine pyrophosphate)

(d) rise in BCAA (Val, Leu, Iso)