QTR 2 Block 3 Biochemistry: Amino Acid Metabolism and Special Products Flashcards
Name the essential amino acids.
Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, MEthionine, Histidine, Arginine, Leucine, Lysine ( PVT TIM HALL)
What is a transamination reaction?
Reaction involved in synthesis or degradation of AA involving transfer of amine groups…usually involves alphaketoglutarate and glutamate
Transaminases require what B vitamin derivative as a prosthetic group?
Pyridoxal Phosphate ( Vit B6 derivative)
What two AA are NOT substrates for reversible transamination reactions?
Lysine and Threonine
Amino acid metabolism is heavily dependent on coenzymes derived from what?
Vitmine B6, B 12, Folate, Biotin, and Niacin
What does it mean for an AA to be glycogenic or ketogenic?
These are AA whose carbon skeleton can be converted into glucose or ketones with the help of transaminase reactions.
Where do the carbon skeletons of non-essential AA come from in the body?
mainly derived from energy metabolism intermediates or certain essential AA
What TCA intermediates can provide carbon skeletons for glycogenic or ketogenic processes?
alphaketoglutarate and oxaloacetate
What glycolytic intermediates can provide carbon skeletons for glycogenic or ketogenic processes?
3- phosphoglycerate and pyruvate
Which essential amino acids can provide carbon skeletons for non essential amino acids and ketogenic or glycogenic synthesis?
tyrosine and cysteine
A transaminase reaction of this AA can produce pyruvate, and is quantitatively the most important glycogenic AA. What other amino acid is transaminated in this way?
Alanine Transaminase (ALT) - requires alphaketoglutarate and glutamate. Aspartate also uses this mechanism.
How do alphaketoglutarate and glutamate participate in transamination reactions?
alphaketoglutarate picks up an extra amine group from the AA being transaminated/deaminated, and forms glutamate.
Asparagine uses ______ as an NH3 donor in its transamination.
Glutamine
Propionyl CoA can be metabolized to __________, with the help of what two coenzymes?
Succinyl CoA; Biotin and Vitamin B12
What are the glycogenic/ketogenic properties of the branched chain amino acids leucine, valine, and isoleucine?
Valine is Glycogenic, Leucine is Ketogenic, and Isoleucine is both
How can the non-essential AA serine be synthesized in the body?
It can be formed from 3-phosphoglycerate (from glycolysis) via oxidation, transamination, and removal of the phosphate by a phosphatase
How is serine converted to pyruvate?
via deamination and dehydration by Serine (Threonine) Dehydratase
How is glycine formed from serine?
via “one carbon metabolism” by Tetrahydrofolate (THF) and using serine hydroxymethyl transferase
Is serine glycogenic?
YUUP.
By what two pathways is threonine catabolized?
It basically has three pathways, and is catabolized in a glycogenic manner to propionyl coA and pyruvate, or in a ketogenic manner to acetyl coA.
The major route in threonine catabolism involves what enzyme?
Threonine Dehydrogenase
Glycine may be synthesized from what sources?
serine and THF, threonine, and Co2 + NH4 + methylene THF
Glycine is catabolized mainly by ______.
serine hydroxymethyl transferase to serine, and glycine decarboxylase
Since glycine may be converted to serine it is considered to be _______.
Glycogenic
Why is Tetrahydrofolate (THF) important in one carbon metabolism?
it serves to transfer one carbon units in a number of reactions
The net synthesis AND catabolism of glutamine, proline and arginine share what intermediate compound?
Glutamate
Catabolism of histidine to glutamate will form what biproduct?
N5-formimino THF
What is the importance of glutamine in maintenance of blood nitrogen levels?
it serves as a non-toxic carrier of NH4 produced by other reactions- it then transfers these carrier NH4 groups to other tissues for the formation of purines for example, and also supplies the bulk of excreted ammonia from the kidneys ( due to glutaminase activity)
Cysteine can be synthesized from _____ and _____, and depends on the availability of what other AA?
homosysteine plus serine…depends on the availability of methionine
The major route of cysteine catabolism is through oxidation by _________.
Cysteine Dioxygenase….cysteine is considered glycogenic.
Essentially all of the phenylalanine carbon skeleton NOT used for protein synthesis is converted to _______ by what enzyme?
tyrosine; phenylalanine hydroxylase
Why is tyrosine not considered an essential amino acid?
it can be formed by the remnants of phenylalanine
This enzyme is inducible by high concentrations of tyrosine and glucocorticoid hormones.
Tyrosine Aminotransferase (TAT)
What are the important products formed by catabolism of tryptophan?
Alanine, quinolinic acid, and acetyl coA ( therefore tryptophan is both glycogenic and ketogenic
This initial enzyme in the tryptophan catalysis pathway is inducible by high concentrations of tryptophan and by glucocorticoid hormones.
Tryptophan Oxygenase
Lysine catabolism forms _______.
Acetoacetyl Coa (Ketogenic)
This AA disorder involving a deficiency in phenylalanine hydroxylase will result in ____.
Phenylketonuria (PKU) …phenylpyruvate is excreted in large quantities
This disorder can cause a loss of 50 IQ points in the first year of life and is the one of the most prevalent aminoacidopathies.
Phenylketonuria
What is the treatment for PKU? What implication does this have for female PKU patients of child bearing age?
A diet low in PKU, also a supplementation with oral THB for PKU pts with biopterin defect. Female PKU patients not on dietary management have a 90-97% change of bearing mentally retarded offspring, so should be on a Phe restricted diet prior to planned pregnancy
This aminoacidopathy results in opacity of the cornea, skin lesions, and variable degrees of mental retardation in some patients.
Tyrosinemia Type 2 ( aka Richner-Hanhart Syndrome)
This benign aminoacidopathy results secondary to delayed activity in p-hydroxyphenylpyruvate oxidase.
Neonatal Tyrosinemia
This historically important disorder results in the passing of black urine, secondary to a homogentisate oxidase deficiency.
Alcaptonuria
This disorder results in liver failure, renal failure, and painful neurologic symptoms. Due to a deficiency of fumarylacetoacetate hydrolase.
Tyrosinemia Type I
This disorder results in sweet scented urine due to a branched alpha ketoacid dehydrogenase deficiency, also neurological symptoms and shortened life expectancy. More prevalent in mennonite populations.
Maple Syrup Urine Disease (MSUD)
What special AA products function as coenzymes for other reactions?
SAM, NAD, Coenzyme A and Carnitine
Where does the Sulfur atom in CoA-SH come from?
Cysteine
Catecholamines are derived from what AA??
tyrosine (requires tetrahydrobiopterin /THB)
What AA is used to make acetylcholine?
serine…requires three methyl groups from SAM, and an acetyl group from Acetyl CoA
What important neurotransmitters are considered AA special products?
Catecholamines, dopamine, acetylcholine, GABA, serotonin, melotonin, NO
What AA is serotonin (5-HT) formed from?
tryptophan
Arginine is used to synthesize which neurotransmitter?
Nitrous Oxide
What are some specialized functions of NO?
used by macrophages in the nitrogenous burst, vascular endothelial vasodilatory factor, CNS second messenger
Glycine and arginine are used to synthesize_____.
Creatine (also creatinine)
What is the function of Glutathione? (aka GSH)
it acts as a non-toxic reservoir of reducing power ( instead of using strictly cysteine, which would be toxic)
What are the major polyamines, and what is their general function?
Putrescine, spermidine, and spermine… used for DNA synthesis ….derived from methionine and ornithine
What compounds are needed to form polyamines?
Ornithine and SAM
What AA is a precursor to melanin?
Tyrosine - def. in the enzyme for this conversion results in classical albinism
This vasodilator substance is the result of decarboxylation of histidine.
Histamine
Decarboxylation of serine can form these special products.
Choline and Ethanolamine
