2. Protein And Amino Acid Metabolism Flashcards
What are the major and minor nitrogen containing compounds?
Major: amino acids, proteins, purines and pyrimidines
Minor: porphyrins, creatine phosphate, neurotransmitters
What is creatinine?
Breakdown product of creatine and creatine phosphate
Produced at constant rate depending on muscle mass
Provides estimate of muscle mass - creatinine urine excretion over 24h proportional to muscle mass
What is N equilibrium?
Intake = output
No change in total body protein
Normal state in adult
What is positive N balance?
Intake > output
Increase in total body protein
Normal state in growth and pregnancy or in adult recovering from malnutrition
What is negative N balance?
Intake < output
Net loss of body protein
Never normal
Causes include trauma, infection or malnutrition
Name a glycogenic amino acid and a ketogenic amino acid
Glucogenic - alanine
Ketogenic - lysine
Name an amino acid that is both glucogenic and ketogenic
Tyrosine
What happens in Cushing’s syndrome?
Excessive breakdown of protein fur to excess cortisol
Weakens skin structure leading to striae formation (stretch marks)
What extra amino acids do children and oregano women require in their diet?
Arginine
Tyrosine
Cysteine
Where do carbon atoms for non-essential amino acid synthesis come from?
Intermediates of glycolysis
Pentose phosphate pathway
Krebs cycle
Why is removal of amino group from amino acid essential?
To allow carbon skeleton of amino acids to be until I see in oxidative metabolism
What are the 2 main pathways that facilitate removal of nitrogen form amino acids?
Transamination
Deamination
What is transamination?
amino acid 1 + keto acid 2 amino acid 2 + keto acid 1
Transfer of the amine group of an amino acid with the oxygen of a keto acid
Most amino acids are converted to glutamate and some to aspartate
What do most aminotransferase enzymes use?
What is the exception?
Alpha-ketoglutarate to funnel amino group to glutamate
Exception: aspartate aminotransferase uses oxaloacetate to funnel amino group to aspartate
What do all aminotransferase require?
Coenzyme pyridoxal phosphate which is a derivative of vitamin B6
What are ALt and AST and what do they do?
ALT - alanine aminotransferase, converts alanine to glutamate
AST - aspartate aminotransferase, converts glutamate to aspartate
What can plasma ALR and AST levels show?
Measures as part of liver function test
Levels particularly high in conditions that cause extensive cellular necrosis such as: viral hepatitis, autoimmune liver disease, toxic injury
What is deamination?
Liberates amino group as free ammonia
Mainly occurs in liver and kidney
Also important in deamination of dietary D-amino acids
Name the enzymes that can deamination amino acids
Amino acid oxidases
Glutaminase
Glutamate dehydrogenase
Describe features of the urea cycle
Occurs in liver
Involves 5 enzymes
Amount of urea cycle enzymes relate to need to dispose of ammonia
High protein diet induce enzyme levels
Low protein diet or starvation represses levels
What is refeeding syndrome?
Can occur when nutritional support given to severely malnourished patients
Ammonia toxicity significant factor
What defects can occur in the urea cycle?
Autosomal recessive geneticist disorders caused by deficiency of one of enzymes in urea cycle
Mutations cause a atrial loss of enzyme function
What can defects in the urea cycle lead to?
Hyperammonaemia
Accumulation/excretion of urea cycle intermediates
When do severe urea cycle disorders present?
Show symptoms within 1 day after birth, can lead to death if left untreated
