Amino Acid Metabolism Flashcards
Name the 10 essential amino acids.
PVT TIM HALL
Phenylalanine
Valine
Threonine
Tryptophan
Isoleucine
Methionine
Histidine
Ariginine
Leucine
Lycine
What is the importance of dietary protein?
Required for synthesis of neurotransmitters, creatine, carnitine, haem, purines and pyrimidines.
What causes gout?
High uric acid released from metabolism of creatine, purines and pyrimidines
What is the average protein turnover in adults?
300-400g
What is the amino acid pool?
Free amino acids - there is no storage form of protein so high protein diet in excess is wasteful.
What is positive nitrogen balance? When does it occur?
Nitrogen intake is greater than nitrogen excretion.
During normal growth in children.
In convalescence after illness
In pregnancy
What is negative nitrogen balance? When does it occur?
When nitrogen intake is lower than nitrogen excreted.
Occurs during starvation.
During serious injury or trauma
If not corrected will lead to irreversible loss of body tissue - ultimately leading to death.
What is an amino acid?
Single unit of protein made up of amino group, carboxyl group and H-C-R variable group.
Amino acid = keto acid + amino group
How does pyruvate relate to alanine?
Pyruvate (keto acid) = HOOC-C=O-CH3
Alanine (amino acid) = HOOC-C(NH2)H-CH3
In alanine =O is replaced with NH2.
What is transamination?
Transfer of an amino group from one molecule to another.
Amino acid1 + keto acid2 > keto acid1 + amino acid2
Catalysed by aminotransferase enzyme
What enzymes catalysed transamination reaction?
Aminotransferase enzymes.
All contain prosthetic group derived from vitamin B6 - pyridoxal phosphate or pyridoxamine.
How is are amino acids used in gluconeogensis?
Carbon-skeleton of the amino acid will form part of the TCA cycle.
What is deamination?
Removal of an amino group from an amino acid to form a keto acid and ammonia.
Requires a co-enzyme.
amino acid + H2O + coenzyme > keto-acid + ammonia + reduced-coenzyme
What enzyme catalyses the deamination of L-glutamate to 2-oxo-glutarate?
Glutamate dehydrogenase
What are glucogenic amino acids?
13 amino acids
Their carbon-skeleton can be converted back to glucose by the liver
What are ketogenic amino acids?
Amino acids which can be degraded directly into acetyl CoA
Leucine and lysine are only degraded to acetyl CoA
Phenylalanine and tyrosine are both glucogenic and ketogenic.
Give 5 roles of the liver in nitrogen metabolism.
Removal of amino acids from portal blood supply
Absorption of amino acids for synthesis of cellular proteins and plasma proteins
Synthesis of haem, purines and pyrimidines for DNA and RNA
Degradation of amino acids by transdeamination
Conversion of NH3 to urea for excretion
How are amino groups transported to the liver?
Via glutamine in the blood.
Glutamine > Glutamate + NH3
What enzyme converts glutamine to glutamate?
Glutaminase
Uses H2O
What enzyme converts glutamate to glutamine?
Glutamine synthetase
Uses ATP
How many amino groups does urea have and where do these groups come from in the urea cycle?
2 groups
1st from glutamine metabolism
2nd from aspartate
Outline the urea cycle.
NH4+ + CO2 +2ATP > NH2COP(carbamoyl phosphate) + 2ADP + Pi
Carbamoyl phsophate + ornithine > citrulline
Citrulline + aspartate > arginosuccinate > fumarate + arginine
Arginine > UREA + ornithine
What are the 4 end products of nitrogen metabolism?
Urea - protein breakdown
Creatinine - creatine phosphate breakdown
Uric acid - DNA and RNA breakdown
Ammonia - control of body pH
What is hyperammonaemia?
Excess ammonia is neurotoxic.
Caused by impaired conversion of NH3 to urea due to liver failure or genetic defects (X-linked inheritance of ornithine transcarbamoylase deficiency).
Leads to cerebral oedema, coma and death.
