MCP - Schmitt - Amino Acid Degradation and the Urea Cycle - 2/20

Question 1

How are proteins degraded and aa’s absorbed?

Answer 1

Amino acids are taken up into from the intestinal lumen via Na or H cotransporters. There are 5 main kinds.
Amino acids are degraded to urea and CO2, or made into pyruvate (alanine, serine)

Question 2

What is Hartnup’s disease?

Answer 2

Hartnup’s disease is a defect in the transport system for neutral and aromatic amino acids including tryptophan from the gut and renal tubules.
Symptoms are niacin deficiency (pellagra), diarrhea, dermatititis and dementia, all leading to death
Tx with niacin
Diagnose by high levels of neutral and aromatic amino acids in the urine and feces

Question 3

What is cystinuria?

Answer 3

A defect in the transport system for basic amino acids and cystine (2 cysteines) from the gut and the renal tubules
Symptoms are UTIs ad kidney stones bc cystines form crystals
Tx with fluids, pencillamine, which makes cystine more solube

Question 4

What are the abundant amino acids?

Answer 4

Glutamine and Alanine are the most abundant amino acids in serum.

• *Glutamine has 2 NH2 groups.
• *Glutamine is a major carrier of NH4+ groups in the blood.

Question 5

What are the essential amino acids?

Answer 5

Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine
Arginine (enough for growth)
PVT TIM HALL
•	Tyrosine can become and essential amino acid! (made from phenylalanine, so if phenylalanine is limiting than tyrosine becomes essential)
•	Same for cystine (made from thyionine, so if thyionine is limiting than tyrosine becomes essential)

Question 6

What is nitrogen balance? What is positive, negative balance? Who would you expect to have a positive Balance?

Answer 6

If the total daily nitrogen loss in urine, skin and feces is equal to the total daily nitrogen intake.
Positive balance - N losses are less than intake
(Children, Body builders, people recovering from injuries that don’t degrade as much AAs as they take in, in order to build muscle)
Negative balance - N losses are greater than intake

Question 7

What are amino acids used for?

Answer 7

To make proteins

To be broken down to carbon compounds for assembly into fat, or further breakdown to make energy

Question 8

What is the urea cycle?

Answer 8

The method of removing nitrogenous waste products through the urine while maintaining blood pH in a normal range.
Urea can carry 2 ammonia groups, is soluble, non-protonatable and inert.
The urea cycle happens mainly in the liver, but some in the kidneys.

Question 9

How do humans deal with and dispose of ammonia?

Answer 9

Pee it out

Question 10

What is pyridoxyl phosphate?

Answer 10

Pyridoxal phosphate is an essential vitamin, B6, and is a cofactor critical for NH4+ transfer reactions

Question 11

What is a transamination reaction?

Answer 11

Movement of NH group from one compound to another

Question 12

What are the metabolic diseases associated with the urea cycle?

Answer 12

Hyperornithinemia
Citrullinemia (only ones that causes mental retardation)
Hyperammoniemia
Argininosuccinic aciduria
Arginiemia
One disease for every enzyme in the pathway

Question 13

T/F: Humans can synthesize ammonia.

Answer 13

False

Question 14

E and Q are collecting sites for:

Answer 14

Ammonia groups

Question 15

___ becomes an essential amino acid if methionine is low.

Answer 15

Cysteine

Question 16

Tyrosine becomes an essential amino acid if ____ is low.

Answer 16

Phenylalanine

Question 17

How do CF patients deal with pancreatic upset, via defective pancreatic enzymes and/or hardening of the ancreatic duct?

Answer 17

They must take pancreatic enzyme supplements.

Question 18

Why do disorders associated with defects in amino acid transport lead to increased levels of amino acids in the urine?
Why is it possible to have 1 of the 5 defective amino acid transporters without major health consequences?

Answer 18

Same transporters in both the intestine and the kidney

High degree of redundancy in the transporters’ functions.

All of these transporters are Na or proton symporters

Question 19

The urinary levels of what aa provide a measure for protein breakdown?

Answer 19

Histidine

Question 20

What is kwashiorkor syndrome?

Answer 20

The absence of lysin in low-grade cereal proteins, used as a dietary mainstay in underdeveloped countries, leads to an inability to synthesize protein (bc of missing essential amino acids).

Question 21

T/F: Alanine can easily be made from pyruvate.

Answer 21

True

Alanine + alpha-ketoglutarate pyruvate + glutamate

Question 22

What is the most common genetic deficiency in the urea cycle?

Answer 22

Ornithine transcarbamoylase, enzyme for step 2
X-linked
Hyperornithinemia

Question 23

What aa becomes essential in most metabolic disorders of the urea cycle?

Answer 23

Arginine

Patients are treated with a low protein diet supplemented with arginine and sometimes citrulline