Ammonia metabolism test Flashcards
What is A?
Glutamate
What is B?
NH3
What is C?
Transaminases
What is D?
deaminases
What advantages are given by the fact that fatty acid synthesis is not just a reversal of fatty acid beta oxidation?
greater flexibility (substrates and intermediates can be different). better control (can be controlled independently or co-ordinately).
What 6 things can a C5 skeleton produced from transamination provide?
pyruvate, oxaloacetate, fumarate, a-ketoglutarate, succinate, acetyl~CoA
Give three common features of amino acid catabolism, and the products
The C-atoms are converted to intermediates of carbohydrate metabolism (glucogenic amino acids) or lipid metabolism (ketogenic amino acids)
The N-atoms are usually converted to urea for excretion in the urine but some may be excreted directly as ammonia and some may be converted to glutamine and used for the synthesis of purines and pyrimidines.
The first step in the various pathways usually involved the removal of the –NH2 group by transamination or deamination.
Products = urea, pyruvate, acetyl~CoA, -ketoglutarate, oxaloacetate, succinate and fumarate.
Describe the processes which produce ammonia in the body (3)
L&D-amino acid oxidases are low specificity enzymes that convert amino acids to keto acids and NH3.
Glutaminase is a high specificity enzyme that converts glutamine to glutamate + NH3.
Glutamate dehydrogenase is a high specificity enzyme that catalyses the reaction:
Glutamate + NAD+ + H2O –> a-ketoglutarate + NH4+ + NADH + H+
How is ammonia removed from the body?
Ammonia is removed from the body by:
Conversion to urea in the liver. The urea is removed from the body in the urine via the kidney.
Conversion to glutamine using glutamate and used for purine and pyrimidines synthesis.
Excretion as ammonium ion in urine.
Give three ways in which homocysteinuria can be treated
B6 supplements increase CBS enzymes in 50% of cases
Decrease quantity of homecysteine in the diet
Increase levels of B12, which conversts homocysteine to less harmful methionine
How does phenyl alanine cause mental retardation?
Phenyalanine saturates transporters of aminoacids BBB, so other essential amino acids cannot enter brain. LNAAT transporter works via active transport, so ir rate limiting. This lack of other amino acids slows synthesis of neurotransmitters and proteins in brain cells, causing mental retardation.
