Nutrition Topic 4

  1. What are the 3 classifications of AA?
    Indispensable, conditionally indispensable, dispensable
  2. How is metabolic flux of amino acids determined?
    By following 'tracers'
  3. What is a nutritionally indispensable AA?
    Cannot be synthesized by the animal organism out of materials ordinarily available to the cells at a speed commensurate with the demands for normal growth
  4. Why are amino acids needed?
    • Growth
    • Nitrogen Balance
    • Plasma AA response
    • Direct AA oxidation
    • Indicator AA oxidation
    • 24h balance
    • or measure of organ or system function
  5. What are the general aspects of experimental approaches for nitrogen analysis?
    • All methods should give the same answer
    • Subjects should be studied at >6 test AA intake levels above and below requirement
    • Endpoint should show a clear response to change in test AA intake
    • Question of adaptation to test AA intake
  6. What is indicator AA oxidation (IAAO)?
    • When an indispensable AA is limiting, then all other indispensable AA wil be oxidized (remember that AA cannot be stored)
    • Increasing intake of limiting amino acid will decrease IAAO
  7. What is the minimaly invasive IAAO model?
    • Tracer administration: repeated oral 'nibbling' of tracer solution after 4h feed equilibration
    • Sampling: Breath collection for CO2 enrichment, urine in place of blood for plasma AA enrichment
    • Problem: D-AA are efficiently excreted in the urine
    • D- and L- AA can be differentiated by GCMS (gas chromatography mass spectometry) using a 'chiral column'
  8. Why is limiting AA important?
    • Vegans with lower protein intake and lower protein quality- limiting AA is significant issue especially for children
    • International- food security and diet diversity- very important especially for children
  9. What is the function of histidine requirement?
    • Histidine-free diet for 48 days, followed by repletion
    • No effect on nitrogen balance
    • Decreased protein turnover, phenelalanine oxidadation
  10. What happens when people are fed 0.6g/kg/d for 7 days?
    • Decrease in: protein turnover, albumin synthesis (negative acute phase protein), Glutathione synthesis (antioxidant capacity, increased sysceptibility to oxidative stress)
    • Increase in: Fibrinogen synthesis (positive acute phase protein)
  11. How are amino acids digested?
    • Pepsin in stomach- acidic pH
    • Proteases from pancreas in small intestine- luminal digestion
    • Peptidases on brush border of intestinal epithelial cells
    • Active transporters
  12. How does the liver play into amino acid metabolism?
    • Anabolic: constitutive protein synthesis, plasma protein synthesis, gluconeogenesis, lipogenesis
    • Catabolic: amino acid catabolism, urea cycle
  13. Synthesis of dispensible amino acids
    • High flux rates
    • High proportion from de novo synthesis
    • Synthesis accounts for 8% of basal metabolic rate
    • Ultimate precursor is gucose
    • Ultimate precursor is glucose (except for tyrosine, for cysteine only the S is from methionine)
  14. What are the issues in sulphur amino acid metabolism?
    • Methylation
    • Vitamins
    • Homocysteine
    • Liver function
    • Premature infants
    • Intravenous feeding
    • Taurine
    • Glutathione
  15. How does glutathione relate to amino acid synthesis?
    • gamma-glutamyl-cysteinyl-glycine
    • Intracellular
    • Protection agains oxidative stress- conjuction with electrophiles, removeal of ROS
    • Proteins, lipid membranes, DNA
    • Immune system function
  16. Does protein have an ergogenic effect?
    • Probably power but not endurance
    • Increased lean body mass: water, osmoregulation
    • Genes in muscle upregulating myosin, cytoskeleton, protein and glycogen synthesis
Card Set
Nutrition Topic 4
Protein and Amino acid metabolism