Amino Acids

Question 1

Essential amino acids

Answer 1

PVT TIM HaLL: Phenylalanine, Valine, Tryptophan, Threonine, Isoleucine, Methionine,
Histidine, Leucine, Lysine.

Question 2

Phenylalanine derivatives

Answer 2

Phe–> Tyrosine–> Dopa –> Dopamine –> NE –> Epi

Phe–> Tyrosine–> Dopa –> Melanin

Question 3

Tyrosine derivatives

Answer 3

Tyrosine –> Thyroxine

Tyrosine –> Dopa –> Dopamine –> NE –> Epi

Question 4

Tryptophan derivatives

Answer 4

Tyrp –> Niacin–> NAD+ / NADP+

Tyrp –> Seretonin–> Melatonin

Question 5

Histidine derivatives

Answer 5

Histamine

Question 6

Glycine derivatives

Answer 6

Glycine –> Porphyrin –> Heme

Question 7

Glutamate Derivatives

Answer 7

Glutamate –> GABA

Glutamate –> Glutathione

Question 8

Arginine Derivatives

Answer 8

Arginine –> Creatine
Arginine –> Urea
Arginine –> Nitric Oxide

Question 9

PKU presentation

Answer 9

intellectual disability, microcephaly, seizures, hypopigmented skin, eczema, musty body odor.

Question 10

PKU treatment

Answer 10

decreased phenylalanine and increased tyrosine in
diet, tetrahydrobiopterin (BH4) supplementation

avoid the artificial sweetener aspartame

Question 11

Maternal PKU presentation

Answer 11

due to elevated maternal phenylalanine levels

microcephaly, intellectual disability, growth restriction, congenital heart defects.

Question 12

PKU enzyme

Answer 12

phenylalanine hydroxylase (AR)
Dihydropteridine reductase (reduced BH4) (malignant PKU)

Question 13

Difference between malignant and classic PKU

Answer 13

Malignant is a reduction in BH4 which is needed for syn of tyrosine, dopa, serotonin, and NO.

^ prolactin, decreased serotonin and NO.

Question 14

Maple Syrup Urine Disease presentation

Answer 14

vomiting, poor feeding, urine smells like maple syrup/burnt sugar. Causes progressive neurological decline

Question 15

Maple syrup urine disease defect

Answer 15

branched-chain α-ketoacid dehydrogenase (B1) (AR)

Blocked degradation of branched amino acids (Isoleucine, leucine, valine)

Question 16

Alkaptonuria presentation

Answer 16

bluish-black connective tissue, ear cartilage, and sclerae (ochronosis); 
urine turns black on prolonged exposure to air.
debilitating arthralgias (homogentisic acid toxic to cartilage).

Question 17

alkaptonuria enzyme

Answer 17

homogentisate oxidase (AR)

Question 18

Homocystinuria presentation

Answer 18

H- Homocysteine in urine,
O- Osteoporosis,
M- Marfanoid habitus,
O- Ocular changes (downward and inward lens subluxation),
C- Cardiovascular effects (thrombosis and atherosclerosis Ž stroke and MI),
S- kYphosis,

intellectual disability,
hypopigmented skin

Question 19

Homocystinuria defect

Answer 19

Possible causes:

• Cystathionine synthase deficiency
• ƒƒMethionine synthase (homocysteine methyltransferase)
• ƒƒMethylenetetrahydrofolate reductase (MTHFR) deficiency

(AR)

Question 20

Cystinuria presentation

Answer 20

recurrent

precipitation of hexagonal cystine stones

Question 21

Cystinuria defect

Answer 21

renal PCT and intestinal amino acid transporter that prevents reabsorption of Cystine, Ornithine, Lysine, and Arginine (COLA)

Question 22

Propionic acidemia or Methylmalonic acidemia presentation

Answer 22

poor feeding, 
vomiting, 
hypotonia, 
hepatomegaly, 
seizures 
high anion gap metabolic acidosis, 
ketoacidosis Ž 
hyperammonemia

Question 23

Propionic acidemia defect

Answer 23

propionyl-CoA carboxylase

Question 24

Methylmalonic acidemia defect

Answer 24

methylmalonyl-CoA mutase or

vitamin B12

Question 25

Ornithine transcarbamylase deficiency

Answer 25

Most common urea cycle disorder. X-linked recessive (vs other urea cycle enzyme deficiencies,
which are autosomal recessive).

Question 26

Ornithine transcarbamylase deficiency presentation

Answer 26

increased orotic acid in blood and urine, 
increased BUN,
symptoms of hyperammonemia.
No megaloblastic anemia (vs orotic aciduria).

Question 27

Urea Cycle

Answer 27

1. Citrulline 
\+Aspartate, (Argininosuccinate synthetase) 
2. Arginosuccinate
(arginosuccinate Lyase) = Fumarate
3. Arginine 
(Arginase) = Urea
4. Ornithine 
\+Carbamoyl phosphate, (ornithine transcarbamylase)

Question 28

Alaptonuria pathway

Answer 28

homogentisic acid–> maleylacetoacetic acid–> fumarate

Question 29

Homocystinuria Pathway

Answer 29

Homocystine–> cystathionine–> cysteine

Homocystine–> mathionine