Dr. Azin Nowrouzi Tehran University of Medical Sciences

2. Many essential biomolecules contain N

3. Major Functions of NitrogenDerived from Dietary Protein

4. The nitrogen cycle No biomolecules are dedicated to the storage of N excess N is excreted N must be replenished by dietary protein

5. A. Ammonia Is Incorporated into Glutamate

6. B. Glutamine Is a Nitrogen Carrier in Many Biosynthetic Reactions

7. Assimilation of Ammonia

8. Glutamate synthatase is not present in humans. It is found in Bacteria It is used by blue-green algae and by Rhisobia. Glutamate synthetase

9. TransaminationReversible transfer of Ammonia between amino acids and ?-ketoacidsby aminotransferase Glutamate provides the amino group for the synthesis of many other amino acids through trasamination reactions

10. Aspartate Aminotransferase

11. Alanine Aminotransferase

12. Central role of the aminotrasferases and glutamate dehydrogenase in nitrogen metabolism

13. Amino Acid Synthesis The ability of an organism to live and grow is dependent on protein synthesis Therefore, a supply of all 20 aa is necessary. Higher plants are able to synthesize all 20 aas. Many microorganisms and higher animals make fewer Humans make 10 of the 20 aas (these are called nonessential amino acids. The remainder must be supplied in the diet, usually in the form of plant or animal proteins (these are called essential amino acids).

14. All 20 amino acids are essential for life, They are necessary for protein synthesis Essential or indispensable: 9 Nonessential or dispensable: 11 Review complete vs. incomplete All natural, unprocessed animal and plant foods contain all twenty amino acids A lack of any one of them leads to severe metabolic disruption and ultimate death. Metabolic Classification of the Amino Acids

15. Their synthesis depends on the availability of the appropriate carbon skeletons and a source of ammonia. Glucose is ultimately the source of carbon skeletons for most nonessential aa. Two essential aa, phenylalanine and methionine, are used to make tyrosine and cysteine, respectively. Since ammonia is available in the fed state, amino acids become essential to our diet when we are not able to synthesize their carbon skeletons. What are the nonessential amino acids synthesized from?

16. a-keto acids required for synthesis of nonessential amino acids

19. Synthesis of Tyrosine

20. Amino acids are precursors of some other biomolecules

22. Protein QualityAnimal vs. Plant protein Important in maintaining N balance Proteins have different biological value (BV) Major reasons why animal protein is called BV protein, whereas plant protein is of lower BV: Animal protein is �complete� - contains all essential amino acids Contains essential amino acids in larger amounts and in proper proportion for optimal utilization Note: Soybean protein even though from a plant, is comparable to animal protein In children leads to kwashiorker

24. Note The 56-g protein requirement for adult male can be met by 45 g of animal protein Same requirement would necessitate 65 g plant protein Combining plant products (legumes + grains) provides all essential amino acids Mixture of 30% animal protein and 70 % plant protein similar to use of animal protein alone

25. Protein RDA varies in different stages of life cycle 0-0.5 years: 1 g/lb 0.5-1 years: .71 g/lb 1-6 years: .56 g/lb 7-14 years: .45 g/lb 15-18 years: .41 g/lb 19+ years: .36 g/lb 1Ib = 0.4536 kg

27. Protein Turnover Body proteins turn over; t1/2= min - wks 400g of protein are synthesized per day and 400g are broken down Secretory proteins such as digestive enzymes, polypeptide hormones, and antibodies, turn over rapidly Structural proteins are much more metabolically stable.

28. Chemical Signals for Turnover ubiquitinatin A small, heat stable protein (ubiquitin) reacts with other proteins to mark them for destruction Oxidation of amino acid resides- Pro, Arg, Lys Pest sequences- one or more regions rich in proline (P), gltamate (E),serine (S), and threonine (T)

29. Nitrogen Balance No biomolecules are dedicated to the storage of N; Excess N is excreted. Definition: N taken in - N lost Balances Zero for healthy adults Positive childhood growth pregnancy muscle building Healing Negative for Protein malnutrition Essential aa malnutrition �stress response� (fever, recovery from surgery, etc)

30. Protein Digestion Gastric Digestion Function of pH Kills bacteria Denatures proteins� Activation and Action of Pepsin Intestinal Digestion Pancreatic enzymes Intestinal enzymes

31. Denaturation of Proteins at low pH

32. Activation of the Gastric and Pancreatic Zymogens

33. Zymogens Activation

35. Other details of Intestinal Enzymes

39. Gamma-Glutamyl Cycle A metabolic cycle for transporting amino acids into cells.

40. Disorders of Amino Acid transportation or absorption