Amino Acid Metabolism

Question 1

What is the amino acid pool

Answer 1

It is the free amino acid available, found in very low concentration
It is found in equilibrium with between inside the cells and in the blood stream

Question 2

What can the amino acid pool be used for

Answer 2

Body proteins 
Urea, ammonia ( waste) 
Source of blood glucose in fasting 
NT's, haem 
creatine, purine, pyrimidines-----> uric acid and creatinine

Question 3

Why are protein requirements essential?

Answer 3

Protein is not stored in the body therefore it is needed in the diet to replace the lost amino acids which allows for tissue repair

Recommended- 50-70 g protein/day

Question 4

What are essential amino acids

Answer 4

They cannot be made in the body

Humans can only synthesise 10 amino acids
The other 10 Amino acids are found in the diet

Question 5

Comment on nitrogen balance

Answer 5

N intake = N excretion

ie the total amount of nitrogen take in as protein is equal to the total amount of nitrogen removed in urine as urea, uric acid, creatinine and ammonium

In addition to this the rate of body protein synthesis as well as other nitrogen containing molecules is equal to the rate of degradation

Question 6

N intake > N excretion

Answer 6

Protein synthesis exceeds the rate of breakdown

eg.
During normal growth in children
In convalescence after series illness
in pregnancy

This usually is not the case as high protein diet means that there’s surplus amino acids to be catabolised. excess nitrogen can be excreted as urea in urine

Question 7

N intake > N excretion

Answer 7

eg. in starvation
during serious illness
in late stages of some cancers

If not correct and is prolonged there is irreversible loss of essential body tissue

Question 8

Summarise the amino acid degradation

Answer 8

1. Transamination
   WITH AMINOTRANSFERASE
   Alpha amino-acid + 2-oxoglutarate —–> oxo acid + 2-glutamate
2. Release of NH2 group as ammonia

WITH GLUTAMATE DEHYDROGENASE
2-glutamate + NAD+ + H20 —–> 2-oxo-glutamate + NADH +H+ + NH4 +

3. i) can be metabolised by the TCA pathway to CO2 and H20 to provide a source of ATP
   ii) In starvation:

Glucogenic amino acids–> turned to pyruvate or citric acid components—-> CO2 + H20 OR Glucose

Ketogenic ( Leucine, lysine) —> turned to acetyl CoA —> CO2 + H20 OR Fat

Question 9

How is the liver involved in N metabolism

Answer 9

Removal of amino acids and glucose and fats from portal blood supply

Absorbed amino acids used for the synthesis of cellular proteins

Synthesis of plasm proteins

Synthesis of purines, pyramidines for DNA/RNA

Degradation of excess amino acids by trans deamination

Conversion of NH3 to urea

Question 10

Converting Glutamine to glutamates

Answer 10

glutaminase

H20—> NH3

Question 11

Converting glutmate to glutamine

Answer 11

glutamine synthase

ATP + NH3 —> ADP + Pi

Question 12

Why is glutamine useful

Answer 12

It can carry 2 ammonia equivalents to liver for urea formation
Safe carrier of ammonia- as ammonia is usually toxic
(neurotic- can cause coma, death and cerebal oedema0

Question 13

Urea cycle!!

Answer 13

NH4 + + CO2 + 2 ATP —-> carbonyl phosphate + 2ADP + pi

Question 14

Impaired conversion of NH3 to urea

Answer 14

Liver failure

genetic defects - reduction in catalytic activity of any enzyme of the urea cycle