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Amino acids peptides and proteins

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    Amino acids   peptides and proteins Amino acids peptides and proteins Presentation Transcript

    • www.Examville.com Online practice tests, live classes, tutoring, study guides Q&A, premium content and more .
    • Amino Acids, Peptides and Proteins
    • The Proteins speak: “ We are the basis of structure and function of life; Composed of twenty amino acids, the building blocks; Organized into primary, secondary, tertiary and quaternary structure; Classified as simple, conjugated and derived proteins.”
      • AMINO ACIDS
      • group of organic compounds containing two functional groups:
      • amino group (-NH 2 )  basic
      • carboxyl group (-COOH)  acidic
      • General Structure of Amino Acids
      • H H
      • R C COOH R C COOH
      • NH 2 NH 3
      • General Structure Exists as ion
      • ⍺ - amino acids
      • amino
      • groups – attached to the
      • carboxyl same carbon Atom
      • ⍺ - carbon atom  binds to a side chain  represented by R (different for each of the 20 amino acids found in proteins)
      • Ionized forms  how they exist
      • Classification of Amino Acids
      • based on polarity
      • of the R group
          • 4 groups
          • Polarity  reflects the functional role of AA in protein structure
      • Non-polar AA
          • hydrophobic (water hating)
          • No charge on the ‘R’ group
          • Examples are:
          • Alanine Methionine
          • Leucine Phenylalanine
          • Isoleucine Tryptophan
          • Valine Proline
      • 3. Polar AA with (+) ‘R’ group
          • carries (+) charge
          • Examples:
          • Histidine Arginine Lysine
      • 4. Polar AA with (-) ‘R’ group
          • carries (-) charge
          • Examples:
          • Glutamic Acid Aspartic Acid
      • 2. Polar AA with no charge
      • on ‘R’ group
          • no charge on the ‘R’ group
          • possess groups  hydroxyl
          • sulfhydryl
          • amide
          • participate in hydrogen bonding of
          • protein structure
          • Examples:
          • Asparagine Glycine Cysteine Tyrosine Serine Threonine Glutamine
      • Physical Properties
      • 1. Solubility - soluble in water and insoluble in organic solvents
      • 2. Melting Points - melt at higher temperatures often 200 °C
      • 3. Taste
      • sweet (Gly, Ala, Val)
      • tasteless (Leu)
      • bitter (Arg, Ile)
      • Sodium Glutamate
      • – salt of Glutamic Acid – flavoring agent
      • 4. Optical Properties
      • - Assymetric  a carbon atom is
      • attached to 4
      • different groups
          • exhibiting optical isomerism
      • 4 distinct groups R
      • H - held by an
      • COOH ⍺-carbon
      • NH 3 ໋
      • All AA except Glycine possess optical isomers due to asymmetric ⍺-carbon atom
      • Some AA (Isoleucine, Threonine)  2 nd asymmetric carbon
      • D- and L- forms of AA based on
      • the structure of glyceraldehyde
      • CHO CHO
      • H C OH OH C H
      • CH 2 OH CH 2 OH
      • D-Glyceraldehyde L-Glyceraldehyde
      • R R
      • H C NH 2 H 2 N C H
      • COOH COOH
      • D-Amino Acid L-Amino Acid
      • The proteins are composed of L- ⍺ amino acids
      • 5. Amino acids as ampholytes
          • can donate a proton or accept a
          • proton
          • AA contain both acidic (-COOH) and basic (-NH 2 ) groups
      • Zwitterion or dipolar ion:
      • Zwitter
      •  from German word – means “hybrid”
      • Zwitter ion (or dipolar ion)
      •  a hybrid molecule containing ( + ) and ( - ) ionic groups
      • AA rarely exist in a neutral form with free carboxylic ( - COOH) and free Amino ( - NH 2 ) groups
      • Strongly acidic pH (low pH)  AA ( + ) charged (cation)
      • Strongly alkaline pH (high pH)  AA ( - ) charged (anion)
      • Each AA has a characteristic pH (e.g. Leucine, pH – 6.0), at which it carries both ( + ) and ( - ) charges and exist as zwitterion
      • Existence of an amino acid as Cation, Anion and Zwitterion
      • H
      • H ໋ R C COOH H ໋
      • NH 2
      • H Amino Acid H
      • R C COOH R C COO ¯
      • NH 3 ໋ H NH 2
      • Cation H ໋ H ໋ Anion
      • (low pH) R C COO ¯ (high pH)
      • NH 3 ໋
      • Zwitterion
      • (Isoelectric pH)
      • B. Chemical Properties
      • General Reactions  mostly due to the 2 functional groups
      • Reactions due to - COOH group
      • 1. AA from salts (-COONa) with bases
      • and esters (-COOR’) with alcohols
      • 2. Decarboxylation
      • - AA undergo decarboxylation to produce corresponding amines
      • 3. Reaction with Ammonia
      • - the carboxyl group of dicarboxylic AA reacts with NH 3 to form amide
      • Asparatic Acid + NH 3  Asparagine
      • Glutamic Acid + NH 3  Glutamine
      • Reactions due to -NH 2 group
      • 4. The Amino groups behave as bases and
      • combine with acids (e.g. HCl) to form
      • salts (-NH 3 + Cl ¯)
      • 5. Reaction with NINHYDRIN
      • - the ⍺-AMINO ACIDS react with Ninhydrin to form a purple, blue or pink colour complex (Ruhemann’s purple)
      • Amino acid + Ninhydrin  Keto acid + NH 3 + CO 2 + Hydrindantin
      • Hydrindantin + NH 3 + Ninhydrin  Ruhemman’s purple
      • Ninhydrin reaction – quantitative determination of AA and proteins
      • 6. Colour reactions of Amino Acids
      • - AA can be identified by specific colour reactions
      • Color Reactions of proteins / AA
      • Reaction Specific group or AA
      • Buiret Reaction Two peptide linkages
      • Ninhydrin Reaction ⍺ -Amino acids
      • Xanthoproteic Reaction Benzene ring of aromatic AA (Phe, Tyr, Trp)
      • Million’s reaction Phenolic Group (Tyr)
      • Hopkins – Cole Reaction Indole Ring (Trp)
      • 6. Sakaguchi Reaction Guanidino Group (Arg)
      • 7. Nitroprusside Reaction Sulfhydryl groups (Cys)
      • 8. Paulys’ test Imidazole ring (His)
      • 9. Sulfur test Sulfhydryl groups (Cys)
      • 10. Folin – Coicalteau’s Phenolic groups
      • test (Tyr)
      • 7. Transamination
      • - important reaction in AA metabolism
      • - transfer of an amino group from an amino acid to a keto acid to form a new AA
      • 8. Oxidative deamination
      • - AA undergo oxidative deamination to liberate free ammonia
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