amino acids Flashcards
After the first step of the nitrogen extraction, the carbon skeletons of the 20 amino
acids are metabolized into several metabolites
-pyruvate and intermediates in the TCA cycle (oxaloacetate, succinyl CoA,
fumarate, and α-ketoglutarate) –>can be used for gluconeogenesis (glucogenic)
-acetyl-CoA and acetoacetyl CoA –>can be used for fatty acid synthesis or
ketogenesis (ketogenic
Ile, Thr, Phe, Tyr, and Trp are both _____ and ______
glucogenic and ketogenic
Lys and Leu are purely _____
ketogenic
some of the nonessential amino acids are _____ because essential amino acids are necessary for their synthesis
conditionally essential
all other amino acids are
glucogenic
_______ amino acids cannot be synthesized by the body or synthesized but not enought
essential
nonessential amino acids
alanine, aspartate, asparagine, glutamate, serine
a-keto acids
-The removal of the amine group from amino acids produces α-keto acids.
-Some of the α-keto acids are readily available as intermediates in glycolysis or the TCA cycle.
alanine makes what a-keto acid
pyruvate
aspartate makes what a-keto acid
oxaloacetate
glutamate makes what a-keto acid
a-ketoglutarate
transamination
-The removal of the amine group from an amino acid is coupled with the production
of glutamate from α-ketoglutarate.
-Catalyzed by amino-acid-specific aminotransferases (or transaminases).
-Requires pyridoxal phosphate as a cofactor.
Glutamate + Oxaloacetate ⇌ α-Ketoglutarate + ?
A. Glutamine
B. Alanine
C. Serine
D. Aspartate
E. Pyruvate
D. aspartate
oxidative deamination- glutamate dehyrogenase
-Amine groups of amino acids are released as ammonia.
-Glutamate dehydrogenase removes the amine group from glutamate by
producing ammonia and NADH.
-Glutamate dehydrogenase can catalyze the reverse reaction using NADPH, but
under normal conditions [NH 4+] is too low for the reaction to occur.
Oxidative deamination – amino acid oxidase
-Amino acid oxidase removes the amine group of an amino acid as ammonia.
-Not significant contribution to metabolism
glutamine, an ammonia transporter
-Because ammonia is toxic, ammonia is transported in nontoxic form as amino
acids (glutamine and alanine).
-Glutamine is the most abundant circulating amino acid.
_____produces glutamine from glutamate and ammonia.
-glutamine synthetase
-reaction requires input of energy
most glutamine is transported to the _____ and converted to alanine and ammonia
-intestines
in the liver alanine is converted to
-pyruvate- glucose (gluconeogenesis)
-ammonia- urea (urea cycle)
Metabolites derived from amino acids
-Glutamate → γ-aminobutyrate (GABA)
-Tyrosine → dopamine, norepinephrine, epinephrine
-Tryptophan → serotonin, melatonin
-Histidine → histamine
-Glycine → oxalate
γ-Aminobutyrate (GABA)
-Produced from glutamate by glutamate decarboxylase
-Inhibitory neurotransmitter produced by GABAergic neurons
-Reduces neuronal excitability
-Causes a negative change in the membrane potential (hyperpolarization)
-Glutamate as is also functions as an excitatory neurotransmitter.
______ is a neurotransmitter; the end product in
the substantia nigra of the brain.
-dopamine
-Insufficient production of dopamine causes Parkinson
disease
In the adrenal medulla, dopamine is further converted
to _____ and ______, which are
catecholamines functioning as fight-or-flight hormones.
norepinephrine and epinephrine
tryptophan dervatives
serotonin and melatonin
________is a neurotransmitter in CNS, regulating mood, appetite, and sleep. and regulates gastrointestinal motility in the GI tract.
serotonin
_____ is involved in regulation of circadian rhythm; synthesized mostly at night
and induces sleep.
melatonin
histamine
-Produced by decarboxylation of histidine.
-Released from cells as an allergic response, causing vasodilation and itchiness
(histamine H 1 receptor).
-Acts as a neurotransmitter in CNS, promoting wakefulness (histamine H 1 receptor).
-Promotes gastric acid release (histamine H 2 receptor)
oxidation of glycine
-Excessive production of oxalate (hyperoxaluria) forms the insoluble calcium oxalate salt, which may lead to kidney stones.
-About 50% of oxalate comes from the diet (ex. peanut, spinach, chocolate).
-Lack of the enzyme activity converting glyoxylate to
glycine causes primary hyperoxaluria.
