Nitrogen metabolism Flashcards
Where does nitrogen come from?
Protein from the diet
How is nitrogen stored?
It is not. Proteins are always being broken down and used, never stored. Body should always be in nitrogen balance
Uses for amino acids
Make protein Amino acids DNA glucose Neurotransmitters Melanin
Name the two categories of amino acids
Essential (need to consume) Non essential (conditional to bodies needs at the time)
Which co-enzyme is very important in all reactions of amino acid metabolism? Where does it come from?
pyridoxal phosphate
Vitamine B6
What can Tyrosine (phenylalanine) be metabolised to?
Melanine Dopamine Adrenaline Noradrenaline thyroxine
What can Tryptophan be metabolised to?
Seratonin
Melatonin
What can Arginine be metabolised to?
Nitric oxide
What can Histidine be metabolised to?
Histamine
Function of the amino acids glycine, glutamate and aspartate?
Neurotransmitters
What is transamination?
What catalysis it?
When new amino acids are made by adding side chains to the carbon skeletal of other amino acids
Enzyme- Transaminase (liver)
What are Glucogenic amino acids? Give examaples
Amino acids which can be converted into glucose by gluconeogenesis and can feed into the TCA cycle as pyruvate or one of intermediates.
Alanine, glycine, tryptophan
What are ketogenic amino acids? Give examples
can be converted to ketone bodies and feed TCA cycle mostly by being converted to acetyl coA or acetylacetate.
Asparate, lysine, leucine, tyrosine, glutamate
Which amino acid is both Glucogenic and ketogenic?
Threonine
How is ammonia generated?
During reactions which produce TCA intermediates, the amino group no longer needed given off as ammonia
How is ammonia removed?
It is toxic to the body
Excreted as urea in the urea cycle
Describe the outcomes of the metabolites of glutamate
- In the muscle some of the amino acids like glutamate are converted to alanine which is exported to the liver in a process to make alpha-ketoglutarate
- If you break down the glutamate to make glutamine you generate ammonia and some of that is send via the blood to the liver and some is sent directly to the kidney for excretion
Glutamate and ammonia
. Glutamate + ammonia can be used to make glutamine in a reaction that requires ATP with a synthatase enzyme. Glutamine can be converted back to glutamate when the need arises and releases ammonia again
Functions of glutamine and its metabolites
- Important source of fuel during fasting particularly in muscles, immune cells
- For gluconeogenesis, particularly in the kidney.
- Produces ammonia that can acts as a buffer for protons (removed in urea)
- As glutamate – important neurotransmitter.
- Anti-inflammatory properties – in gut
What are the different sources of ammonia?
- Microflora in gut release ammonia when breaking down food
- Transamination of AA (glutamine).
- Breakdown of DNA/RNA
- Metabolism of AA (glutamate recycling in the liver – dehydrogenase).
- Ketogenesis/gluconeogenesis from AA releases ammonia.
Describe main features of the urea cycle in the liver
Requires amino groups from aspartate and ammonia
Regulatory enzyme is CP synthase
2ATP required
Controlled allosterically by a metabolit of glutamate, N-acetyl glutamate, formed when there is an excess of glutamate so drives urea cycle.
Glutamate + acetyl-coA—- N-acetylglutamate + CoASH
Causes of possible defects in Urea formation?
Regulated by 6 enzymes, defects of any of which will cause reduction in urine formation
Symptoms of ammonia accumulation?
vomiting, nausea, neurological disorders, lethargy, coma.
Two types of onset – neonatal —late-onset (post-natal; 70%)
Treatment of ammonia onset
Dietary management and phenylbutyrate (ammonia scavengers)
