Flashcards in 9. Protein and Amino Acid Metabolism Deck (43)
What is creatinine the breakdown product of?
Creatine and Creatine phosphate in the muscle.
How is creatinine link to muscle mass.
The amount excreted is proportional to muscle mass so provides an estimate of muscle mass.
What can creatinine be used as a clinical marker for?
Muscle mass and kidney function.
What contributes to intake of nitrogen?
What contributes to the output of nitrogen?
Loss of skin, hair, nail and N-waste product in faeces and urine.
Where is nitrogen stored in the body?
Amino acid pool and N-containing compounds.
What is N equilibrium and what are the implications on body protein and health?
Where input= output. No change in body protein and normal healthy state in adults.
What is positive N balance and what are the implications on body protein and health?
Intake > output. There's an increase in body protein, there is normal health in growth and pregnancy or in adults recovering from malnutrition.
What is negative N balance and what are the implications on body protein and health?
What are the three routes an amino acid can go down to produce energy?
Glucogenic, ketogenic or both glucogenic and ketogenic.
What is one example of a glucogenic amino acid?
Alanine, glycine, cysteine, serine, arginine, proline, histidine, glutamine, glutamate, methionine, valine, aspartate, asparagine.
What is one example of a ketogenic amino acid?
Lysine or leucine.
What is an example of a glucogenic/ketogenic amino acid?
Treonine, tryptophan, tyrosine, phenyalanine or isoleucine.
When are protein reserves metabolised?
Under extreme stress, starvation.
How is protein reserve metabolism regulated?
By hormonal control. Insulin and growth hormone decrease protein degradation but glucocorticoids increase protein degradation.
What can excessive breakdown of protein occur in?
Cushing's syndrome, can lead to striae formation.
What are the nine essential amino acids?
Why is it essential that vegetarian diets have a wide variety of plant sources?
Because, unlike meat, proteins of plant origin are deficient in at least one essential amino acid so to obtain all essential amino acids, there must be a variety of plant proteins eaten.
Where do carbon atoms for non-essential amino acid synthesis come from?
Intermediates of glycolysis, pentose phosphate pathway or Kreb's cycle.
What two main pathways facilitate removal of nitrogen from amino acids?
Transamination and deamination.
What happens in transamination?
The R group from an amino acid and a keto acid swap over. Normally a-ketoglutarate is used to funnel the amino group to glutamate. But aspartate amino transferase uses oxaloacetate to funnel amino group to aspartate. The coenzyme pyridoxal phosphate is required.
What are two key aminotransferase enzymes?
Alanine aminotransferase (converts alanine to glutamate) and aspartate aminotransferase (converts glutamate to aspartate).
What happens in deamination?
The amino acid group is released as free ammonia, mainly happens in the liver and kidney.
What happens to the ammonia produced in deamination?
It is converted to urea or excreted directly in urine.
What enzymes can deaminate amino acids?
Amino acid oxidases, glutaminase and glutamate dehydrogenase.
What are some factors of urea?
High nitrogen content, non-toxic, water soluble, chemically inert in humans, excreted in urine and has an osmotic role in kidney tubules.
Where does the urea cycle take place?
In the liver.
How is the urea cycle controlled?
By the amount of substrate available. High protein induces enzyme levels, low protein represses levels. The cycle is induced, not regulated.
Why must refeeding be done gradually?
Because sudden high levels will lead to ammonia toxicity as the urea cycle won't be up regulated quickly enough.