13 Flashcards
The 20 catabolic pathways converge to form six major
products (all of which enter the citric acid cycle
pyruvate acetyl coa
Succinyl cos
Aketogluterate fumarate oxaloacetate
Ketogenic amino acids
can yield ketone bodies in the
liver
phenylalanine, tyrosine, isoleucine, leucine,
tryptophan, threonine, and lysine
Glucogenic amino acids
can be converted to glucose and
glycogen
all amino acids except lysine and leucine
One-carbon transfers usually involve one of three cofactors
Biotin (transfers CO2)
– Tetrahydrofolate (transfers intermediate oxidation states)
– S -adenosylmethionine (transfers methyl groups)
– Tetrahydrobiopterin = participates in oxidation reactions
Seven amino acids are degraded to Acetyl-CoA
Leucine, lysine,phenylalanine, tyrosine,and tryptophan yield acetyl-CoA via acetoacetyl-CoA
Isoleucine, leucine, threonine, and tryptophan form acetyl-CoA directly
Containing aromatic ring
Phenylalanine (Benzene ring or phenol)
– Tyrosine (Phenol), and
– Tryptophan (indole
Phenylalanine and tyrosine are degraded into
acetoacetyl-CoA (and thus acetyl-CoA) and fumarate
Phenylalanine —> tyrosine
Disease, enzyme, cofactor
Phenylketonuria (PKU)
Phenylalanine hydroxylase
Tetrahydrobiopterin (carries electrons from NAD(P)H to O2) and becomes oxidized to dihydrobiopterin
Alkaptonuria
disease caused by a genetic defect in homogentisate dioxygenase
Five Amino Acids Are Converted to α-Ketoglutarate
Arginine, glutamate,
glutamine, histidine, and
proline
Glutamate is deaminated to
α-ketoglutarate
Four Amino Acids Are Converted to Succinyl-CoA
Isoleucine,
methionine,
threonine, and
valine
the aminotransferase is absent in
liver
degraded only in extrahepatic tissues (muscle, adipose, kidney, brain)
branched-chain amino acids
(isoleucine, leucine, and valine
Maple syrup urine disease
Phosphorylation of Branched-chain α-keto acid dehydrogenase complex
condition in which the three branched-chain α- keto acids and their precursor amino acids accumulate in the blood and “spill over” into the urine
Isoleucine yields
valine yields
acetyl CoA and propionyl CoA
CO2 and propionyl CoA
Asparagine and aspartate are
degraded to
oxaloacetate
Asparagine ==> oxaloacetate
Asparagine, Asparaginase, aspartate, Aspartate aminotransferase (catalyzes the transamination of aspartate with α-ketoglutarate) ,glutamate and oxaloacetate
Six Amino Acids Are Degraded to Pyruvate
Alanine, tryptophan,
cysteine, serine, glycine,
and threonine
Serine dehydratase
the conversion of
serine to pyruvate
Degradation of Glycine
1-hydroxylation to serine then pyruvate
2-glycine cleavage enzyme
3- D-amino oxidase
Catabolism of Cysteine
Transamination pathway (glutathione )
– Direct oxidative pathway (taurine)
Amino acid and nucleotide biosynthetic pathways make
use of biological cofactors
pyridoxal phosphate
tetrahydrofolate
S -adenosylmethionine
Nitrogen enters by way of
glutamate and glutamine
Carbon skeleton derive from
intermediates of:
CAC:
a-ketoglutarate, oxaloacetate
• Glycolysis
– pyruvate, 3-phosphoglycerate,phosphoenolpyruvate
• Pentose phosphate pathway
– ribose 5-phosphate, erythrose 4-phosphate
Isoleucine from
Oxaloacetate and pyruvate
Ribose 5-phosphate
Histidine
Phosphoenolpyruvate and
erythrose 4-phosphate
Tryptophan
Phenylalanine
Tyrosine
Essential AA
Pyruvate.
Phosphoenolpyruvate and erythrose 4-phosphate
Ribose 5-phosphate
Oxaloacetate 2
Glutamine is made from Glu
by glutamine synthetase
1. Phosphorylation of Glu
Gama glutamyl phosphate
