Lelly Yuniarti, S.Si., M.Kes Amino Acid and Protein1

Learning Objective Amino Acid and Protein3 SPECIFIC LEARNING OBJECTIVE At the end of the session the student should be able to explain:  Structures of amino acids  Function of protein  Peptides and proteins  Classification of protein  Nature of Protein and Amino acid  Denaturation of protein

Chemical Elements of Living Matter Amino Acid and Protein4

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I.AMINO ACID Amino acids are fundamental units of proteins. Amino Acid and Protein6

continue d Amino Acid and Protein7

Essential Amino Acid Trivial NameSymbolTrivial NameSymbol Alanin Arginin Asparagin Asam aspartat Sistein Glutamin Asam glutamat Glisin Histidin isoleusin ala arg asn asp sis gln glu gli his ile (+) Lesina Lisina Metionin Fenilalanina Prolina Serina Treonina Triptofan Tirosina Valina les (+) lis (+) met (+) fen (+) pro ser tre (+) trp (+) tir val Amino Acid and Protein8

Structure of the α-Amino Acids All proteins are polymers, and the monomers combine are α-Amino Acids. A representative α-Amino Acids, e.g.. valine is shown in figure: Amino Acid and Protein9

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A. Composition  The amino group are attached to the  -carbon, the carbon next to the carboxyl group, hence the name  -amino acids.  To the  -carbon of every amino acid are also attached a hydrogen atom and side chains (R).  Their different side chains distinguish different  -amino acids.  We can write the general structure for an  - amino acid in next figure: Amino Acid and Protein11 H O R – C – C OH NH 2

 The complete structures of these amino acids are shown in next slide (slide no.9).  Only 20  -amino acids used by cells when they synthesize protein.  Hydroxyproline, present mainly in collagen, is synthesized from proline, and cystine, present in most proteins, is synthesized from cysteine. Amino Acid and Protein12

Figure 5.3: The amino acids found in proteins Amino Acid and Protein13 continued Below each amino acid are its name. Its three-letter abbreviation, and its one-letter abbreviation

Continued from Figure 5.3: The amino acids found in proteins Amino Acid and Protein14 continued

Amino Acid and Protein15 continued Continued from Figure 5.3: The amino acids found in proteins

Amino Acid and Protein16 Continued from Figure 5.3: The amino acids found in proteins

The taste map on the tongue Amino Acid and Protein17 Expire

B. Amphoteric properties  Amino acids are amphoteric molecules ; that is, they have both basic and acidic groups  Monoamino-monocarboxylic acids exist in solution neutral pH are predominantly dipolar ions (or zwitter ion). In dipolar form of an amino acid, the amino group is protonated and positively charged (-NH 3 + ) and the carboxyl group is dissociated and negatively charged (-COO - ) Amino Acid and Protein18 continued H O R – C – C O – NH 2 Cationic form charge +1 pH IEP Zwitter ion form charge 0 pH IEP Anionic form charge -1 pH IEP H O R – C – C OH NH 3 + H O R – C – C O – NH 3 + OH – H+H+ H+H+

 At low pH, the carboxyl group accepts a proton and becomes uncharged, so that the overall charge on the molecule is positive  At high pH, the amino group loses its proton and becomes uncharged; thus, the overall charge on the molecule is negative Amino Acid and Protein19

C. Stereochemistry of the α- amino acids  The  -carbon of amino acids are formed an asymmetric molecule, the  -carbon is said to be chiral or stereocenter or also called an asymmetric carbon.  The important fact that all of the amino acids incorporated by organisms into proteins are of the L-form, with the exception of glycine  D-isomers of amino acids exist in nature, and some play important biochemical roles but they are never found in proteins. Amino Acid and Protein20