Proteins

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Proteins
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• Polymers of amino acids
• O O
• -(NH-CH C-)-(NH-CH-C-)-
• G G
• N-terminal C-terminal

3
Amino Acids

• 20 natural a-amino carboxylic acids
• 19 are primary amines, proline is 2 amine
• 19 are chiral, glycine is not

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Classification of Amino Acids

• Non Polar (example alkanes)
• Polar
• Neutral (example alcohols)
• Acidic (example carboxylic acids)
• Basic (example amines)
• You will have the table from the book.

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pH Effect on Amino Acids

• Amino acid in acidic solution
• Amino acid in basic solution

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Zwitterions

• When pH is equal to the pI (isoelectric point)
  amino acids exist in the zwitterion form.
• pH gt pI
• pH lt pI
• pH pI

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Example Sour milk

• Casein pI 4.7
• pH lowered using vinegar

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Protein Structure

• Primary structure
• Order of amino acids in chain

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• Secondary structure interactions between
  backbone molecules of polypeptide chain.
• a-helix
• ß-pleated sheet
• random coil

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• Tertiary structure interactions between the
  side groups of the same chain.
• Disulfide bridges (-SS-)
• Hydrogen bonding
• Salt bridges
• Hydrophobic regions (nonpolar)
• Hydrophilic regions (polar)

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• Quaternary structure interactions between the
  side groups of different chains.
• Disulfide bridges (-SS-)
• Hydrogen bonding
• Salt bridges
• Hydrophobic regions (nonpolar)
• Hydrophilic regions (polar)

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Reactions

• Hydrolysis amide bonds are broken destroying
  the primary structure.
• (digestion)

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• Denaturation the protein is inactivated
• heat
• agitation
• microwaves
• UV light
• acids and bases
• alcohol