Amino Acid Metabolism EC

Question 1

Nitrogen containing substances are used in the synthesis of what compounds?

Answer 1

Nucleotides
Neurotransmitters
Hormones
Porphyrins
Nonessential amino acids

Question 2

What are the essential amino acids?

Answer 2

Phenylalanine
Valine
Tryptophan
Threonine
Isoleucine
Methionine
Histidine
Leucine
Lysine

Question 3

Which amino acids are acidic?

Answer 3

Aspartate

Glutamate

Question 4

Tremor, slurred speech, somnolence, vomiting, cerebral edema, and blurred vision

Answer 4

Ammonia intoxication
Liver disease or urea cycle enzyme deficiency
NH4 accumulates and depletes a-ketoglutarate (blocks TCA)

Question 5

What happens to carbon skeletons of amino acids after the ammonia has been removed?

Answer 5

They are degraded and become intermediates in the TCA cycle

Some are ketogenic: Lysine & Leucine
Some are both: Isoleucine, Phenylalanine, Typrtophan, & Tyrosine
Some are glucogenic: rest

Question 6

Tyrosine derivatives

Answer 6

Thyroid hormones

DOPA (dopamine, NE/Epi, melanin)

Question 7

Methionine

Answer 7

S-Adenosylmethionine (SAM) - methyl group transfers
Homocysteine
Cysteine

Question 8

Tryptophan

Answer 8

Niacin
Serotonin
Melatonin

Question 9

Glutamate

Answer 9

GABA

Glutathione

Question 10

Glycine

Answer 10

Porphyrin (heme)

Question 11

Arginine

Answer 11

Creatine
NO
Urea

Question 12

Histidine

Answer 12

Histamine

Question 13

Phenylalanine

Answer 13

Tyrosine (dopa, thyroid hormones)

Question 14

What does phenylalanine hydroxylase do?

Answer 14

Convert Phenylalanine to Tyrosine

Question 15

Man presents with knee and back pain. Dark spots on conjunctiva and nasal bridge. Urine turns dark if forgets to flush.

Answer 15

Alkaptonuria
Defective homogentisic acid oxidase (degrades tyrosine)
Tyrosine, Phenylalanine, and Homogentisic acid build up

Question 16

Presents to ER with sudden severe, intermittent right flank pain w/ n/v. Urinalysis shows hematuria. Kidney stones with cysteine crystals found.

Answer 16

Cystinuria
Defective transport of Cysteine, Ornithine, Arginine, & Lysine “COAL”

Cystosis - intralysosomal accumulation of cysteine

Question 17

Fanconi Syndrome

Answer 17

Renal proximal tubule dysfunction (hypophosphatemia, glycosuria, amino aciduria, hypokalemia)

Growth retardation, rickets, polyuria, dehydration, metabolic acidosis, photophobia.

Question 18

Man complaining of photosensitive rash on face and neck and extensor surfaces. Has been feeling more irritable than normal and is somewhat ataxic. Eats healthy with a well balanced diet.

Answer 18

Hartnup disease
Mutation in neutral a.a. transporter
Tryptophan excreted in urine and not absorbed in gut
Leads to niacin deficiency-pellagra

Question 19

7 yo boy presents complaining of diminished visual acuity. On p/e, lenticular dislocation found along with abnormally long fingers. Has mild mental retardation. Labs reveal elevated serum methionine and urine homocysteine.

Answer 19

Homocystinuria

Defects: 
Cystathionine synthase (or PP/B6 cofactor affinity). Homocysteine methyltransferase

Homocysteine accumulates-
toxic to vascular endothelium (atherosclerosis),
interferes with collagen formation (ocular/skeletal)

Question 20

4 day old infant presents because vomiting and urine smells sweet. Moro reflex absent and rigid. Labs show metabolic acidosis.

Answer 20

Maple Syrup Urine Disease
Defect in BCKD (branched chain ketoacid dehydrogenase)
Diminished breakdown of Isoleucine, Leucine, & Valine
“I Love Vermont Maple Syrup”

Ketoacids toxic to brain
Branched chain a.a.’s in urine lead to sweet smell

Question 21

2 y/o blonde haired blue eyes immigrant presents with possible developmental delays. Hypertonia and hyperreflexia and smells “musky”. Guthrie test positive, phenylketones in urine.

Answer 21

PKU (phenylketonuria)
Defect in Phenylalanine Hydroxylase or tetrahydrobiopterin cofactor (converts phenylalanine to tyrosine)
Phenylalanine buildup causes brain damage (and becomes deficient in tyrosine derivatives)
Avoid foods w/ phenylalanine (aspartame)