Amino Acid Degradation and the Urea Cycle - ME

Question 1

What are the most abundant amino acids in serum?

Answer 1

Glutamine and alanine

Question 2

If methionine is low what amino acids becomes essential?

Answer 2

Cysteine

Question 3

If phenylalanine is low what amino acids becomes essential?

Answer 3

Tyrosine

Question 4

Patients with cystic fibrosis must be supplement with?

Answer 4

pancreatic enzymes

Question 5

How many transporters have been identified for the transport of amino acids from the gut into intestinal epithelial cells?

Answer 5

5, all of which are Na or proton symporters

Question 6

What is hartnups disease?

Answer 6

A defect in the transport system for neutral and aromatic amino acids from the gut and the renal tubules.

Question 7

What are the symptoms of hartnups Disease?

Answer 7

Similar to pellagra (niacin deficiency, 4D’s: Diarrhea, Dermatitis, Dementia, Death)

Question 8

How do you treat hartnups disease?

Answer 8

Administration of niacin

Question 9

What is cystinuria?

Answer 9

A defect in the transport system for basic amino acids and cystine (a disulfide- linked dimer of cysteine) from the gut and the renal tubules.

Question 10

What are some symptoms of cystinuria?

Answer 10

Cystine is relatively insoluble and forms crystals which can lead to urinary tract infections and kidney stones.

Question 11

What amino acid is use to test muscle breakdown?

Answer 11

Histidine residues of the muscle protein actomyosin are methylated posttranslationally. When actomyosin is broken down, 3-methyl histidine is liberated and excreted into the urine.

Question 12

Define Positive balance

Answer 12

If nitrogen losses are less than intake, the subject is in positive nitrogen balance, as in children and convalescing adults.

Question 13

Define Negative balance

Answer 13

If nitrogen losses are more than intake, the subject is in negative nitrogen balance, as in diseases involving wasting or starvation.

Question 14

What is kwashiorkor syndrome?

Answer 14

The absence of lysine in low-grade cereal proteins, used as a dietary mainstay in many underdeveloped countries, leads to an inability to synthesize protein

Question 15

Free ammonia ion is highly poisonous so the body can move remove free NH + in three ways. What are the three ways?

Answer 15

1. Glutamate Dehydrogenase
2. Glutamine Synthase, reversible by Glutaminase
3. Carbamoyl Phosphate Synthase I and II

Question 16

What is transamination and what cofactor does it utilize?

Answer 16

The transfer of an amino group from an amino acid to an α-keto acid to form a new amino acid and a new keto acid.
Cofactor - Pyridoxal phosphate (vitamin b6): an essential cofactor for all transaminations.

Question 17

Name all 5 reactions Pyridoxine functions as a cofactor.

Answer 17

1) transaminations
2) decarboxylations
3) dehydration of ß-hydroxyamino acids
4) racemizations of α-amino acids
5) removal of H2S from cysteine

Question 18

Most transaminases converge what amino acid?

Answer 18

glutamate

Question 19

Describe how the liver uses glutatmate.

Answer 19

Glutamate is deaminated mainly in the liver. If the liver needs energy it will generate NADH for electron transport. If it is energy rich, it will generate NADPH for biosynthetic reaction.

Question 20

What are some alternate mechanisms for amino acid deamination

Answer 20

1. Amino acid oxidases- Both L and D-amino acid oxidases occur in the kidneys and the liver.
2. Direct deamination by dehydratases
3. Desulfhydrases- Homocysteine desulfhydrase is also a pyridoxal phosphate containing enzyme that removes both ammonia and sulfur from homocysteine.

Question 21

Name the two urea cycle enzymes compartmentalized in the mitochondrial

Answer 21

A. Mitchondria
carbamoylphosphate synthetase
ornithine transcarbamoylase

Question 22

Name the two urea cycle enzymes compartmentalized in the cytosol

Answer 22

B. Cytosol

argininosuccinate synthetase argininosuccinate lyase arginase

Question 23

List the 6 reactions in the urea cycle

Answer 23

1. Carbamoylphosphate is formed from ammonia and CO2.
2. Citrulline is formed from carbamoylphosphate and ornithine in a reaction that is catalyzed by ornithine transcarbamoylase (OTC).
3. Argininosuccinate is formed from citrulline and aspartate.
   4) Aspartate is generated arises from the transamination of oxaloacetate by glutamate.
4. Arginine and Fumarate are formed from the cleavage of argininosuccinate
5. Urea and Ornithine are formed from the cleavage of arginine.