1. Lecture 6- 24 October 2013 Most of this lecture taken from Chapters 6,7 of Rolfes et al(Understanding Normal and Clinical Nutrition (Nutrition 2104/2106 text)

2. Lecture 6- 24 October 2013 Protein metabolism and regulation

3. Outline of lecture 6 Amino acids Definition of amino acid Structure of amino acid Non-essential amino acids Essential amino acids Conditionally essential amino acids Class exercise

4. Outline of lecture 6 Proteins Definition of protein Amino acid chains Amino acid sequence Protein shapes Protein functions Protein denaturation Digestion Absorption Transport

5. Outline of lecture 6 Metabolism Amino acid anabolism Protein anabolism Protein catabolism Amino acid catabolism Nitrogen balance Regulation of amino acid and protein metabolism

6. More detailed comments

7. Amino acids Definition of amino acid -building blocks of proteins Structure of amino acid -each amino acid has an amino group(NH 2 ), an acid group(COOH), a hydrogen atom, and a distinctive side group all of which are attached to central carbon atom -some amino acids also contain sulphur

8. Amino acids Non-essential amino acids -body can synthesise these for itself -foods usually deliver these to the body but it is not essential for food to deliver these amino acids-usually

9. Amino acids Essential amino acids -cannot make on own or cannot make sufficient amounts of these amino acids -therefore they are required in the diet

10. Amino acids Conditionally essential amino acids -sometimes a non-essential amino acid becomes essential -two reasons for conditional essentiality

11. Class exercise -find all essential amino acids -find all non-essential amino acids -find an example of a conditionally essential amino acid -what foods contain all essential amino acids? -what foods are lacking in one or more essential amino acids? -how does one overcome issue of diet lacking in one or more essential amino acids?

12. Class exercise Essential amino acids Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine

13. Class exercise Non- Essential amino acids Alanine Arginine Asparagine Aspartic acid Cysteine Glutamic acid Glutamine Glycine Proline Serine Tyrosine

14. Class exercise Conditionally Essential amino acids Phenylalanine makes tyrosine If not enough phenylalanine in diet or conversion is reduced then tyrosine becomes essential

15. Proteins Definition of protein -compounds composed of carbon, hydrogen, oxygen, nitrogen and sometimes sulphur atoms, arranged into amino acids linked in a chain

16. Proteins Amino acid chains -dipeptides, tripeptides, polypeptides

17. Proteins Amino acid sequence -20 amino acids give tremendous variability unlike starch

18. Proteins -Protein shapes -side groups- attract or repel water -attract or repel other side groups on amino acids in amino acid sequence

19. Proteins Protein denaturation -if change protein structure lose function

20. Proteins Digestion mouth-no digestion stomach-acid digestion leads to denaturation -acid converts pepsinogen to pepsin -pepsin makes large polypeptides into smaller polypeptides and some amino acids

21. Proteins Digestion small intestine-pancreatic and intestinal proteases digest polypeptides to: oligopeptides ( oligo means few; one definition suggests 2-40 amino acids though this definition varies), tripeptides, dipeptides and amino acids -peptidases split most of dipeptides and tripeptides to single amino acids

22. Proteins Digestibility Proteins vary in their digestibility due to variable dietary protein structures as well as other food ingredients and hence accessibility to protein digestive enzyme active sites Animal proteins are generally very digestible and plant proteins are generally less digestible than animal proteins Complete plant proteins -soy - very digestible - close to many animal proteins’ digestibility -quinoa - about 10 % less digestible than soy

23. Proteins Digestibility Digestibility affects availability (WWFQ) of essential and non-essential and conditionally essential amino acids

24. Proteins Digestibility Current gold standard for protein digestibility is: Protein Digestibility Corrected Amino Acid Score (PDCAAS) PDCAAS = mg of limiting amino acid in 1 g of test protein / mg of same amino acid in 1 g of reference protein) x true digestibility percentage. True digestibility = human digestibility - faecal digestibility e.g. of reference protein = milk protein = 100

25. Proteins Digestibility FAO has recently proposed a new gold standard for protein digestibility -Digestible Indispensable Amino Acid Score (DIAAS) DIAAS % = 100 x [(mg of digestible indispensable amino acid in 1 g of dietary protein)/(mg of the same indispensable amino acid in 1 g of reference protein)]

26. Proteins Absorption -specific carriers move amino acids and a few dipeptides and tripeptides into intestinal cells -once inside intestinal cells amino acids can be used for energy or to synthesise some proteins

27. Proteins Transport -rest of amino acids put directly into blood and taken to liver -are amino acid carriers required for free amino acids to transport those free amino acids in the blood?

28. Proteins Class exercise -what happens to protein functions if there are insufficient: a) essential amino acids in the diet? why? b) non-essential amino acids in the diet? Explain -what happens to protein functions if there are sufficient? c) essential amino acids in the diet? explain

29. Metabolism Protein anabolism amino acids joined to amino acids figure 6-7 Rolfes et al

30. Fig. 6-7, p. 188

32. Metabolism Protein catabolism -digestion in stomach and small intestine -non gi tract catabolism

33. Metabolism Amino acid catabolism -figure 7-13 Rolfes -figure 7.24 Gropper - get urea which is excreted in urine

34. © 2009 Cengage - Wadsworth

36. Metabolism Nitrogen balance -equilibrium N in = N out healthy adult -negative nitrogen balance N in < N out illness, starvation -positive nitrogen balance N in > N out -person recovering from illness -growing child

37. Regulation of amino acid and protein metabolism -demand for amino acid and protein anabolism -eg if need positive N balance or to keep in N equilibrium -if lots of glucose available -demand for amino acid and protein catabolism-eg if in negative N balance or to keep in N equilibrium -if short of glucose

38. Relation of protein metabolism to carbohydrate and lipid metabolism -figure 7-8 Rolfes et al.

39. © 2009 Cengage - Wadsworth

40. Class exercise Explain the importance of dietary carbohydrate to protein metabolism Explain the importance of dietary lipid to protein metabolism Explain the importance of dietary protein to protein metabolism