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WEEK-1 Amino Acids PROF. SBW. BLOG: www.simonbw.lecture.ub.ac.idBLOG: www.simonbw.lecture.ub.ac.id www.simonbw.lecture.ub.ac.id Page/HALAMAN: KULIAH S-1.

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Presentasi berjudul: "WEEK-1 Amino Acids PROF. SBW. BLOG: www.simonbw.lecture.ub.ac.idBLOG: www.simonbw.lecture.ub.ac.id www.simonbw.lecture.ub.ac.id Page/HALAMAN: KULIAH S-1."— Transcript presentasi:

1 WEEK-1 Amino Acids PROF. SBW

2 BLOG: Page/HALAMAN: KULIAH S-1 dibawah: KIMIA PANGAN BARU SEM 2012/2013Page/HALAMAN: KULIAH S-1 dibawah: KIMIA PANGAN BARU SEM 2012/2013 PASSWORD: cucu1PASSWORD: cucu1

3 BAGI MHSW BARU SEM 2BAGI MHSW BARU SEM 2 TERLAMBAT > 5 MENIT, JANGAN MASUK, KARENA SDR AKAN DIUSIR DARI RUANGAN.TERLAMBAT > 5 MENIT, JANGAN MASUK, KARENA SDR AKAN DIUSIR DARI RUANGAN. KERJAKAN LATIHAN DIBLOG, AGAR MUDAH LULUSNYA.KERJAKAN LATIHAN DIBLOG, AGAR MUDAH LULUSNYA. QUIS MENIT SETELAH KULIAH KE-3QUIS MENIT SETELAH KULIAH KE-3

4 Topics Covered: 1. 1.Amino Acids - Classification & Physical Properties 2. 2.Stereochemistry of  Amino Acids 3. 3.Common  Amino Acids: Review of Structure 4. 4.Effect of pH on the Structure of  Amino Acids 5. 5.Isoelectric Point of Amino Acids Today’s Lecture

5 27.1 Classification of Amino Acids

6 Classification of Amino Acids amino acids are classified as , etc. to indicate where the nitrogen atom is relative to the carboxylic acid:

7  Amino Acids are Most Ubiquitous in Nature

8 Revision: Amines are Brønsted Bases Amines are electron-rich and have a reactive lone pair, which can form a covalent bond to a proton to form an ammonium ion.

9 Amino Acids Exist as Zwitterions While their name implies that amino acids are compounds that contain an amine (— NH 2 ) and a carboxylic acid (-CO 2 H), these groups are actually present as their conjugate acid (—NH 3 + ) and conjugate base (—CO 2 – ), respectively.

10 Amino Acids Exist as Zwitterions Resonance-Stabilized Zwitterion

11 Zwitterions Defined Zwitterionic Compounds/Zwitterions neutral compounds having formal unit electrical charges of opposite sign. Some chemists restrict the term to compounds with the charges on non- adjacent atoms. Sometimes referred to as inner salts, dipolar ions (a misnomer), e.g. + H 3 N-CH 2 CO 2 - ammonioacetate (glycine). IUPAC Compendium of Chemical Terminology

12 Amino Acids Exist as Zwitterions What evidence do we have for this behavior………

13 Properties of Glycine Reflect its Zwitterionic Structure High Water Solubility glycine is soluble in water but not in non- polar solvents. High Melting Point when heated to 233°C it decomposes before it melts.

14 Properties of Glycine Reflect its Zwitterionic Structure The physical properties of glycine are consistent with this structure

15 27.2 Stereochemistry of  -Amino Acids

16 Chirality, Chiral & Stereogenic Centers Chiral Center an atom that has four nonequivalent atoms or groups attached to it. At various times, chiral centers have been and are called asymmetric centers or stereogenic centers Chirality the term describing an object that is not superimposable on its mirror image

17 Fisher Projections and the D/L Stereochemical Convention Fisher Projection

18 With the Exception of Glycine,  -Amino Acids are Chiral Molecules Glycine has no stereogenic center and is therefore achiral All Other A.A.s have a stereogenic center and are therefore chiral Non- superimposable isomers (enantiomers)

19 Configuration of  -Amino Acids in Nature Most of the  -amino acids in proteins have the L -configuration at their   carbon

20 Configuration of  -Amino Acids in Nature

21 Occurrence of  -Amino Acids in Nature More than 700 amino acids occur naturally, but 20 of them are especially important. These 20 amino acids are the building blocks of proteins. All are  -amino acids. They differ in respect to the group attached to the  carbon. These 20 are listed in Table tolong cari sendiri.

22 The Nature of  -Side Chain Determines the Physical Properties of Amino Acids The major differences among the side chains concern: Size and shape Electronic characteristics

23 Essential  -Amino Acids can be Subdivided According to the Nature of Side Chain General categories of  -amino acids 1.Non-polar side chains 2.Polar but non-ionized side chains 3.Brønsted acidic side chains 4.Brønsted basic side chains

24 Essential  -Amino Acids can be Subdivided According to the Nature of Side Chain General categories of  -amino acids 1.Non-polar side chains 2.Polar but non-ionized side chains 3.Brønsted acidic side chains 4.Brønsted basic side chains

25 Non-Polar Side Chains: Glycine Glycine is the simplest amino acid and is achiral Glycine (Gly, G)

26 Non-Polar Side Chains: Alanine Alanine, valine, leucine, and isoleucine have alkyl groups as side chains, which are non-polar and hydrophobic Alanine (Ala, A)

27 Non-Polar Side Chains: Valine Valine (Val, V)

28 Non-Polar Side Chains: Leucine Leucine (Leu, L)

29 Non-Polar Side Chains: Isoleucine Isoleucine (Ile, I)

30 Non-Polar Side Chains: Methionine Methionine (Met, M) the side chain in methionine is non-polar, but the presence of sulfur makes it somewhat polarizable.

31 Non-Polar Side Chains: Proline Among the 20 essential amino acids, proline is the only amino acid that contains a secondary amine function. Its side chain is non-polar and cyclic. Proline (Pro, P)

32 Non-Polar Side Chains: Phenylalanine The side chain in phenylalanine (a non- polar amino acid) is a benzyl group. Phenylalanine (Phe, F)

33 Non-Polar Side Chains: Tryptophan The side chain in tryptophan (a non-polar amino acid) is larger and more polarizable than the benzyl group of phenylalanine. Tryptophan (Trp, W)

34 Essential  -Amino Acids can be Subdivided According to the Nature of Side Chain General categories of  -amino acids 1.Non-polar side chains 2.Polar but non-ionized side chains 3.Brønsted acidic side chains 4.Brønsted basic side chains

35 Polar, Non-Ionized Side Chains: Serine The hydroxymethyl (-CH 2 OH) side chain in serine can be involved in hydrogen bonding and can behave as a nucleophile. Serine (Ser, S)

36 Polar, Non-Ionized Side Chains: Threonine The side chain in threonine can be involved in hydrogen bonding, but is somewhat more crowded than in serine Threonine (Thr, T)

37 Polar, Non-Ionized Side Chains: Cysteine Cysteine is a thiol. In proteins, the side chains of two remote cysteine residues can be joined, via oxidation, to form a S-S bond, or disulfide bridge. Cysteine (Cys, C)

38 Polar, Non-Ionized Side Chains: Tyrosine The side chain of tyrosine is similar to that of phenylalanine but can participate in hydrogen bonding Tyrosine (Tyr, Y)

39 Polar, Non-Ionized Side Chains: Asparagine The side chains of asparagine and glutamine (next slide) terminate in amide functions that are polar and can engage in hydrogen bonding. Asparagine (Asn, N)

40 Polar, Non-Ionized Side Chains: Glutamine Glutamine (Gln, Q)

41 Essential  -Amino Acids can be Subdivided According to the Nature of Side Chain General categories of  -amino acids 1.Non-polar side chains 2.Polar but non-ionized side chains 3.Brønsted acidic side chains 4.Brønsted basic side chains

42 Brønsted Acidic Side Chains: Aspartic Acid Aspartic Acid (Asp, A) Aspartic acid and glutamic acid (next slide) exist as their conjugate bases at biological pH. They are negatively charged and can form ionic bonds with positively charged species.

43 Brønsted Acidic Side Chains: Glutamic Acid Glutamic Acid (Glu, U)

44 Essential  -Amino Acids can be Subdivided According to the Nature of Side Chain General categories of  -amino acids 1.Non-polar side chains 2.Polar but non-ionized side chains 3.Brønsted acidic side chains 4.Brønsted basic side chains

45 Brønsted Basic Side Chains: Lysine Lysine (Lys, K) Lysine and arginine (next slide) exist as their conjugate acids at biological pH. They are positively charged and can form electrostatic interactions with negatively charged species

46 Brønsted Basic Side Chains: Arginine Arginine (Arg, G) Arginine is a derivative of lysine: it contains a basic guanidine group.

47 New Functional Group: Guanidine Guanidine Guanidine is a significantly stronger base thantriethylamin e Triethylamine Guanidinium Ion

48 Brønsted Basic Side Chains: Histidine Histidine (His, H) Histidine is a basic amino acid, but less basic than lysine and arginine. Histidine can interact with metal ions and can help move protons from one site to another.

49 q. Which nitrogen atom is protonated in the imidazole ring of histidine? Protonation of Imidazole a. This one 

50 Protonation of Histidine

51 27.3 Acid-Base Behavior of Amino Acids

52 Effects of pH on Structure of Glycine At low pH, that is in strongly acidic solution, glycine is protonated and exists as a monocation.

53 What Happens when pH of Solution Increases? As the pH of solution increases, the concentration of hydroxide ions also increases. At a give point, the most acidic group in the ion shown below will be deprotonated. Typical ammonium ion: pK a ~9 Typical carboxylic acid: pK a ~5

54 As the pH of solution increases the carboxylic acid is deprotonated to form a neutral zwitterion. The pKa of glycine is This is lower than acetic acid (4.76) because of the presence of the electron withdrawing ammonium substituent. Glycine is a Stronger Acid than Acetic Acid

55 Isoelectric Point Isoelectric point The pH value at which the net electric charge of an elementary entity is zero. pI is a commonly used symbol for this kind-of- quantity. It should be replaced by pH(I) because it is a pH determined under that particular condition.

56 Zwitterionic structure is neutral and its value of pH is called isoelectric point.Zwitterionic structure is neutral and its value of pH is called isoelectric point.

57 Nilai pKa dan pI dari gugus asam amino bebas dan 25 0C

58 Kurva titrasi asam amino dengan basa (NaOH) dan Asam (HCL)

59 REAKSI GUGUS ASAM DAN BASA DARI ASAM AMINO BILA DITITRASI ZWITTER ION ATAU SALING MENETRALKAN

60 Calculation of Isoelectric Point The pH(I) is the numerical average of the pK a values for the carboxylic acid and the ammonium group /2 = 5.97 The pH(I) of glycine is 5.97

61 As the pH of solution increases above the isoelectric point, a proton is removed from the ammonium group (pKa = 9.3) of the zwitterion to generate the anionic form of the amino acid. What Happens when pH of Solution Rises Above pH(I)?

62 The Overall Charge of Amino Acids Changes as a Function of pH Increasing pH

63 Isoelectric Points of Essential  -Amino Acids General categories of  -amino acids 1.Amino acids with neutral side chains 2.Amino acids with ionizable side chains

64 Neutral Side Chains: Glycine Glycine (Gly, G) pK a1 = 2.34 pK a2 =9.60 pH(I) =5.97

65 Neutral Side Chains: Alanine Alanine (Ala, A) pK a1 = 2.34 pK a2 =9.69 pH(I) =6.00

66 Neutral Side Chains: Valine Valine (Val, V) pK a1 = 2.32 pK a2 =9.62 pH(I) =5.96

67 Neutral Side Chains: Leucine Leucine (Leu, L) pK a1 = 2.36 pK a2 =9.60 pH(I) =5.98

68 Neutral Side Chains: Isoleucine Isoleucine (Ile, I) pK a1 = 2.36 pK a2 =9.60 pH(I) =5.98

69 Neutral Side Chains: Methionine Methionine (Met, M) pK a1 = 2.28 pK a2 =9.21 pH(I) =5.74

70 Neutral Side Chains: Proline Proline (Pro, P) pK a1 = 1.99 pK a2 =10.60 pH(I) =6.30

71 Neutral Side Chains: Phenylalanine Phenylalanine (Phe, F) pK a1 = 1.83 pK a2 =9.13 pH(I) =5.48

72 Neutral Side Chains: Tryptophan Tryptophan (Trp, W) pK a1 = 2.83 pK a2 =9.39 pH(I) =5.89

73 Neutral Side Chains: Serine Serine (Ser, S) pK a1 = 2.02 pK a2 =8.80 pH(I) =5.41

74 Neutral Side Chains: Threonine Threonine (Thr, T) pK a1 = 2.09 pK a2 =9.10 pH(I) =5.60

75 Neutral Side Chains: Cysteine Cysteine (Cys, C) pK a1 = 1.96 pK a2 =8.18 pH(I) =5.07

76 Neutral Side Chains: Tyrosine Tyrosine (Tyr, Y) pK a1 = 2.20 pK a2 =9.11 pH(I) =5.66

77 Neutral Side Chains: Asparagine Asparagine (Asn, N) pK a1 = 2.02 pK a2 =8.80 pH(I) =5.41

78 Neutral Side Chains: Glutamine Glutamine (Gln, Q) pK a1 = 2.17 pK a2 =9.13 pH(I) =5.65

79 Isoelectric Points of Essential  -Amino Acids General categories of  -amino acids 1.Amino acids with neutral side chains 2.Amino acids with ionizable side chains

80 Amino Acids with Acidic Side Chains have Three pKa Values to Consider pH(I) is between 1.88 and 3.65

81 Calculation of pH(I) for Amino Acids with Acidic Side Chains For amino acids with acidic side chains, pH(I) is the average of pK a1 and pK a /2 = 2.77 The pH(I) of aspartic acid is 2.77

82 Ionizable Side Chains: Aspartic Acid Aspartic Acid (Asp, A) pK a1 = 1.88 pK a2 =3.65 pK a3 =9.60 pH(I) =2.77

83 Ionizable Side Chains: Glutamic Acid Glutamic Acid (Glu, U) pK a1 = 2.19 pK a2 =4.25 pK a3 =9.67 pH(I) =3.22

84 Amino Acids with Ionizable Side Chains have Three pKa Values to Consider pH(I) is between 8.95 and 10.53

85 Calculation of pH(I) for Amino Acids with Basic Side Chains For amino acids with basic side chains, pH(I) is the average of pK a2 and pK a /2 = 9.74 The pH(I) of lysine is 9.74

86 Ionizable Side Chains: Lysine Lysine (Lys, K) For amino acids with basic side chains, pH(I) is the average of pK a2 and pK a3. pK a1 = 2.18 pK a2 =8.95 pK a3 =10.53 pH(I) =9.74

87 Ionizable Side Chains: Arginine Arginine (Arg, G) pK a1 = 2.17 pK a2 =9.04 pK a3 =12.48 pH(I) =10.76

88 Ionizable Side Chains: Histidine Histidine (His, H) pK a1 = 1.82 pK a2 =6.00 pK a3 =9.17 pH(I) =7.59

89 Properties of Amino-Acids Because they are zwitterions at neutral pH, amino acids have many of the physical properties we associate with salts:Because they are zwitterions at neutral pH, amino acids have many of the physical properties we associate with salts: –can form crystals –have high melting points –are soluble in water –not soluble in hydrocarbon solvents 89

90 REAKSI GUGUS ASAM AMINO REAKSI DENGAN REAGEN NINHYDRINREAKSI DENGAN REAGEN NINHYDRIN Reaksi ini digunakan untuk analisa/mendeteksi adanya asam amino bebas dari suatu bahan:Reaksi ini digunakan untuk analisa/mendeteksi adanya asam amino bebas dari suatu bahan: Diukur dengan 570 nm, warna ungu, krn adanya seny. Hydrindantin + CO2+H2O+ aldehideDiukur dengan 570 nm, warna ungu, krn adanya seny. Hydrindantin + CO2+H2O+ aldehide

91 REAKSI DENGAN REAGEN FLUORESCAMINE DIGUNAKAN UNTUK MENDETEKSI ASAM-2 AMINO, PEPTIDA DAN PROTEIN yang mengandung gugus amine primer, diukur dengan 470 nm, warnanya fluorescence tajam.DIGUNAKAN UNTUK MENDETEKSI ASAM-2 AMINO, PEPTIDA DAN PROTEIN yang mengandung gugus amine primer, diukur dengan 470 nm, warnanya fluorescence tajam.

92 REAKSI KIMIA GUGUS ASAM AMINO SECARA KIMIA LIHAT E-BOOK: FOOD CHEMISTRY OLEH FENNEMA di BLOG SBWLIHAT E-BOOK: FOOD CHEMISTRY OLEH FENNEMA di BLOG SBW JUDUL: FOOD CHEMISTRY, 3 rd EDITION, FENNEMA, MARCEL DEKKER PUB.JUDUL: FOOD CHEMISTRY, 3 rd EDITION, FENNEMA, MARCEL DEKKER PUB.

93 SIFAT FISIKO-KIMIA ASAM AMINO YANG LAIN SIFAT HIDROFOBISITAS: REAKSI KELARUTAN ASAM AMINO DALAM AIR DAN ETANOL (LIHAT DETAIL DI E-BOOK)SIFAT HIDROFOBISITAS: REAKSI KELARUTAN ASAM AMINO DALAM AIR DAN ETANOL (LIHAT DETAIL DI E-BOOK) ARTINYA MANA-2 JENIS ASAM AMINO YG LARUT DALAM AIR DAN LARUT DALAM ETANOL. ARGININE, VALINE, LYSINE, ALANINE LARUT DALAM AIR.ARTINYA MANA-2 JENIS ASAM AMINO YG LARUT DALAM AIR DAN LARUT DALAM ETANOL. ARGININE, VALINE, LYSINE, ALANINE LARUT DALAM AIR. SIFAT OPTIK: TRP, TYR DAN Phe Mengobsorpsi sinar pada ג nm dan Tyr dan Trp berfluorescene pada lingkungan polaritas medium larutan.SIFAT OPTIK: TRP, TYR DAN Phe Mengobsorpsi sinar pada ג nm dan Tyr dan Trp berfluorescene pada lingkungan polaritas medium larutan.

94 Latihan AA APA YANG DIMAKSUD DGN pI, kapan terjadinyaAPA YANG DIMAKSUD DGN pI, kapan terjadinya Jelaskan klasifikasi AA dan beri contohJelaskan klasifikasi AA dan beri contoh Bagaimana proses protonasi dan deprotonasi asam amino dapat terjadiBagaimana proses protonasi dan deprotonasi asam amino dapat terjadi Apakah beda produk pangan nabati dan hewani ditinjau dari jenis dan jumlah asam amino yang ada dalam ke dua produk pangan tsb.Apakah beda produk pangan nabati dan hewani ditinjau dari jenis dan jumlah asam amino yang ada dalam ke dua produk pangan tsb.


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