Amino Acids

Question 1

State three sources for the amino acid pool

Answer 1

1. Dietary protein
2. Tissue breakdown
3. Synthesis of non-essential amino acids

Question 2

Discuss Gluconeogenesis

a. Definition of each term
b. Starting and ending products for each pathway
c. Organ in which the pathways occur in the body

Answer 2

a. The formation of glucose from non-carbohydrate sources, such as amino acids, glycerol, or fatty acids

b. Starting: amino acids (from protein), glycerol (from fat), and fatty acids (from fat)
Ending: Glucose

c. Mainly the liver, to some extent in the kidneys

Question 3

Discuss Transamination

a. Definition of each term
b. Starting and ending products for each pathway
c. Organ in which the pathways occur in the body

Answer 3

a. The process of amino group transfer to make different amino acids
b. Starting and Ending: from one amino acid to another
c. Liver

Question 4

Discuss Deamination

a. Definition of each term
b. Starting and ending products for each pathway
c. Organ in which the pathways occur in the body

Answer 4

a. The removal of the amino group, forming toxic ammonia

b. Starting: Ammonia
Ending: Urea

c. Mainly the liver, to some extent in the kidneys

Question 5

Differentiate the mechanisms and both plasma and urine amino acid levels (increased, decreased, or normal) in overflow and renal aminoacidurias

Answer 5

Renal aminoaciduria:

Renal reabsorptive mechanism is defective within the kidney – increased urine levels of amino acid (AA), plasma levels are decreased to normal of AA

Overflow aminoaciduria:

Plasma level of AAs exceed the renal threshold (kidney function is normal) – plasma and urine levels of AA are increased

Question 6

What are the three (3) primary renal aminoacidurias?

Answer 6

1) Cystinuria
2) Hartnup disease
3) Fanconi syndrome

Question 7

Differentiate the three primary renal aminoacidurias (Cystinuria, Hartnup disease, and Fanconi syndrome) according to:

a. Specific renal defect
b. Clinical/laboratory features present in each condition

Answer 7

Cystinuria

a. Renal reabsorptive mechanism is defective for specific AAs including cystine, ornithine, lysine, and arginine
b. Cystine crystals present on urine microscopic examination

Hartnup disease

a. lntestine and renal reabsorptive mechanism(s) are defective for neutral monocarboxylic AAs
b. Increased AAs in the urine, specifically neutral monocarboxylic AAs; may also have a Vitamin B deficiency, may present with Pellagra

Fanconi syndrome

a. Proximal convoluted tubule is defective for AAs, glucose, bicarbonate, etc.
b. Polyuria, dehydration, acidosis, etc.

Question 8

What are the five (5) primary overflow aminoacidurias?

Answer 8

1. Phenylketonuria
2. Type I, II, III Tyrosinemias
3. Alkaptonuria
4. Homocystinuria
5. Maple Syrup Urine Disease (MSUD)

Question 9

Phenylketonuria (unable to convert phenylalanine to tyrosine)
[feen-nol-key-tone-uria]
a. Specific enzyme deficiency
b. Clinical/laboratory features present in each condition

Answer 9

a. Phenylalanine hydroxylase

b. Spastic movements and seizures, mental retardation, feeding difficulties, delayed mental/social development,
hypopigmentation
Increased serum phenylalanine
Decreased serum tyrosine

Question 10

Type I Tyrosinemia
[tyrone-seen-e-uhhh]

a. Specific enzyme deficiency
b. Clinical/laboratory features present in each condition

Answer 10

a. Fumarylacetoacetase

b. Cirrhosis
Increased serum and urine tyrosine levels
Elevated methionine

Question 11

Type II Tyrosinemia
[tyrone-seen-e-uhhh]

a. Specific enzyme deficiency
b. Clinical/laboratory features present in each condition

Answer 11

a. Tyrosine aminotransferase

b. Variety of eye issues (i.e. excessive tearing, sensitivity to light, pain and redness), skin lesions on palms and hands –
Increased serum and urine tyrosine levels, NOT elevated methionine in serum
Tyrosine crystals in urine

Question 12

Type III Tyrosinemia
[tyrone-seen-e-uhhh]

a. Specific enzyme deficiency
b. Clinical/laboratory features present in each condition

Answer 12

a. 4-hydroxyphenylpyruvate dioxygenase

b. Seizures, retardation, and periodic ataxia

Question 13

Alkaptonuria

a. Specific enzyme deficiency
b. Clinical/laboratory features present in each condition

Answer 13

a. Homogentisic acid oxidase

b. Urine turns brown/black when exposed to light and air or when alkali is added
Homogentisic acid increases in serum and urine

Question 14

Homocystinuria

a. Specific enzyme deficiency
b. Clinical/laboratory features present in each condition

Answer 14

a. Cystathionine beta synthase (CBS)

b. Ocular, skeletal abnormalities and cardiovascular issues
Elevated levels of methonine and homocystine in serum and urine

Question 15

Maple Syrup Urine Disease

a. Specific enzyme deficiency
b. Clinical/laboratory features present in each condition

Answer 15

a. Alpha-ketoacid decarboxylase

b. Hypoglycemia, ketoacidosis, etc.
Urine possesses a sweet smell due to the presence of the branched chain amino acids, detected by the 11th day of life

Question 16

State the specific physical characteristics of urine collected from an alkaptonuric or maple syrup urine disease patient.

Answer 16

Alkatonuria: urine turns brown/black when exposed to light and air or when alkali is added

Maple Syrup Urine Disease (MSUD): Urine possesses a sweet smell

Question 17

10. Recognize the general principles of the following screening/qualitative analytical techniques for amino acid measurements:
    a. Thin-layer chromatography
    b. Photometric screening tests
    c. Guthrie test

Answer 17

a. Previously performed in other classes – understand well enough
b. Similar to using a spectrophotometer – a reagent is added to the substance and absorbance/%T can be detected
c. If there is enough AAs present in the sample, the bacteria will “outcompete” the inhibitor and grow around it

Question 18

List three quantitative tests for the presence of aminoacidurias.

Answer 18

1. Ion-exchange chromatography
2. Gas-liquid chromatography
3. High performance liquid chromatography