Food

1. Food • Why food? • Our body performs many processes and has necessary infra-structure for this performance • Energy is needed to • Perform these processes • Build necessary infra-structure • Sustain the molecular organization • Food provides this much needed energy Aminoacids

2. What is food • Food consists of six basic ingredients • Carbohydrates • Lipids • Proteins • Vitamines • Minerals • Water Aminoacids

3. Carbohydrates • Include sugars and sugar polymers (starch and glycogen) etc. • Generally used for generation of energy • Some role in structure • Polymeric forms undergo digestion Aminoacids

4. Lipids • Include oils and fats etc • Second most preferred source of energy after carbohydrates • Some structural role e.g. biomembranes • Undergo digestion Aminoacids

5. Proteins • Undergo digestion to split into aminoacids • The least preferred role in energy generation • Perform a large number of roles, however, major role in structure and catalysis Aminoacids

6. Vitamins • Cofactors for many enzymes • No role as energy substrate • No digestion (directly absorbed) Aminoacids

7. Minerals • Major role chemical reactions particularly oxidation/reduction reactions • No digestion, directly absorbed Aminoacids

8. Water • Serve as solvent • No digestion, directly absorbed Aminoacids

9. Proteins • Proteins are made up of 20 different types of aminoacids • Dietary proteins are digested to yield aminoacids • These aminoacids are absorbed by the intestine and transferred to blood stream • Aminoacids enter into different body cells from blood circulation • In cells, aminoacids are then bonded together to from specific proteins (tissue /species specific) • These proteins then perform various but important functions of the cell/body Aminoacids

10. Aminoacids Aminoacids

11. Types of Aminoacids • Protein & Non-protein aminoacids(Standard & Non-standard aminoacids) • Protein Aminoacids are further classified on the basis of • The nature of their side chains • Polar or non-polar • Aromatic or non-aromatic • Function groups (hydroxyl, thio, methyl-thio) • Capability of Synthesis (Essential or Non-essential) Aminoacids

12. Definition • Organic compounds containing an amino and a carboxylic acid Aminoacids

13. Building Blocks of Proteins • Amino acids are the building blocks of proteins • There are 20 different aminoacids used for proteins synthesis in all living organisms • An α-amino acid consists of a • central carbon atom, called the αcarbon, linked to • an amino group, the αamino group • a carboxylic acid group, the α carboxylic group • a hydrogen atom, and • a distinctive R group called the side chain. Aminoacids

14. Amino acid Isomers • With four different groups α-amino acids are chiral (except glycine) • forms two mirror-image forms the L isomer and the D isomer Aminoacids

15. Ionization of Amino Acids • Only L amino acids are used in proteins • Aminoacids are ionized in solution Aminoacids

16. Ionization of Amino Acids • At acidic pH • Amino group is protonated (NH3+) • Carboxyl group is not deprotonated (COOH) • At neutral pH • Amino group is protonated (NH3+) • Carboxyl group is deprotonated (COO_) • At basic pH • Amino group is not protonated (NH2) • Carboxyl group is deprotonated (COO_) Aminoacids

17. General Formula of an Amino Acid R= -H, -CH2, -CH2OH, C2H4OH etc Aminoacids

18. Side Chain Variations • Size • Shape • Charge • hydrogen-bonding capacity • hydrophobic character • chemical reactivity Aminoacids

19. Classification of Amino Acids Aminoacids

20. Uncharged (Non-Polar) Amino Acids Aminoacids

21. Glycine • Simplest amino acid • Side chain only a H atom • A chiral (optically inactive) Aminoacids

22. Physiological Roles-Glycine • Part of tripeptide coenzyme “Glutathione”, which protects –SH group from oxidation • Takes part in synthesis of heme, purines and creatin • Detoxication of benzoic acid to make a soluble conjugate, the hippuric acid • Formation of bile salts by conjugation to cholic acid (glyocholic acid and glycochenodeoxycholic acid) • Can be converted to other aminoacids e.g. serine, which may be converted to pyruvate (glucogenic aminoacid) • Glycine oxidase conver glycine into glyoxalic acid, which is oxidized to form formic acid and oxalic acid • Formic acid becomes a part of 1-carbon metabolism • Oxalic acid is excreted in urine • Excess formation leads to “Hyperoxalurea” resulting in formation of Ca-oxalate which precipitates in urinary tract • Precipitation results in Urinary Calculi and Calcification of kidneys. Aminoacids

23. Non-Polar Amino Acids • Progressively larger side chains • Isoleucine contains an additional chiral center • Stabilize protein structure in aqueous solutions Aminoacids

24. Physiological Roles-Valine • Undergoes • transamination followed by • decarboxylation • This results in the formation of • isobytyryl-CoA ultimately converted into • Succenyl-Co-A, an intermediate of TCA cycle Aminoacids

25. Physiological Roles-Leucine • Undergoes oxidative transamination to ultimately form • HMG-CoA • HMG-CoA may be converted into • Cholysterol • Acetoacetate/Acetyl-CoA (so a ketogenic aminoacid) Aminoacids

26. Physiological Roles-Isoleucine • Undergoes oxidative transamination to form • HMG-CoA • HMG-CoA may be converted into • Cholysterol • Acetoacetate/Acetyl-CoA (so a ketogenic aminoacid) Aminoacids

27. Proline • Imino acid • Heterocyclic: contains a pyrrole ring (pyrrolidine derivative) • Side chain bonded to αaminogroup • Causes bends in protein structure • May form 4 hydroxyproline as a result of post-transcriptional modification perhaps only in collagen • A small proportion may also occur as 3-hydroxyproline too • Interchangeable with ornithine, thus it can contribute to urea cycle • Can give rise to glutamate Aminoacids

28. Sulfur Containing Amino Acids • Met is always first amino acid of a nascent protein • Cys may be involved in forming disulfide bridges Aminoacids

29. Sulfur Containing Amino Acids • A disulfide bridges between to cysteines to form a Cytine Aminoacids

30. Aromatic Non-polar Amino Acids • Phe is purely hydrophobic but Try is less so • Strongly absorb UV light (Amax 280λ) Aminoacids

31. Phenylketonurea • It is an autosomal recessive disorder • A disorder caused due to deficiency of phenylalanine hydroxylase • Frequency 1 in 20,000 • Blockage of conversion to tyrosine results in ~20 fold increase in Phe. • Concentration of phenylpyruvate increases resulting in excretion in urine • Addition of ferric chloride to urine turns it olive green • Phenylketonuric are severally mentally retarded, if not properly treated • Low Phe diet is solution to the problem Aminoacids

32. Classification of Polar Amino Acids Aminoacids

33. Charged Amino Acids Aminoacids

34. Polar aminoacids • Aminoacids containing hydroxyl group • May be post-transcriptionally phosphorylated • Ser/Thr and Tyr phophorylation are very important in • Cellular signaling • cell cycle regulation and tumor development Aminoacids

35. Serine • Precursor for the synthesis of cysteine, choline and cephalins • Takes part in the synthesis of nucleic acid bases • Can be converted into glycine and pyruvic acid • Serves as carrier of phosphorus in phosphoproteins Aminoacids

36. Threonine • Can be converted into glycine • Can be converted in propionyl-CoA and then to succinyl-CoA • Serves as carrier of phosphorus in phosphoproteins Aminoacids

37. Tyrosine • Obtained from phenylalanine • Can be converted to dihydroxyphenylalanine (DOPA) and Dopamine • Dopamine is precursor of catecholamines (adrenaline and nor-adrenaline) • Tyrosine is also a precursor for T3 and T4 • Skin pigment, melanin is also a produce to tyrosine metabolism Aminoacids

38. Basic Aminoacids • Aminoacid group of these aminoacids gets ionized in acidic pH range • They may make part of active site • Basic aminoacids include lysine, argenine and histidine Aminoacids

39. Lysine • It is a basic aminoacid • It is among essential aminoacids • It does not allow α-helix to be formed/continued Aminoacids

40. Argenine • Its hydrolysis yields urea • Takes part in urea cycle • Contributes in the formation of creatine • An essential aminoacid • Does not allow formation of α-helix Aminoacids

41. Histidine • Contains an imidazole ring • Near neutral pH the imidazole ring gets charged • It is often found in the active site of enzymes • Imidazole ring can act as electron acceptor/donor in an enzyme catalyzed reactions Aminoacids

42. Acidic aminoacids • These aminoacids contain an additional –COOH group • They get ionized in the basic pH range • Their side chains may act as proton acceptor • They may make part of active site of an enzyme • They may accept an amino group to become amides i.e. asparagine and glutamine • Glutamine play important role in nitrogen transport/urea cycle Aminoacids

43. Essential Aminoacids Aminoacids

44. Aminoacids in special sources • Non-protein aminoacids • May be a part of some molecules • Play important role in physiological functions Aminoacids

45. 1,2. Citruline and ornithine • Found in liver • Intermediates of urea cycle • Take part in conversion of NH3 to urea H2N-(CH2)3-CH-COOH C=O Ornithine Citrulline NH2 NH2 H-N-(CH2)3-CH-COOH NH2 Aminoacids

46. 3. β-alanine • Part of vitamin B (pantothenic acid) H2N-CH2-CH2-COOH Aminoacids

47. 4. Pantothenic acid • A widely distributed vitamin • Make a part of co-enzyme A (Co-A) • Take part in a large number of metabolic reactions CH2—C—CH—C—NH—CH2—CH2—COOH CH3 O OH CH3 OH Aminoacids

48. 5. γ-aminobutyric acid (GABA) • GABA is a neurotransmitter • Found in nervous tissue H2N-CH2-CH2-CH2-COOH Aminoacids

49. 6. Dihydroxyphenylalanine (DOPA) • A metabolite of phenylalanine and tyrosine • L-DOPA is used in treatment of Parkinsons Disease OH OH Aminoacids

50. 7. Homocystine • Formed by de-methylation of methionine H Aminoacids