1. Dr.Md.Nazrul Islam Associate Professor of Biochemistry Dinajpur Medical College Bangladesh

2.  High molecular weight(5000-8000) polypeptide made up of L-amino acids linked by peptide bond or  High molecular weight polymers of L-AA linked by peptide bonds

3. Amino acid is a monomer of protein

4.  Amino acids are the amino (NH2) group containing carboxylic acid or  Monomer of protein containing both amino group and carboxyl group.  Weak organic acid

5. Chemical structure of amino acid Both groups are attached to same carbon atom(α) Besides these two groups also contains a distinct side chain R, so amino acid has a central asymmetric carbon atom to which following four different groups attached. NH2,COOH, H and R side chain The side group(R) creates unique characteristics for each amino acid so they differ in: shape, size, composition, electrical charge, and pH

6. NH2 group: Isoelectric pH is 9.0;so at body pH(7.4) it exist as protonated form(NH3+) Carboxyl group(COOH): Its isoelectric pH is 2.0; so at body pH(7.4) it exist as deprotonated form(COO-) R- side chain determines the properties and function of protein Hydrogen atom(H) Chemical structure of amino acid

12. Total 20 different amino acids in human body and all body proteins are constructed from these 20 amino acid and have specific genetic code, so they are called primary /standard amino acid Amino acids participation in protein synthesis are L-α type because NH2 group oriented on left side of α- carbon All amino acids except glycine have at least one asymmetrical carbon atom and show optical isomerism and optically active. General Introduction

13. Glycine have no R side chain(H at that place), no α asymmetric carbon atom and optically inac tive Amino acids are abbreviated by Ist three letter.ex-serine(ser) except tryptophan (Trp), Glutamine (Gln) and asparagine(Asn) General Introduction

16.  One amino acid join to the next by a PEPTIDE bond It is the covalent bond formed by joining the –COOH group of one amino acid and –NH2 group of another amino acid with removal of one molecule of water Between C and N Peptide Bond

17. Peptide bondCharacteristics: Covalent bond with partial double bond character Rigid, planar and do not rotate Not broken by denaturing agents Broken by proteolytic enzyme

21. Based on Number of peptide bond and number of amino acid

22. Peptide: 2-10 amino acid Polypeptide:10-100 amino acid Protein : >1oo amino acid

23. Based on different characteristics

24. Classification

25. A. Chemical classification 1  A.Monobasic and dibasic amino acids (Monoamino mono carboxylic acid and diamino dicarboxylic acid)-Neutral amino acid  B.Monoamino dicarboxylic acid-Acidic amino acid  C.Diamino mono carboxylic acid-Basic amino acid

26. 6.Aromatic amino acid- Phenylalanine.Tryptophan,Tyr osin

27. Mono amino mono carboxylic acid Mono basic-Neutral

29. Di basic-Neutral

30. B. Having more COOH group & less amino group

31. C. Having more amino group and less COOH group

33. 2

34. 2

35. B. Classification according to the polarity of side chain- R

37. NonPolar

38. Polar with no charge

39. Polar with charge

40. C. Nutritional classification

42. D. Metabolic classification

43.  Physical Properties  Chemical Properties

44. Physical Properties  Colorless  Crystalline  May be sweet (Glycine, Alanine, Valine), tasteless(Leucine) or bitter(Arginine, Isoleucine). Aspartame- An artificial sweetener contains Aspartic acid and Phenyl alanine.  Soluble in water, acids, alkalis but insoluble in organic solvents  High melting point(More than 200 0 c  Produce stereoisomer and having optical activity

45. Optical activity  The α carbon of each amino acid is attached to four different groups and is thus a asymmetric or chiral and optically active carbon atom.  Glycine is exceptional because there are two hydrogen substituents at the α carbon, thus it is optically inactive.  Amino acids with asymmetric centre at the α carbon can exist in two forms, D and L forms that are mirror images of each other and are called Enantiomers.  All amino acids found in proteins are of L- configuration  D- amino acids are found in some antibiotics and in bacterial cell walls.

47. Chemical Properties A. Isoelectric point  Amino acids can exist as ampholytes or zwitterions in solution, depending upon pH of the medium.  The pH at which the amino acids exist as zwitterions, with no net charge on them is called Isoelectric pH or Isoelectric point.  In acidic medium, the amino acids exist as cations  In alkaline medium, they exist as anions.

50. Cont…. B.Chemical reaction B.Chemical reaction: 1) Reactions due to amino group 2) Reactions due to carboxyl group 3) Reactions due to side chain 4) Reaction due to both amino and carboxyl groups

51. Reaction due to amino group  Oxidative deamination-α amino group is removed and corresponding α-keto acid is formed. α-keto acid produced is either converted to glucose or ketone bodies or is completely oxidized.  Transamination-Transfer of an α amino group from an amino acid to an α keto acid to form a new amino acid and a corresponding keto acid.  Formation of carbamino compound  CO2 binds to α amino acid on the globin chain of hemoglobin to form carbamino hemoglobin  The reaction takes place at alkaline pH and serves as a mechanism for the transfer of Carbon dioxide from the tissues to the lungs by

52. Reaction due to carboxylic group 1) Decarboxylation- Amino acids undergo alpha decarboxylation to form corresponding amines. Examples- Glutamic acid GABA Histidine Histamine Tyrosine Tyramine 2) Formation of amide linkage Non α carboxyl group of an acidic amino acid reacts with ammonia by condensation reaction to form corresponding amides Aspartic acid Asparagine Glutamic acidGlutamine

53. Reaction due to side chain 1)Ester formation  OH containing amino acids e.g. serine, threonine can form esters with phosphoric acid in the formation of phosphoproteins.  OH group containing amino acid can also form: Glycosides – by forming  O- glycosidic bond with carbohydrate residues.

54. Reaction due to side chain 2)Reactions due to SH group (Formation of disulphide bonds)  Cysteine has a sulfhydryl group( SH) group and can form a disulphide (S-S) bond with another cysteine residue.  The dimer is called Cystine  Two cysteine residues can connect two polypeptide chains by the formation of interchain disulphide chains

56. Reaction due to side chain3)Transmethylation The methyl group of Methionine can be transferred after activation to an acceptor for the formation of important biological compounds.

57. Reaction due to side chain 4.Reaction due to both amino and carboxylic group Formation of peptide bond.

58. Biological importance Building block of peptide and protein Support gluconeogenesis during starvation Transmission of nerve impulse(Gly, Glut) Precursor of hormone, purines, pyrimidines, vitamins,neurotransmitter and folate Detoxifixation Transport defect-amino acidouria Genetic defect in metabolism-Phenyl ketonuria, maple syrup urine disease. Sources of methyl and sulphar group Metabolic fluel for energy

59. Special functions of Amino acids  Incorporated in to tissue proteins  Niacin, Serotonin and melatonin are synthesized from Tryptophan  Melanin, thyroid hormone, catecholamines are synthesized from Tyrosine  GABA (neurotransmitter) is synthesized from Glutamic acid  Nitric oxide, a smooth muscle relaxant is synthesized from Arginine.  Act as precursors for haem, creatine and glutathione, Porphyrins, purines and pyrimidines

60. Amino acid derivatives Methionine : is methyl group donor Tryptophan: gives rise nicotinic acid, 5HT,Serotinine,melatonine,Pellegrahartnaps disease-absorbtion and transport defect. Glycine: Synthesis of Heme, purine, c- reactive,bile acid, component of collagen, detoxification of benzoic acid Phenylalanine: Catecolamine- Epineeprine, Nonepineprine, Dopamine Thyroid hormone and melanin, Phenylketonuria.

61. Amino acid sequence Dipeptide – 2 amino acids Tripeptide – 3 amino acids Oligopeptides – 4-10 amino acids Polypeptide – more than 10 amino acids Proteins in the body and diet are long polypeptides ( >100s of amino acids) Proteins in the body and diet are long polypeptides ( >100s of amino acids)