amino acids for web

8/13/2019 Amino Acids for Web

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Chapter-3

Part-1

Amino acids

Amino acids,

peptides, andproteins


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There are only 20standard amino acids

or primary amino acidsor common amino acids

Amino acids are precursorsof proteins


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Biological catalyst

Functions of proteins

TransportStructural support

Immune responseBiological regulation


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Functions of Proteins

Biological catalyst Transport Structural support


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Functions of Proteins

Immune response Biological regulation


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Is it mathematically possibleto make thousands of proteins

from only 20 amino acids?

A Protein made up of only 8 aminoacids has a mathematical possibilities

of making 2.56 x 1010differentsequences

Most proteins are made up of 200-500amino acids


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General structure of an

amino acid


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Stereoisomerism in -Amino acids


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Almost all amino acids

found in proteins existin L-isomeric form

Exceptions!!

Certain bacterial peptides contain D-isomers of amino acids


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Classification of

amino acids

5: Negatively charged amino acids

1: Non-polar Amino acids

2: Polar uncharged amino acids

3: Aromatic amino acids

4: Positively charged amino acids


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Non-polar amino acids

1: Glycine

2: Alanine

3: Valine

4: Leucine

5: Isoleucine

6: Methionine

7: Proline


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Uncharged polaramino acids

1: Serine

2: Thereonine3: Cysteine

4: Asparagine

5: Glutamine


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Oxidation of two cysteine moleculesform disulfide bond

Oxidation

Reduction

Reversible reaction


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Two types ofdisulfide bonds

Intra-molecular

disulfide bond

Inter-moleculardisulfide bond

Insulin molecule


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Aromatic amino acids

2: Tyrosine

1: Phenylalanine

3: Tryptophan


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Structure and solubility

Which ismore

soluble?


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Positively chargedamino acids

1: Lysine

2: Arginine

3: Histidine


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?


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2: Glutamate

Negatively chargedamino acids

1: Aspartate


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N t d d


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Non-standardamino acids

Ornithine

4-Hydroxyproline

Citrulline

5-Hydroxylysine

N-Methyllysine

N t d d i id


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Non-standard amino acids


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Non-standard amino acids


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Amino acid abbreviationsandsymbols

For convenience, the names of all thestandard amino acids are designated by

eitherthree letter abbreviations or by oneletter symbol

F i id h fi


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Ile - Isoleucine

Formost amino acids, the firstthree letters of their namesrepresent the abbreviations

Exceptions !!

Asn - Asparagine

Gln - Glutamine

Trp - Tryptophan


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Amino acids can act asacids and bases

Amino acid as base (proton acceptor)


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Amino acid acts as diprotic acid

+1 0 -1

H h h i id


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pH changes charge on amino acids


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Titration curveof glycine


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Amino acids with non-ionizable Rgroups have titration curve similar to

that of glycine and also have similarpK1and pK2values

pK1refer to pKaof COOH groups andranges from 1.8-2.4

pK2refer to pKaof NH3+groups and

ranges from 8.8-11.0


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Isoelectricpoint (pI)

pI is the pH atwhich a

molecule carriesNO net charge


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Titration curve of glutamate


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Titration curve of glutamate

pI of negatively chargedamino acids is the average

of pK1and pKR

1/2 (2.19 + 4.25) = 3.22

Titration curve of histidine


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Titration curve of histidine

pI of positively chargedamino acids is the average

of pK2and pKR

1/2 (9.17 + 6.0) = 7.59

At h t H ill hi tidi d l


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?

At what pH will histidine develop apositive charge?

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