Amino Acids/ Nitrogen Metabolism Flashcards

Terms Definitions
Name the essential/required amino acids
1. Arginine
2. Histidine
3. Isoleucine
4. Leucine
5. Lysine
6. Methionine
7. Phenylalanine
8. Threonine
9. Tryptophan
10. Valine
How many amino acids are essential/non-essential?
There are 10 essential and 10 non-essential
But Tyrosine might be an exception.
What is an essential/non-essential amino acid?
Essential means that it needs to be part of the diet.
***What is the metabolic fate of excess dietary amino acids, and where does NH3 come from?
Excess dietary amino acids cannot be stored for future use, nor are they excreted unused. Instead, they are converted to common metabolic intermediates that can either be oxidized by the TCA cycle or used to form glucose.
Since humans consume 100 g of protein per day. To maintain Nitrogen balance, the body must dispose of 14 g of excess Nitrogen per day. That will be in the form of urea
x catalyze the transfer of an alpha-amino groups from an alpha-amino acid to an alpha keto acid
Aminotransferases
Aminotransferases
also called transaminases, generally transfer alpha-amino groups from a variety of amino acids to alpha-ketoglutarate to yield glutamate plus an alpha keto acid. Can run the reverse reaction too.
How does the glutamate dehydrogenase reaction relate to the urea cycle?
This reaction occurs in the mitochondrial matrix, and produces free ammonium. Free ammonium, which is toxic, is sequestered in the mitochondrial matrix, and the ammonium may be taken up to enter the urea cycle.
Function of the urea cycle
to dispose of ammonium and bicarbonate, and synthesize arginine.
The product of urea/urea cycle occurs in the
liver
Consuming 100g of protein per day, to maintain Nitrogen balance, the body must dispose of x grams of excess nitrogen per day
14
Where do the atoms of urea come from?
The N and C atoms composing urea come from NH4+, HCO3-, and the alpha NH2 groups of aspartate.
Why is Glutamine (Gln) important in nucleic acid biosynthesis?
Glutamine is a major N donor in the biosynthesis of many organic N compounds such as purines, pyrimidines, and other amino acids.
This enzyme catalyzes the ATP-dependent amidation of the y-carboxyl group of glutamate to form glutamine
glutamine synthetase
Glutamate dependent transamination of alpha-keto acid carbon skeletons is a primary mechanism for
amino acid synthesis
A primary mechanism for amino acid synthesis
Glutamate dependent transamination of alpha-keto acid carbon skeletons
Deficiency of vitamin B6 causes what?
Rare. Patients with Vitamin B6 deficiency have dermatitis, somnolence, and confusion.
Vitamin B6 deficiency alone is uncommon, usually other vitamins are lacking too. Elderly and alcoholics have an increased risk of vitamin B6 deficiency.
Is pyridoxal, pyridoxol, pyridoxamine found in plants or animals?
Pyridoxal and pyridoxamine are found in animals, while pyridoxol is found in plants and sold commercially.
The active form of vitamin B6 is
Pyridoxal-5-Phosphate or PLP
PLP
Pyridoxal-5-Phosphate, the active coenzyme form of vitamin B6.
The x group of PLP is reactive
The carbonyl group of PLP is reactive
PLP acts by forming a x with amino acids
stable Schiff base
Rearrangement to a Schiff base with the arriving substrate is a x reaction
transaldiminization reaction
x reactions involve cleavage of bonds to an amino acid
PLP
The transamination of oxaloacetate by glutamate to yield aspartate and alpha-ketoglutarate is a prime example of
glutamate dependent transamination that utilizes PLP as a coenzyme.
This reaction is important for the biosynthesis of aspartate
The transamination of oxaloacetate by glutamate to yield aspartate and alpha-ketoglutarate is a prime example of glutamate dependent transamination that utilizes PLP as a coenzyme.
Cause, consequences, and treatment of homocystinuria and hyperhomocysteinemia
Homocystinuria
- A rare inherited disease that results in very high levels of homocysteine in the bloodstream. High levels of homocysteine in the blood damage blood vessels. Untreated children will have cardiovascular problems. Treat it with vitamin B6 supplements, trimethylglycine, and/or decreased methionine in the diet.
Trimethylglycine/Vitamin B6 may help convert homocysteine to Met.
*HOMOCYSTEINE IS AN INTERMEDIATE IN THE SYNTHESIS OF METHIONINE FROM ASPARTATE!
Hyperhomocysteinemia - less severe disorder.
Adults with high levels of homocysteine in the blood may be at higher risk of heart attack and stroke. Eating folic acid, the vitamin form of the coenzyme THF, may reduce blood levels of homocysteine to safe levels.
*****Metabolic degradation of the common amino acids.
What does glucogenic and ketogenic mean?
What is the fate and classification of the following amino acids,
Ile
Val
Phe
Tyr
Amino acids that give rise to precursors for glucose synthesis like alpha ketoglutarate, succinyl CoA, fumarate, oxaloacetate, and pyruvate - are termed glucogenic
Those that are degraded to acetyl CoA or acetoacetate are called ketogenic because they can be converted to fatty acids or ketone bodies.
Ile - Both, glucogenic-succinyl CoA, ketogenic- acetyl CoA
Val - Only glucogenic - succinyl CoA
Phe - Both, glucogenic - Fumarate, ketogenic - Acetoacetate
Tyr - Both, glucogenic-Fumarate, ketogenic - Acetoacetate
What intermediates of metabolism are entry points for ketogenic amino acids?
acetoacetate and acetyl CoA
What intermediates of metabolism are entry points for glucogenic amino acids?
Alpha-ketoglutarate, succinyl CoA, fumarate, oxaloacetate, pyruvate
Maple syrup urine disease, cause/consequences/treatment
Key intermediate?
1. Cause - maple syrup urine disease is a hereditary defect in the oxidative decarboxylation of branched chain keto-acid intermediates. This defect leads to elevated levels of valine, leucine, and isoleucine (and their corresponding branched chain alphaketo acid) in the blood and urine. The urine of these individuals smells like maple syrup. Readily detected in newborn urine screening.
Can cause mental and physical retardation and death if untreated.
Treat with strict dietary restriction of Leu, Val, and Ile
In the reaction - valine and isoleucine are converted to succinyl CoA, with propionyl CoA as an intermediate.
Alkaptonuria-
cause, effects, treatment
Key intermediate?
Alkaptonuria is a human genetic disease arising from a defect in TYROSINE DEGRADATION. DEFICIENCY IN HOMOGENTISATE DIOXYGENASE. Patients with alkaptonuria excrete in the urine large amounts of homogentisate, which oxidizes in air to TURN BLACK! BLACK PISS. Patients with this disease have a tendency to arthritis later in life. Treat by restricting dietary Phe and Tyr
Know that homogentisate and 4-maleyl-acetoacetate are along the pathway of tyrosine degradation, with ACETOACETATE and Fumarate AS END PRODUCTS.
Phenylketonuria-
What is it? Main reaction?
Phenylalanine is converted to TYROSINE by phenylalanine hydroxylase. Phenylketonuriacs don't have enough phenylalanine hydroxylase and accumulate excess phenylalanine, which accumulates and is converted to phenyl pyruvate. If untreated, possible severe mental retardation.
Treat by diet low in phenylalanine.
Phenylalanine is converted to TYROSINE by
phenylalanine hydroxylase
What causes the accumulation of phenylpyruvate
excess phenylalanine that can't be converted to tyrosine
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