Polymers and Life (OCR B- New Spec)

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  • Created on: 13-12-16 13:19
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  • Polymers and Life
    • DNA and RNA
      • In DNA the bases are Adenine, Thymine, Cytosine and Guanine. In RNA the thymine is replaced by Uracil.
        • Adenine with Thymine and Cytosine with Guanine
      • Section of DNA unzips. RNA nucleotides are joined together. Once copied the DNA reforms and the mRNA produced leaves the nucleus.
    • Proteins
      • Amino Acids are made up of an amine group, a carboxylic acid, a hydrogen and an R group surrounding a central carbon
      • Due to being bifunctional the groups can interact with each other.
        • The proton donating         -COOH and the proton accepting        -NH? cause it to be a zwitterion.
          • Zwitterions contain both a negatively charged group and a positively charged group.
        • Aqueous solution of amino acids consists of zwitterions.
          • These are generally neutral solutions unless the R group contains an extra -COOH or -NH?
          • The addition of acid or alkali tends to have no effect as the zwitterions buffer the effect.
      • As amino acids have 4 different groups around the carbon they show optical isomerism
        • optical isomerism arises when the mirror image cannot be superimposed onto each other.
        • Molecules that show optical isomerism in tetrahedral shapes are known as chiral molecules
        • Optical isomerism can also be referred to as enantiomers
      • Two amino acids can be joined by a condensation reaction with the -COOH and the -NH?. This forms a peptide link.
        • A polypeptide chain can be hydrolysed to reform the amino acids
      • Primary structure is the specific order of amino acids in a polypeptide chain
        • Secondary structure - coiling of the chain into a helix or into a sheet held together by hydrogen bonds
          • Tertiary structure - further folding of the structure held together by intermolecular bonds, ionic bonds and covalent bonds
      • Enzymes
        • Characteristics
          • Catalysts
            • Provide an alternate route with a lower activation enthalpy
          • Highly specific
            • Due to the tertiary structure must match the structure of the subrate exactly
              • Sometimes one stereoisomer will fit where another will not
          • sensitive to pH
            • Enzymes usually contain ionisable groups that are affected by pH.
            • Example:       -COOH if the pH is raised it will turn to       -COO¯  and the enzyme will be not be abelt o function properly
          • Sensitive to temperature
            • Some bonds in the tertiary structure are weak and only need a small temperature increase to break.
            • An enzyme will be inactive or denatured if its shape is changed too much
              • sensitive to pH
                • Enzymes usually contain ionisable groups that are affected by pH.
                • Example:       -COOH if the pH is raised it will turn to       -COO¯  and the enzyme will be not be abelt o function properly
          • Subjective to competitive inhibition
            • Competitive inhibitors bind to the enzyme but cannot be catalysed and therefore block the enzyme from substrates
    • Carboxylic Acids, Phenols and Esters
      • Carboxylic acids react with carbonates in an acid base reaction were the CO? is a base.
      • Carboxylic acids and phenols are strong enough acids to react with strong bases to form salts. Alcohols are not.
      • Esters are formed by the reaction of alcohols and carboxylic acids heated with concentrated sulfuric acid. This is known as esterification.
        • Condensation reaction. Joining two molecules together with the removal of water.
        • Naming esters: the alcohol is classed as the side group and the acid has the ending -oate
        • The -OH in phenol is less reactive than in a carboxylic acid so an acid anhydride is needed for esterification, under alkaline conditions.
    • Amines
      • Amines resemble ammonia molecules with alkyl groups replace one or all the hydrogen atoms.
      • Properties are similar to ammonia but modified due to alykl groups
        • The lone pair of electrons is responsible for amines being soluble in water and acting as bases
          • Amines with larger alkyl groups are less soluble in water
        • Due to the lone pair it can act as a base: able to donate a pair of electrons
    • Amides
      • Derivatives of carboxylic by replacing the -OH with -NH?
      • Polyamides are formed by the condensation of diamines and dicarboxylic acids
        • Usually named nylons
          • First digit is for the diamine and second is the dicarboxylic acid
          • Nylon- 6,10 is made form 1,6-diaminohexan and decanedioc acid
    • Hydrolysis of esters and amides
      • Hydrolysis of esters with acid occurs as expected but is a reversible reaction so never goes to completion
      • Hydrolysis of esters with an alkali produces a carboxylate salt instead of a carboxylic acid but goes to completion so is preferred
      • Hydrolysis of amides with acid must be heated and have differing outcomes depending on the state of amide
        • For primary amides the acid forms a cation with the ammonia
        • For secondary amides an amine salt is formed
      • Hydrolysis of amides with an alkali, a carboxylate ion and the amine is formed.

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