Amino acids

Cards (71)

  • What are the two functional groups of amino acids
    NH2 and COOH
    Amine and carboxylic acid
  • How many naturally occurring amino acids are there in the body
    20
  • What type of amino acids are found in the body
    • Alpha amino acids
    • It means that the NH2 is ALWAYS on the CARBON next to the COOH
  • Draw a general formula for alpha amino acids 

    ,
  • Are alpha amino acids CHIRAL
    • YES
    • One carbon has four different substituents
    • EXCEPT GLYCINE where R=H
  • Which enatiomer do alpha amino acids exist as in nature
    NEGATIVE enantiomer
  • How can amino acids be synthesised industrially
    • RCHO + NH4CN -> RCH(NH2)CH via NUCLEOPHILLIC ADDITION
    • RCH(NH2)CN + HCl + 2H2O -> RCH(NH2)COOH + NH4Cl
    • Hydrolysis and HCl is DILUTE
    • Need to REFLUX the reaction mixture
  • Is the product from amino acids being synthesised naturally optically active
    • NO
    • A racemic mixture is formed when CN- ions can attack from above and below the planar C=C bond with equal likelihood
    • An equal amount of each enantiomer is formed, so no net effect on plane polarised light
  • In what form do amino acids exist as solids
    • ZWITTERIONS
    • because it is an ionic lattice they have a HIGH melting and boiling point
  • What colour solids are most zwitterions at room temperature
    white solid
  • Do zwitterions dissolve in water
    • YES
    • But NOT in NON-POLAR solvents
    • Due to the ionic nature and polar bonds
  • define a zwitterion
    Ions which have both a permanent positive and negative charge, but are overall NEUTRAL
  • How do zwitterions occur in amino acids
    • COOH is DEPROTONATED -> COO-
    • NH2 is protonated -> NH3+
  • What happens to amino acids in ACIDIC conditions
    GAINS A PROTON ON NH2 GROUP
  • What happens to amino acids in ALKALINE conditions
    LOSES A PROTON FROM THE COOH GROUP
  • What is the peptide linkage
    -CONH-
  • What is a dipeptide
    Two amino acids bonded together
  • What name is given to chains of amino acids up to 50 amino acids
    polypeptides
  • What is the name given to chains of amino acids with more than 50 amino acids
    proteins
  • What are polypeptides used for
    • Enzymes
    • Wool
    • Hair
    • Muscles
  • What is the process called where polypeptides are broken down
    hydrolysis
  • What conditions are needed for hydrolysis to occur
    • 6 moldm^-3 HCl
    • Reflux for 24 hours
  • What is the primary structure of a protein
    the sequence of amino acids along the protein chain, bonded by Covalent bonds
  • How is the primary structure represented
    Sequence of 3 letters abbreviations of the amino acids
  • How can the primary structure of a protein be broken up
    • Hydrolysis
    • 6M HCl
    • 24 hour reflux
  • What is the secondary structure of a protein
    the shape of the protein chain
  • What are the two shapes an amino acid can form in the secondary structure
    • Alpha helix shape
    • Beta pleated sheets
  • How is the secondary structure held together
    • Hydrogen bonding
    • E.g between C=O and N-H groups
  • What is the tertiary shape of a protein
    • Alpha helix or beta pleated sheets is folded into a COMPLEX 3D shape
  • How is the tertiary structure held together
    • Hydrogen bonding
    • Ionic interactions between R groups
    • Disulfide bridges
    • Van der waals forces of attraction
  • Why is the tertiary structure important
    The shape of protein molecules is vital in their function e.g enzymes
  • How can amino acids be attracted to each other
    • Hydrogen bonding
    • Ionic interactions between groups on the side chain
    • Disulfide bridges -> 2 S atoms oxidised to form an S-S bond
  • What is wool
    • A protein fibre in the secondary structure of alpha-helix
    • held together by hydrogen bonds
  • What does wool's structure and bonding mean for wools properties
    • Can be stretched, as H bonds extend
    • You can release it after stretching it and it returns to its original shape
    • If you wash it TOO hot the H bonds PERMANENTLY break so the clothes will lose its shape
  • What is a TLC plate made of
    • Plastic sheet coated with silica, SiO2
    • This is the stationary phase
  • Describe how you would carry out THIN LAYER CHROMATOGRAPHY
    • spot the samples onto a pencil line a few cm above the base of the TLC plate
    • Place this in a beaker, with solvent level below the pencil line
    • Ensure there is a lid on the beaker to keep the inside saturated with solvent vapour
    • Wait until the solvent front is almost at the top of the TLC plate; then remove it from the beaker then analyse
  • Why does TLC separate amino acids
    • Solvent carries amino acids up the TLC plate
    • The rate of movement depends on the balance between the amino acid's affinity for the solvent and the affinity for the stationary phase
  • What do you often have to do to enable the amino acid to be seen on the chromatogram
    • Shine UV light
  • How do you calculate an Rf value
    • Distance moved by the substance / distance moved by solvent front
  • How can Rf values which amino acid is which
    • Compare the experimental Rf Values to known/accepted values in the same solvent