Protein And Amino Acid Metabolism Flashcards
(33 cards)
What happens to glucoagonic amino acids that are obtained from diet? give an example of one
contribute to gluconeogenesis and input into krebs cycle at many levels
eg tyrosine
What happens to ketogenic amino acids? give an example of one
converted to ketone bodies and used for energy also
eg lysine and leucine
What outputs and stores at there of N containing compounds?
stores: - body proteins (2kg) - amino acid poos (16g) - n containing compounds (50g) outputs: - loss in hair, skin, nails, faces, urine
What happens to the amino group from amino acids?
converted to ammonia and excreted
When are protein reserves used for energy? What hormones promote degradation over synthesis and vica versa?
Only used in extream starvation
Insulin and growth hormone promote protein synthesis
Glucocorticosteroids and coritisol increase protein degradation
Where does the carbon skeleton and amino group come from for amino acid synthesis?
carbon- glycolysis, pentose phosphate pathway, krebs intermediates
amino- provided by other amino acids by transamination or from ammonia
Why are amino acids synthesised?
- protein synthesis
- neurotransmitters (serotonin from tryptophan, GABA from glutamate, NO from arginine)
- chemical signals (histamine from histidine, catecholamines from tyrosine)
- Heam
- creatinine ect all derive from amino acids
What is transamination?
move the amine from one amino acid onto a ketoacid to create a new amino acid which can more easily be turned into urea and a new keto acid
How do most aminotransferases work?
by moving the amino group from one amino acid onto alpha keto- gluterate to produce glutamate
what does aspartate amino transferase do?
moves an amine group onto oxaloacetate to make an aspartate- needed in urea cycle
What vitamin is needed for transamination?
A B6 derivative- pyridoxal phosphate
What two amino transferases are released on injury to hepatocytes, what is their role?
alanine aminotransferase (ALT)- alanine into glutamate Aspartate amino transferase (AST)- converts amino group of glutamate into oxaloacetate to make aspartate
When and where does deamination (liberating amino group as free ammonia rather than transamination) done?
in liver and kidneys
done when D- amino acids are digested from some foods (normal isomer is L- amino acids)
Where does the urea cycle occur??
liver
How is urea cycle controlled?
By expression of enzymes in urea cycle- high protein diet= high expression
Why does ammonia toxicity occur in refeeding syndrome?
They go from very low protein diet (so low expression of urea cycle enzymes) to very high protein, but expression of the enzymes cannot increase fast enough to meet new demands of ammonia removal
What inputs are there to the urea cycle?
glutamate, aspartate (all glutamate converted to aspartate by AST in first step), CO2, NH3, H20 and ATP
What symptoms come with defects in urea cycle?
basically NH3 toxicity
severe disorders presents within 1 day of birth
mild may present in early childhood
vomiting, lethargy, irritability, mental retardation, seizures, coma
What determines the severity of a urea cycle defect?
- Which of the 5 enzymes are absent
- How much the function of the enzymes is effected
- amount of protein eaten
How is a urea cycle defect managed?
- low protein diet
- replace amino acids in diet with keto acids
What effects does high ammonia have to body?
- diffuses into brain and is toxic
- interferes with amino acid transport and synthesis
- interferes with metabolism of neurotransmitters
- increases blood pH
- disrupts cerebral blood flow
- alters blood brain barrier
- interferes with krebs cycle
What is normal blood conc of NH3?
25-40umol/L
How is NH3 safely transported to liver and kidneys?
- Combine with glutamate to form glutamine to take it to liver/ kidneys where it is is reformed and fed into urea cycle
- Combine with pyruvate to form alanine which takes it to liver where transamination makes it into glutamate and pyruvate
What is creatinine a clinical marker of?
- it is a breakdown product of creatine and creatine phosphate
- usually produced at constant rate (and is proportional to muscle mass), elevated when:
- exceedingly high muscle mass
- muscle atrophy
- damage to nephrons
