1 / 94

WEEK-1 Amino Acids PROF. SBW

WEEK-1 Amino Acids PROF. SBW. BLOG: www.simonbw.lecture.ub.ac.id Page/HALAMAN: KULIAH S-1 dibawah : KIMIA PANGAN BARU SEM 2012/2013 PASSWORD: cucu1. BAGI MHSW BARU SEM 2 TERLAMBAT > 5 MENIT, JANGAN MASUK, KARENA SDR AKAN DIUSIR DARI RUANGAN. KERJAKAN LATIHAN DIBLOG, AGAR MUDAH LULUSNYA.

yukio
Télécharger la présentation

WEEK-1 Amino Acids PROF. SBW

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. WEEK-1 Amino AcidsPROF. SBW

  2. BLOG: www.simonbw.lecture.ub.ac.id • Page/HALAMAN: KULIAH S-1 dibawah: KIMIA PANGAN BARU SEM 2012/2013 • PASSWORD: cucu1

  3. BAGI MHSW BARU SEM 2 • TERLAMBAT > 5 MENIT, JANGAN MASUK, KARENA SDR AKAN DIUSIR DARI RUANGAN. • KERJAKAN LATIHAN DIBLOG, AGAR MUDAH LULUSNYA. • QUIS 15-20 MENIT SETELAH KULIAH KE-3

  4. Topics Covered: Amino Acids - Classification & Physical Properties Stereochemistry of a-Amino Acids Common a-Amino Acids: Review of Structure Effect of pH on the Structure of a-Amino Acids 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. a-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 (—NH2) and a carboxylic acid (-CO2H), these groups are actually present as their conjugate acid (—NH3+) and conjugate base (—CO2–), 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. +H3N-CH2CO2- 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. 27.2Stereochemistry of a-Amino Acids

  16. Chirality, Chiral & Stereogenic Centers Chirality the term describing an object that is not superimposable on its mirror image 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

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

  18. With the Exception of Glycine, a-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 a-Amino Acids in Nature Most of the a-amino acids in proteins have the L-configuration at their carbon

  20. Configuration of a-Amino Acids in Nature

  21. Occurrence of a-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 27.1. tolong cari sendiri.

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

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

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

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

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

  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 Proline (Pro, P) 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.

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

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

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

  35. Polar, Non-Ionized Side Chains: Serine Serine (Ser, S) The hydroxymethyl (-CH2OH) side chain in serine can be involved in hydrogen bonding and can behave as a nucleophile.

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

  37. Polar, Non-Ionized Side Chains: Cysteine Cysteine (Cys, C) 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.

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

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

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

  41. Essential a-Amino Acids can be Subdivided According to the Nature of Side Chain • General categories of a-amino acids • Non-polar side chains • Polar but non-ionized side chains • Brønsted acidic side chains • 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 a-Amino Acids can be Subdivided According to the Nature of Side Chain • General categories of a-amino acids • Non-polar side chains • Polar but non-ionized side chains • Brønsted acidic side chains • 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 Guanidinium Ion Guanidine is a significantly stronger base thantriethylamine Triethylamine

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

  50. Protonation of Histidine

More Related