amino acids

Question 1

After the first step of the nitrogen extraction, the carbon skeletons of the 20 amino
acids are metabolized into several metabolites

Answer 1

-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

Question 2

Ile, Thr, Phe, Tyr, and Trp are both _____ and ______

Answer 2

glucogenic and ketogenic

Question 3

Lys and Leu are purely _____

Answer 3

ketogenic

Question 4

some of the nonessential amino acids are _____ because essential amino acids are necessary for their synthesis

Answer 4

conditionally essential

Question 4

all other amino acids are

Answer 4

glucogenic

Question 5

_______ amino acids cannot be synthesized by the body or synthesized but not enought

Answer 5

essential

Question 6

nonessential amino acids

Answer 6

alanine, aspartate, asparagine, glutamate, serine

Question 7

a-keto acids

Answer 7

-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.

Question 8

alanine makes what a-keto acid

Answer 8

pyruvate

Question 9

aspartate makes what a-keto acid

Answer 9

oxaloacetate

Question 10

glutamate makes what a-keto acid

Answer 10

a-ketoglutarate

Question 11

transamination

Answer 11

-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.

Question 12

Glutamate + Oxaloacetate ⇌ α-Ketoglutarate + ?
A. Glutamine
B. Alanine
C. Serine
D. Aspartate
E. Pyruvate

Answer 12

D. aspartate

Question 13

oxidative deamination- glutamate dehyrogenase

Answer 13

-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.

Question 14

Oxidative deamination – amino acid oxidase

Answer 14

-Amino acid oxidase removes the amine group of an amino acid as ammonia.
-Not significant contribution to metabolism

Question 15

glutamine, an ammonia transporter

Answer 15

-Because ammonia is toxic, ammonia is transported in nontoxic form as amino
acids (glutamine and alanine).
-Glutamine is the most abundant circulating amino acid.

Question 16

_____produces glutamine from glutamate and ammonia.

Answer 16

-glutamine synthetase
-reaction requires input of energy

Question 17

most glutamine is transported to the _____ and converted to alanine and ammonia

Answer 17

-intestines

Question 17

in the liver alanine is converted to

Answer 17

-pyruvate- glucose (gluconeogenesis)
-ammonia- urea (urea cycle)

Question 18

Metabolites derived from amino acids

Answer 18

-Glutamate → γ-aminobutyrate (GABA)
-Tyrosine → dopamine, norepinephrine, epinephrine
-Tryptophan → serotonin, melatonin
-Histidine → histamine
-Glycine → oxalate

Question 19

γ-Aminobutyrate (GABA)

Answer 19

-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.

Question 20

______ is a neurotransmitter; the end product in
the substantia nigra of the brain.

Answer 20

-dopamine
-Insufficient production of dopamine causes Parkinson
disease

Question 21

In the adrenal medulla, dopamine is further converted
to _____ and ______, which are
catecholamines functioning as fight-or-flight hormones.

Answer 21

norepinephrine and epinephrine

Question 22

tryptophan dervatives

Answer 22

serotonin and melatonin

Question 23

________is a neurotransmitter in CNS, regulating mood, appetite, and sleep. and regulates gastrointestinal motility in the GI tract.

Answer 23

serotonin

Question 24

_____ is involved in regulation of circadian rhythm; synthesized mostly at night
and induces sleep.

Answer 24

melatonin

Question 25

histamine

Answer 25

-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)

Question 25

oxidation of glycine

Answer 25

-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.