AMINO ACID AND PROTEIN

Lelly Yuniarti, S.Si., M.Kes

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Learning Objective

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SPECIFIC LEARNING OBJECTIVEAt the end of the session the student should be able to explain:Structures of amino acids Function of proteinPeptides and proteinsClassification of proteinNature of Protein and Amino acidDenaturation of protein

Chemical Elements of Living Matter

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I .AMINO ACIDAmino acids are fundamental units of proteins.

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continued

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Essential Amino Acid

Trivial Name Symbol Trivial Name Symbol

AlaninArginin

AsparaginAsam aspartat

SisteinGlutamin

Asam glutamatGlisin

Histidinisoleusin

alaargasnaspsisglngluglihis

ile (+)

LesinaLisina

MetioninFenilalanina

ProlinaSerina

TreoninaTriptofanTirosinaValina

les (+)lis (+)

met (+)fen (+)

proser

tre (+)trp (+)

tirval

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Structure of the α-Amino AcidsAll proteins are polymers, and the

monomers combine are α-Amino Acids.A representative α-Amino Acids, e.g..

valine is shown in figure:

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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:

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H

OR – C – C

OH NH2

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 Protein 12

Figure 5.3: The amino acids found in proteins

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Below each aminoacid are its name. Its three-letterabbreviation, andits one-letterabbreviation

Continued from Figure 5.3: The amino acids found in proteins

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Continued from Figure 5.3: The amino acids found in proteins

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Continued from Figure 5.3: The amino acids found in proteins

The taste map on the tongue

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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 (-NH3

+) and the carboxyl group is dissociated and negatively charged (-COO-)

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H

OR – C – C

O–

NH2

Cationic form charge +1 pH IEP

Zwitter ion form charge 0 pH IEP

Anionic form charge -1 pH IEP

H

OR – C – C

OH NH3

+

H

OR – C – C

O–

NH3+

OH–

H+

OH–

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

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C. Stereochemistry of the α-amino acidsThe -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.

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