Nitrogen Metabolism Flashcards
Which three ways must amino acids be obtained from?
1) The diet
2) de novo synthesis
3) Recovered from Protein degradation
What is the first step for catabolism?
removal of alpha-amino acid group by transamination to form Ammonia and alpha-keto acid
What is the second phase of catabolism?
alhpa-keto acids are converted to metabolic pathway intermediates such as CO2, H2O, Glucose, fatty acids of Ketone bodies
Where does some ammonia go during catabolism?
Some ammonia is lose in urine but most becomes urea
How does nitrogen leave the body?
Urea or ammonia within faeces
What is the amino acid pool supplied by?
- Amino acids from degraded body proteins
- Amino acids from dietary proteins
- Synthesis of nonessential amino acids from simple intermediates
How is the amino acid pool depleted?
- Protein synthesis
- Nitrogen-containing molecule precursors
- Conversion to glucose, glycogen, fatty acids and ketone bodies
What is protein turnover?
The amount of protein hydrolysed and resynthesised each day
How is protein degraded?
- ATP dependent ubiquitin-proteasome system (endogenous proteins)
- ATP independent enzyme system of the lysosome (extracellular proteins)
What is the ubiquitin-proteasome proteolytic pathway?
Ubiquination is linkage of ubiquitin’s alpha-carboxyl group to amino group of lysine
the degradation is determined by the oxidation levels and PEST sequences
How does protein digestion occur?
Degraded by enzymes produced in stomach, pancreas & small intestine
Stomach secretes gastric juices containing:
- Hydrochloric acid (denatures proteins)
- Pepsin (acid-stable endopeptidase that releases amino acids and peptides)
Pancreas produces proteases: -Varying specificity for amino acid R-groups
Small intestine contains aminopeptidases (exopeptidases) which cleave at N-terminal residues to produce smaller peptides & free amino acids
Free amino acids are taken in by Na+ linked secondary transport system
Di- & Tri-peptides are taken in by H+ linked transport of hydrolysed into amino acids in the cytosol then released by facilitated diffusion
How many transport systems exist for amino acids?
7
What is transamination?
Amino group transferal to glutamate which can be oxidatively deaminated or used as an amino group donor so it is called a non-essential amino acid synthesis
Where are aminotransferases found and how are they involved in nitrogen removal?
- found in cytosol and mitochondria of liver, kidney, intestine and muscle
- Transfer amino groups and each aminotransferase is specific to one or a few amino group donors
- Equilibrium close to 1 therefore reversible
What is oxidative deamination?
results in amino group release as ammonia which occurs in the liver or kidney
-also creates alpha-keto acids to enter energy metabolism
