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CHMI 2227EBiochemistry I

Amino acids:-Structure-General chemical properties

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Proteins: Building blocks of life!

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Amino acids

CHR

COOH

NH2

C

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General properties of amino acids.

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General properties of amino acids.

Zwitterion

Net charge: +1 Net charge: 0 Net charge: -1

Acidic pH Basic pHpKa 1(pH 2-2.5)

pKa 2(pH 9-10.5)

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Amino acid titration1. simplest scenario

Buffer!

Buffer!

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The twenty amino acids:

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Structure of the 20 amino acids1. Hydrophobic amino acids

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Structure of the 20 amino acids1. Hydrophobic amino acids

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Structure of the 20 amino acids2. Aromatic amino acids

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Structure of the 20 amino acids2. Aromatic amino acids

Absorbance max

(nm)

MolarAbsorbance(M-1 cm-1)

Phenylalanine 257.4 197

Tyrosine 274.6 1420

Tryptophan 279.8 5690

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Structure of the 20 amino acids3. polar, uncharged amino acids

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Structure of the 20 amino acidsCysteine and cystine

Disulfide bond

In biochem:-oxidation: lose H-Reduction: gain H

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Structure of the 20 amino acids Tyr, Ser, Thr

P=O

O-

O-

Ser

Phospho-Ser

Proteinkinase

Proteinphosphatase

ATP

ADP H2O

PO4-3

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Structure of the 20 amino acids4. Negatively charged amino acids

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Structure of the 20 amino acids4. Negatively charged amino acids

pKa1 pKa2pKaR

What is the pI of glutamate?

NaOH

pH

pKa1

pKaR

pKa29.5

4.1

2.1

100% A

100% B

100% C

100% D

A B C D

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Structure of the 20 amino acids5. Positively charged amino acids

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Structure of the 20 amino acids5. Positively charged amino acids: His

pKaR

pKa2

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Structure of the 20 amino acidspKa values of amino acids

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Analysis of amino acids1. Ion exchange chromatography

Elution

+ +

pH >> pI pH << pI

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Analysis of amino acids2. Detection of amino acids: ninhydrin reagent

O

O

OHOH

Ninhydrin Amino acid

2

O

O

N

O

O

CH

R

COO-

NH3+

CO2

Purple!!

R-HC=O