Amino Acid/Nitrogen Metabolism Flashcards
Use of circulating amino acids
Amino acids can be used for protein synthesis.
Amino acids can be used for the synthesis of other nitrogen containing molecules in the body (examples include: neurotransmitters, nucleotides, and heme).
Are amino acids stored in the body?
Amino acids are not stored within the human body.
Excess amino acids beyond those needed for the purposes outlined above and to maintain basal levels of amino acids within the body are catabolized.
In what form is nitrogen excreted
Nitrogen from excess amino acids is detoxified and eliminated from the body as urea
How are amino acids used during a fast
During a fast, amino acids are derived from the breakdown of cellular proteins.
Carbon skeletons derived from amino acids are used:
for gluconeogenesis or ketogenesis.
as a source of energy
What is positive nitrogen balance
Individuals synthesizing net muscle mass can be in positive nitrogen balance: with more nitrogen coming into and staying within the body than is being eliminated (body builders, pregnant women, individuals recovering from injury).
What is negative nitrogen balance
Individuals excreting more nitrogen than they are taking in.
Negative nitrogen balance is typically associated with net destruction of muscle/tissue protein for the reasons outlined below.
Causes of negative nitrogen balance
Metabolic stress: increased tissue protein catabolism associated with physiologic changes to combat various forms of stress.
Trauma, surgery, burns, and wasting diseases, situations where there is net tissue destruction can result in negative nitrogen balance.
Inadequate dietary protein (energy): increased tissue protein breakdown to provide amino acid precursors for protein synthesis, energy and gluconeogenesis.
Lack of one or more essential amino acids: increased tissue breakdown to provide amino acid precursors for new protein synthesis and other anabolic reactions.
What are essential amino acids
Of the 20 common amino acids, only 11 can be made within the human body, the other 9 must be obtained from the diet.
Amino acids that must be taken in from the diet are referred to as essential amino acids.
What are the essential amino acids
PVT TIM HALL
Arginine not for healthy adults (only children)
What impacts the quality of protein
The quality of proteins in the diet relates to their content of essential amino acids and digestibility.
What is Kwashiorkor
Kwashiorkor is due to an inadequate intake of high quality protein.
Characteristic clinical signs include:
edema (caused by degradation of albumin to maintain amino acid pools for the synthesis of essential proteins)
growth failure
dermatological problems
lethargy
irritability
Children with kwashiorkor also have enlarged, fatty livers (because of the loss of hepatic ApoB100 and the inability to transport VLDL to adipose) and subcutaneous fat, which distinguishes kwashiorkor from marasmus.
What is Marasmus
marasmus is a consequence of caloric insufficiency.
Marasmus is characterized by generalized wasting including atrophy of muscle and subcutaneous tissues.
Because of the caloric insufficiency seen in marasmus, these individuals do not have subcutaneous fat.
What causes death in Kashiorkor and marasmus (Protein-Energy Malnutrition {PEM})
infection associated with decreased immune function.
Monitoring of PEM
Protein-energy malnutrition can delay wound healing and make patients more susceptible to infections.
Evidence of PEM can be obtained by serum protein profiles.
Early detection can best be achieved by monitoring an abundant serum protein with a short half life.
Transthyretin is a sensitive indicator of protein deficiency and is also used to monitor the effectiveness of nutritional therapies to reverse PEM.
What amino acid does corn have in low amounts
Lysine
Protein breakdown in the fed state
Proteins are broken down to peptides and amino acids in the GI tract and once absorbed, amino acids enter the portal circulation to the liver.
Here amino acids can enter the liver to meet the liver’s needs for the synthesis of proteins and other nitrogen-containing compounds.
Excess amino acids can also be taken into the liver and catabolized.
When the carbon skeletons of amino acids are used for energy or fat synthesis in the fed state, the nitrogen is removed and must be detoxified by conversion to urea.
Amino acids also exit the liver to the general circulation where they are used by other tissues for protein synthesis and other purposes.
Process of using amino acids for protein synthesus during a fasting state
In the fasted state, at least during a prolonged fast, an important role for amino acids is in providing carbon skeletons to the liver for gluconeogenesis to maintain blood glucose levels.
Muscle protein is broken down to individual amino acids, which funnel their carbon skeletons into alanine.
Once in the liver, alanine is converted to pyruvate.
The nitrogen from alanine (given up during the conversion to pyruvate) will ultimately be detoxified and eliminated from the body as urea.
Glutamine is also released from the muscle and its side chain nitrogen can be used for nucleotide production in cells lining the GI tract or be used by the kidney to soak up protons. Either of these tissues take up glutamine and release alanine, which ultimately finds its way to the liver for gluconeogenesis and urea production.
In smaller amounts, other amino acids can be transferred from muscle to the liver, particularly branched chain amino acids, some of which can be used for gluconeogenesis.
The carbon skeletons of each of the branched chain amino acids can also be used for energy or ketone body formation.
Describe transamination reaction
In a transamination reaction (Fig. 11), amino acid1 transfers its amino group to alpha-keto acid2 forming amino acid2, while at the same time generating alpha-keto acid1.
Alpha-keto acid2 and amino acid2 in transamination reactions are typically alpha-keto glutarate and glutamic acid, respectively
Process of alanine transformation in the liver
Alanine is transported from muscle to liver to provide carbons for gluconeogenesis.
Once in the liver alanine is transaminated by alanine transaminase (ALT) to pyruvate, which can go on to form glucose.
The amino group of alanine is handed over to alpha-ketoglutarate to form glutamate
Glutamate can give up its amino group in two ways, each creating a form of nitrogen that can enter the urea cycle for detoxification.
- The first is the glutamate dehydrogenase reaction, which forms ammonia.
This ammonia can directly enter into the urea cycle.
- Glutamate can also transfer its nitrogen to oxaloacetate forming aspartic acid in a transamination reaction catalyzed by aspartate transaminase (AST).
The aspartic acid so formed can also directly enter the urea cycle.
