Nitrogen Metabolism Flashcards
What is meant by ‘negative nitrogen balance’ and when might this occur?
This is where the output of nitrogen exceeds ingestion and this can occur where there is breakdown of body protein, in fasting or in times of trauma or protein malnutrition.
Why does a balance of nitrogen need to be achieved?
As there is no real store of nitrogen in the body,
Describe the process of metabolism that occurs to ingested protein
Protein is broken down to amino acids in the gut, which then undergoes proteolysis and protein synthesis in a cyclical way to produce proteins once more. Any excess amino acids from this process are taken to the liver where they are broken down and converted into urea which is then transported to the kidneys and exreted in the urine.
What is meant by ‘essential amino acids’?
Amino acids we require because our body is incapable of making these by itself
What is meant by ‘conditional-essential amino acids’?
Amino acids of which the production can be limited by special pathophysiological conditions, such as prematurity or severe catabolic distress
What is meant by ‘non-essential amino acids’?
Amino acids which our body can make in transamination reactions, so aren’t necessary to have in our diet.
How are amino acids used by the body?
To produce nucleotides, neurotransmitters, coenzymes and melanin as well as production of glucose and ketone bodies to produce ATP
What is meant by ‘transamination’?
These reactions involve moving an amino group from one amino acid to a keto acid to form an amino acid from the keto acid and a keto acid from the amino acid (switching)
Give two examples of transamination reactions
Alanine to pyruvate.
Glutamate to alpha-ketoglutarate
What is meant by ‘glucogenic amino acids’?
Amino acids which can produce molecules which can enter the TCA cycle to produce ATP
What is meant by ‘ketogenic amino acids’?
amino acids which can produce acetyl CoA to produce ketone bodies
Why is ammonia a non-preferential molecule to have in the body?
It is toxic and quite heavily basic (so could cause metabolic alkalosis). Furthermore, ammonia can react with keto acids to form neurotransmitters which can affect body chemistry.
Why is ammonia converted to urea?
Ammonia isn’t very water-soluble so it is converted to urea to form less toxic and more water-soluble compound so less water loss is required for it to be excreted.
Name three ways in which ammonia may be produced in the body.
Microorganisms in the gut converting urea to ammonia, glutamine may be used by a fuel in some cells and produce ammonia as a product or from the breakdown of amino acids (or any molecule with an amine group generally)
Describe how ammonia is converted to urea?
Ammonia is converted to carbamoyl phosphate (by carbamoyl phosphatase) which is then converted to citrulline which enters the urea cycle. In the urea cycle citrulline combines with aspartase to produce arginosuccinate which then goes on to form arginine which then releases urea and forms ornithine which goes to reform citrulline, and the cycle continues.
