Amino Acid Metabolism

Question 1

Source of METHYL groups in metabolism

PRECURSOR of CYSTEINE

Answer 1

METHIONINE

Question 2

Synthesized from methionine and ATP

Answer 2

S- ADENOSYLMETHIONINE (SAM)

Question 3

Enzymes involved in metabolism of sulfur containing amino acid

Answer 3

Methiobine adenosyl transferase
Methyl transferase
Adenosyyl homocysteinase
Methionine synthase
Cystathionine B synthase
Cystathionase

Question 4

After donating its methyl group SAM is converted to

Answer 4

S-ADENOSYLHOMOCYSTEINE

Question 5

Catecholamines are inactivated (catabolized) by

Answer 5

MONOAMINE OXIDASE (MAO) and CATECHOL O METHYLTRANSFERASE (COMT)

Question 6

NE and Epi are degraded to

Answer 6

VANILLYMANDELIC ACID (VMA)

increased in pheochromocytoma

Question 7

Dopamine is degraded to

Answer 7

HOMOVANILLIC ACID (HVA)

Question 8

DOPA Decarboxylase

Answer 8

L-DOPA – DOPAMINE

COFACTOR - B6 (pyridoxine)

Question 9

Dopamine beta hydroxylase

Answer 9

DOPAMINE – NOREPINEPHRINE

COFACTOR: VITAMIN C

Question 10

The MC metabolic disorder concerned w/ amino acid

Answer 10

Classic Phenylketonuria

Question 11

Biochemical defect in PKU

Answer 11

PHENYLALANINE HYDROXYLASE DEFICIENCY

Question 12

Phenylalanine hydroxylase

Answer 12

L PHENYLALANINE –> L TYROSINE

Question 13

Phenylalanine hydroxylase

Answer 13

L PHENYLALANINE –> L TYROSINE

Question 14

Phenylketonuria

ACCUMULATION OF PHENYLKETONES
phenylpyruvate (characteristic odor to the urine)
phenyllactate
phenylacetate

Answer 14

mental retardation
musty odor
vomiting
hyperactive with autistic behavior
lighter in their complexion than unaffected siblings

Question 15

The main organ affected by hyperphenylalaninemia

Answer 15

BRAIN

Question 16

Treatment of Classical PKU

Answer 16

Dietary control to DECREASE PHENYLALANINE AND INCREASE TYROSINE

AVOID:
HIGH protein foods - meat, dairy, nuts, legumes

starches - bread, potatoes, corn and beans

ALLOWED
LOW protein foods - fruits, nonstarchy vegetables

Question 17

Congenital deficiency of HEMOGENTISATE OXIDASE in the degradative pathway of tyrosine –> build up of HOMOGENTISIC ACID

Answer 17

ALKAPTONURIA

Question 18

Alkaptonuria

Answer 18

alkapton bodies –> urine turn black on standing

dark CT (OCHRONOSIS)

benign disease but may have DEBILITATING ARTHRALGIAS

pigment deposition

Question 19

GARRODS TETRAD

Answer 19

Alkaptonuria
Albinism
Pentosuria
Cystinuria

Question 20

Treatment for alkaptonuria

Answer 20

aimed at reducing pigment deposition

reduce phenylalanine and tyrosine

VITAMIN C

Question 21

Defective melanin synthesis from TYROSINE

Answer 21

ALBINISM

absence of copper requiring enzyme TYROSINASE

defective tyrosine transporters

Question 22

Specialized products from TYROSINE

Answer 22

MELANIN
CATECHOLAMINES
THYROXINE

Question 23

Type I Tyrosinemias

Answer 23

FUMARYL ACETOACETATE HYDROLASE DEFICIENCY

cabbage like odor

Question 24

Type II Tyrosinemia

Answer 24

TYROSINE TRANSAMINASE DEFICIENCY

Question 25

MC inborn error of methionine metabolism

Answer 25

Classic Homocystinuria

Question 26

Enzyme deficient in Homocystinuria

Answer 26

CYSTATHIONINE B SYNTHASE COENZYME: Pyridoxal phosphate

Question 27

Defect in methionine degradation leads to

Answer 27

HIGH PLASMA AND URINARY LEVELS OF HOMOCYSTEINE AND METHIONINE LOW LEVELS OF CYSTEINE

Question 28

Homocystinuria

Answer 28

normal at birth 3 y/o - subluxation of the ocular lens (ECTOPIA LENTIS) -- severe myopua and iridodonesis (quivering of the iris) displacement is DOWNWARD progressive INTELLECTUAL DISABILITY SKELETAL ABNORMALITIES - tall, thin, w/ elongated limbs, arachnodactyl, pectus excavatum or carinatum, genu valgum, pes cavus THROMBOEMBOLIC EPISODES - both large and small vessels * MI * stroke in the young

Question 29

Diagnostics of Homocystinuria

Answer 29

ELEVATIONS - methionine and homocystine (or homocysteine) LOW - cystine in the plasma

Question 30

Treatment of Homocystinuria

Answer 30

Restriction of Methionine * limit eggs, fish and meat * encourage protein from plant foods (soya, nuts) Supplementation with vitamins B6, B12 and folate

Question 31

``` Inherited defect of renal tubular amino acid transporter for (COLA) CYSTINE ORNITHINE LYSINE ARGININE ```

Answer 31

CYSTINURIA excess cystine in urine --> precipitation if cystine kidney stones and staghorn calculi

Question 32

Treatment for Cystinuria

Answer 32

ACETAZOLAMIDE - alkalinize the urine

Question 33

Defect in the conversion of methylmalonyl CoA to succinyl CoA Involves metabolism of AA that ate converted to propionyl CoA: ISOLEUCINE, VALINE, THREONINE and METHIONINE

Answer 33

METHYLMALONIC ACIDEMIA seizure, encephalopathy, stroke at the age of 1 month to 1 year

Question 34

Treatment for Methylmalonic Acidemia

Answer 34

Protein Restricted diet (0.5 - 1.5 g/kg/d with L carnitine and cobalamin supplementation

Question 35

Blocked degradation of branched amino acids (ISOLEUCINE, VALINE, LEUCINE!!) d.t. deficiency in alpha ketoacid dehydrogenase complex

Answer 35

MAPLE SYRUP URINE DISEASE vomiting, seizures, mental retardation

Question 36

Treatment for Maple Syrup Urine Disease

Answer 36

Dietary restriction | Limit intake of valine, isoleucine and leucine

Question 37

Affected infants who are normal at birth develop poor feeding and vomiting in the 1st week of life lethargy, coma, convulsions metabolic acidosis hypertonicity, muscular rigidity with severe opisthonos

Answer 37

Maple Syrup Urine Disease

Question 38

Function of Histamine and Receptor Responsible for its Action

Answer 38

H1 - smooth muscle contraction; increased vascular permeability H2 - gastric HCL secretion H3 - synthesis and release of histamine in the brain

Question 39

Metabolic error d.t. deficiency of HISTIDASE histidase - converts HISTIDINE to UROCONATE

Answer 39

HISTIDINEMIA autosomal recessive benign