Protein Metabolism And Nitrogen Flashcards
In adults, Nitrogen is normally kept in balance. If 16g is the daily dietary intake, what is the N loss?
~2g is lost as body proteins (skin,hair,nails)
~14g is lost in waste products faeces and urine.
What is meant by a +ve nitrogen balance?
This is where intake exceeds output. This is normal when there is an increase in body protein such as in pregnancy and childhood.
What are common causes of a negative nitrogen balance?
Negative nitrogen balances are never normal, and this is when there is a loss in body protein. This can be caused by trauma, infection or malnutrition.
How can the carbon skeleton of amino acids be classified and how does each lead to energy production?
Ketogenic - leads to production of ketone bodies
Glucogenic - leads to gluconeogenesis in the liver –> glucose.
In addition to the nine essential amino acids, which other 3 amino acids are important for pregnant women and children?
Arginine, cysteine, tyrosine.
In amino acid synthesis, where does the amine group come from?
Either from ammonia or transamination.
What is the generalised equation for a transamination reaction?
Amino Acid A + Keto acid B –> Amino Acid B + Keto acid A
What is the name of the enzymes which catalyse a transamination reaction?
Amino transferase.
State the three enzymes which can deaminate amino acids.
Amino acid oxidases, glutaminase, glutamate dehydrogenase.
In deamination, where does the amine group get moved from the amino acid too?
The amine group becomes free ammonia. Because ammonia and ammonium ions are both very toxic these must be removed quickly from the body.
Give properties of urea.
Urea has a high nitrogen content and is non toxic. It is excreted in the urine via the kidneys and has osmotic properties due to its soluble nature. It is inert in humans and is not broken down.
What two amino acids are fed into the urea cycle?
Aspartate and Glutamate.
Where does the urea cycle occur and how is it altered by changes in quantity of protein in diet?
It takes place in the liver.
When protein in diet increases, amino acids increase and therefore more enzymes are needed to dispose of ammonia. A low protein diet suppresses the enzymes.
Is the urea cycle regulated?
No, it is only induced.
What is refeeding syndrome?
Refeeding syndrome is when a person has had a low level of protein intake for a long time so when they intake protein at a normal level they do not have sufficient enzymes to cope with this and toxic levels of ammonia build up.
