lecture 12 - nitrogen metabolism Flashcards
What are the sources of nitrogen in the body?
Dietary protein, natural protein turnover/body protein
What are the uses of nitrogen in the body?
Neurotransmitters, coenzymes, amino acids/proteins, nucleotides
What is the main form that nitrogen is in in the body?
Part of amino acids
What is the difference between essential and non-essential amino acids?
The body can make non-essentials, but cannot make essentials so they need to be extracted from the diet
What are conditionally essential amino acids, and what is the key example?
The body can synthesise them, however cannot make adequate amounts so require dietary top up in certain circumstances. Key example is arginine, which needs dietary supplementation during periods of growth.
What is nitrogen balance dependent on?
Dietary nitrogen intake,
Physiological state
What is the default state of nitrogen balance?
In balance - nitrogen intake and excretion are equal
What are some causes of a positive nitrogen balance?
Growth of lean mass - Childhood/adolescent growth, pregnancy, body building
What are causes of a negative nitrogen balance?
Starvation, illness (e.g. sepsis), burns, trauma
What are the metabolic fates of amino acid carbon skeletons?
Skeletons are either glucagenic or ketogenic - form ketone bodies or glucose
What form is nitrogen stored as waste product?
Urea
Where is urea synthesised?
In the periportal hepatocytes of the liver
Which 2 amino groups are used in nitrogen excretion?
Glutamine and alanine
How is glutamine involved in nitrogen excretion?
- In tissues, an additional amino group (NH3) can be added to glutamate via glutamine synthetase to form glutamine.
- This stores more nitrogen, until the molecule reaches the liver where glutamine is converted back to glutamate via glutaminase
- NH3 is released for conversion to urea then excretion.
What enzyme converts glutamate to glutamine?
Glutamine synthetase
What enzyme converts glutamine to glutamate?
Glutaminase
What process occurs in periportal hepatocytes?
Glutamine is converted to glutamate via glutaminase, releasing an NH3 which is fed into the urea cycle
What process occurs in perivenous hepatocytes?
Excess ammonia is captured by converting glutamate to glutamine, so that NH3 is not released into the circulation once it leaves the liver.
What enzyme is required to remove an amino group from glutamate?
Glutamate dehydrogenase
What is a transamination reaction?
Transferring an amino group from one amino acid to a keto acid, forming a new amino acid and the corresponding keto acid.
What enzymes are required for transamination reactions?
Aminotransferases
What is Phenylketonuria (PKU)?
A genetic phenylalanine hydroxylase enzyme deficiency
What is the pathophysiology of PKU?
The deficiency in Phenylalanine hydroxylase prevents conversion of Phenylalanine to Tyrosine, leading to a build up of Phenylalanine and other toxic metabolites in the blood, and a deficiency of tyrosine
What are the symptoms of PKU?
seizures, hair/skin hypopigmentation, intellectual disability, musty odour
