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102611 Amino Acid Metabolism
UC MED 2015
79
Medical
Graduate
10/27/2011

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Term
What are the essential amino acids?
Definition
-L-Leucine
-I-Isoleucine
-V-Valine
-T-Threonine
-M-Methionine
-F-Phenylalanine
-W-Tryptophan
-R-Arginine(children)
-K-Lysine
-H-Histidine
Term
What are the strictly ketogenic amino acids?
Definition
L-leucine
K-Lysine
Term
What are the ketogenic amino acids, but can also be glucogenic?
Definition
I-isoleucine
T-Threonine
F-Phenylalanine
Y-Tyrosine
W-Trytophan
Term
What is released in the stomach that is important to protein digestion and absorption?
Definition
HCl and pepsinogen

acidic conditions allow pepsinogen to undergo self-proteolysis, releasing PEPSIN
Term
Where is pepsin found and what does it cleave?
Definition
In stomach, cleaves proteins after R groups that are...
-hydrophobic(F,Y)
-acidic(D,E)
Term
What does the pancreas secrete in the small intestines?
Definition
1) Bicarbonate
2) Trypsinogen
3) Chymotrypsinogen
4) Proelastase
5) Procarboxypeptidase
Term
What is the role of Bicarbonate?
Definition
neutralize stomach acid
Term
If there is inappropriate activation of one of the pancreatic enzymes, what results?
Definition
pancreatitis
Term
What catalyzes the conversion of trysinogen to trypsin? Where is this enzyme found?
Definition
Enteropeptidase(also called enterokinase)
It is found on the brush border of the intestinal epithelium cells(enterocytes)
Term
What does trypsin do?
Definition
It activates the other pancreatic enzymes...
chymotrypsin
elastase
carboxypeptidase
Term
Which amino acid dimer will be formed from digestion?
Definition
Cys-Cys(no enzyme to break or digest)
Term
What is Cystinuria?
Definition
-Results from defect in transport of cystine, lysine, arginine, and ornithine
-Problem manifest in kidney(poor reabsorption from glomerular filtrate) and intestinal(poor absorption from diet) membranes
-Cystine accumulates in urine;relatively insoluble; stones develop
-NO amino acid deficiencies seen
Term
What is Hartnup's disease?
Definition
-Defect in transport of NEUTRAL amino acids (I,L,F,T,W,V)
-affects both intestine and kidneys
-most pressing problem is lack of W(if Niacin low, trouble making NAD+)
-Pellagra like symptoms occur(diarrhea, dermatitis, dementis)

-TREAT with supplemental W and Niacin
Term
What precursor can be synthesized to make glutamate, then it can be reprocessed to make Glutamine, Proline, and Arginine?
Definition
alpha-ketoglutarate
Term
What precursor can be used to make aspartate, which can be modified to make asparagine?
Definition
Oxaloacetate(OAA)
Term
What precursor can make serine then modified to make cysteine and glycine?
Definition
3-phosphoglycerate
Term
What precursor is used to make Tyrosine?
Definition
Phenylalanine
Term
What precursor can be used to make Alanine?
Definition
Pyruvate
Term
B6 is the precursor for what important cofactor?
Definition
pyridoxal phosphate
Term
What type of reactions is B6 or pyridoxal phosphate required?
Definition
1) Transaminations
2) Racemizations (D to L configuration)
3) ß-elimination reactions
4) ß-addition reactions
5) gamma-eliminations
Term
What are the 3 reactions that can fix free ammonia?
Definition
1) glutamine synthetase
2) glutamate dehydrogenase
3) CPS-I
Term
Glutamine is made from NH3, ATP, and Glutamic acid using?
Definition
Glutamine Synthetase
Term
Asparagine is made from Asp, ATP, and Gln as a nitrogen donor using what?
Definition
Asparagine Synthetase
Term
What enzyme makes Gly from Ser? Is there any necessary cofactors?
Definition
Serine Hydroxymethyl Transferase

requires- THF
Term
What degradative reactions require THF?
Definition
1) Serine (uses N5, N10 methylene THF)
2) Formate (N10 formyl THF)
3) Histidine degrastion (N5 formimino THF)
4) Glycine cleavage enzyme(N5,N10 methylene THF)
Term
What Biosynthetic reactions require THF?
Definition
1) dUMP to TMP (N5,N10 methylene)
2) Glycine to serine (N5,N10 methylene)
3) Homocysteine to methionine (N5 methyl THF)
4) Purine biosynthesis (N10 formyl)
Term
What are the methyl donors in biochemistry?
Definition
1) N5-Methyltetrahydrofolate-only used in conversion of homocysteine to methionine
2) SAM (S-Adenosylmethionine)-used for all other methyl transfer reactions- Product is S-adenosylhomocysteine,
which then makes homocysteine
Term
What enzyme will make Tyr from Phe? What cofaactors are needed if any?
Definition
Phenylalanine Hydroxylase

requires THB(tetrahydrobiopterin)
Term
After Tyr synthesis, what is needed to regenerate THB?
Definition
NADPH, THB needs to be reduced
Term
Cysteine is derived from?
Definition
Methionine
Term
What enzyme is necessary for Cysteine biosynthesis?
Definition
B6
Term
What two reactions is B12 required for?
Definition
1) L-methylmalonyl CoA to succinyl CoA
2) Homocysteine to methionine(regenerates THF)
Term
If B12 is not activated, what disease will result?
Definition
Megoblastic anemia; neurological symptoms
Term
Amino Acid Biosynthesis is mostly regulated by?
Definition
feedback inhibition of branch pathways
Term
All amino acids are degraded to one of seven family members, what are these?
Definition
1) Acetoacetyl-CoA
2) Acetyl-CoA
3) Pyruvate
4) alpha-ketoglutarate
5) Succinyl-CoA
6) Fumarate
7) Oxaloacetate
Term
What four disorders result from defects in Phe degradation?
Definition
1) PKU
2) Alcaptonuria
3) Tyrosinemia, type 1
4) Tyrosinemia, type 2
Term
Alcaptonuria
Definition
Buildup- of homegentisic acid in urine

Signs- black urine, may lead to arthritis
Term
PKU (Phenylketonuria)
Definition
Two types
-Classical-missing Phenylalanine hydroxylase
-missing ability to make or regenerate THB

Buildup- Phenylpyruvate (TA of phe) and Phe

Symptoms-neuronal damage, mental retardation

Treat-restricted Phe diet
Term
If you put a pt w/ PKU on a proper diet and they still have symptoms then?
Definition
They probably have a problem with THB.

So keep restricted PHE diet
-supplement with DOPA, 5-hydroxytryptophan, THB
Term
Tyrosinemia I
Definition
lacks- fumarylacetoacetate hydrolase

symptoms- vomiting, failure to thrive, cabbage-like odor, liver failure, early death in accute form
Term
Tyrosinemia II
Definition
Defect in tyrosine aminotransferase (tat)

Symptoms- skin and eye lesions, neurological problems

Treat- low phe and tyr diet
Term
Homocysteinemia/uria
Definition
Lacks-
1) methionine synthase
2) N5,N10-methyl tetrahydrofolate reductase
3) Cystathionine-ß-synthase

Causes- elevated levels of homocysteine and methionine in the blood and urine

Symptoms- dislocation of optic lens, osteoporosis, mental retardation(poss elevated risk for heart disease)

Treatment-(only effective if enzyme has reduced affinity for these)
1) B6 effective in lowering homeocysteine 50% of cases
2) B12
3) Folic Acid
Term
What does homocysteine do?
Definition
-It inhibits endothelial cell growth and promotes smooth cell proliferation. (This exacerbates the problems of atherosclerosis.
-Blocks the action of an inhibitor of the coagulation cascade; thus coagulation is poorly controlled, clots can form, and thrombosis results. (deep vein thrombosis is common in these pts)
Term
Taking what pre-conceptually reduces the risk of neural tube defects?
Definition
folic acid
Term
What does extra folic acid do?
Definition
A common mutation in humans is a temperature-sensitive N5, N10 methylene tetrahydrofolate reductase (the enzyme which makes N5-methyl THF). With too little N5-methyl THF, homocysteine accumulates. Overcome by taking folic acid;increases substrate levels such that sufficient N5-methyl THF can be made
Term
What produces B12 and how can we obtain it?
Definition
produced by bacteria, obtained in milk, meat
Term
What leads to pernicious anemia?
Definition
Lack of intrinsic factor that is secreted by the stomach. This factor binds to B12, so it is able to be transported into the intestinal epithelial cells.
Term
What does B12 have that is similar to a porphyrin ring?
Definition
corrin ring complexed with cobalt atom
Term
What two enzymes are important in B12 processing, if this doesn't occur vitamin deficiency will occur?
Definition
1) Methyl-cobalamin-used to transfer methyl group from N5-methyl THF to homocysteine
2) Adenyl-cobalamin-used in the conversion of methyl-malonyl-CoA to succinyl-Coa
Term
Both B12 and Folic Acid deficiencies lead to?
Definition
megaloblastic anemia
Term
B12 deficiency also leads to?
Definition
neurological problems-tingling in extremities, mental status changes; folate deficiency does not cause this
Term
Why do neurological problems happen with B12 deficiency?
Definition
Lack of SAM-leads to hypomethylation in the brain(altering of gene expression, myelin sheath formation)
Term
What pathway is in the liver so hypomethylation does not occur there?
Definition
betaine pathway(trimethylglycine)
Term
Lack of what enzyme cause Maple Syrup Urine Disease?
Definition
The alpha-ketoacid dehydrogenase is defective. this enzyme catalyzes the decarboxylation of all three amino acids, leucine, isoleucine, and valine
Term
What three amino acids are affected in maple syrup urine disease?
Definition
leucine, isoleucine, valine
Term
Where is the primary site of branched chain AA metabolism?
Definition
muscle; liver has low levels (of the alpha-ketoacid DH) which catalyzes oxidative carboxylation
Term
What are the symptoms of Maple Syrup Urine Disease?

Poss. treatments?
Definition
ketoacidosis and mental retardation

Some respond to thiamin(B1)-required for oxidative carboxylation

dietary restriction of branched chain AA, not effective since they are essential
Term
Heme is what type of ring? What is heme synthesized from?
Definition
-porphyrin ring

-synthesized from succinyl-CoA and glycine
Term
The corrnin ring is found in what? What is it synthesized from?
Definition
B12, synthesized from succinyl-CoA and glycine in non-mammalian systems, hence why we need to obtain in our diet from meats, or fortified cereals
Term
What is the rate limiting step in heme synthesis?
Definition
∂-aminolevulinic acid synthase
Term
What does ∂-aminolevulinic acid synthase do?
Where does this rxn happen?
Definition
Take succinyl-CoA and glycine and makes ∂-aminolevulinic acid.

Occurs in the mitochondria, product leaves and then pathwat ontinnues in the cytosol
Term
What is the inhibitor of ∂-aminolevulinic acid synthase?
Definition
heme
Term
What happens in lead poisoning?
Definition
1) lead inhibits ∂-aminolevulinic acid dehydratase
2) ∂-aminolevulinic acid accumulates and is secreted in the urine
3) heme levels are very low
4) anemia results
Term
What does ∂-aminolevulinc acid dehydratase do?
Definition
It is a condensation rxn, that takes 2 ∂-aminolevulinc acids and makes porphobilinogen
Term
Four porphobilinogen condense to form?
Definition
tetrapyrrole
Term
The linear tetrapyrrole cyclizes to make?
Definition
uroporphyriogen III, goes on to make heme or vit B12
Term
In general terms, defects in heme biosynthesis are known as?
Definition
porphyrias
Term
If a precursor has a double bond(in this case for porphyrias), exposure to what is no good?
Definition
UV light- creates radical intermediates which react with O2 to create superoxide, which damages and destroys skin cells (this is because our skin cells are exposed to the most UV light)
Term
Since our test is on Halloween, where does Liebermann think the vampire legend came from?
Definition
Pts with porphyrias(heme sensitive), person is photopobic andand needs to replenish heme by eating very rare(bloody) meats.
Term
Where does heme degradation normally occur?
Definition
spleen
Term
Heme is broken down into?
Definition
Bilirubin
Term
Jaundice results from?
Definition
buildup of bilirubin

-results from enhanced red cell destruction
-liver damage
-immature conjugation system
Term
What happens to bilirubin in the liver?
Definition
conjugated to glucuronic acid-enhances its solubility

(newborns sometimes have an immature conjugation system, leading to neonatal jaundice)
Term
What is necessary in heme degradation?
Definition
NADPH
Term
What are they aspects of regulation of amino acid degradation(4)?
Definition
1) substrate availability
-a-Km for aa-tRNA synthetase is lower than Km for aa degradation
-b-high levels of aa will at least start degradative pathway
2) there is feedback inhibition(never learned anything specific)
3) enzymes levels regulated(partly from our diet)
4) Nitrogen flow is regulated by Glutamate dehydrogenase and glutamine synthetase
Term
What is the role of alanine amino acid degradation?
Definition
1) proteins are degraded for energy
2) free NH3s result
3) glutamate DH fixes NH3 into glutamate
4) alpha-ketoglutarate and pyruvate undergo a transamination rxn in the muscle creating glutamate and alanine.
5) Alanine flows through our blood til it reaches our liver
6) Alanine undergoes reverse of the transamination rxn producing pyruvate and Glutamate
7) Glutamate is reacted on by Glutamate DH and free NH3 is fixed into uric acid from the urea acid cycle
Term
What are the various roles of Glutamine(depends on tissue needs)?
Definition
1) fuel for intestine, kidney, and immune system
2) removes ammonia from the nervous system
3) kidney uses ammonium ion to buffer urine
Term
What are the major gluconeogenic substrates?
Definition
amino acids
Term
What type of amino acids are predominantly used as fuels?
Definition
BCAA (branched chain aa)
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