Proteins (AQA AS Level)

Summary of all information in the Nelson Thornes AQA guide for AS Level Biology. Any boxes with a pencil icon inside are for displayed formulas (if the mindmap was to be printed out).

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  • Created on: 18-11-13 11:44
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  • Proteins
    • Most important molecules required for life.
      • Structural proteins
        • Fibrous proteins
          • Collagen
            • 3 individual polypeptide chains wound together line fibres in a rope, and linked with cross bridges.
              • Strong
              • Found in tendons - usded to move bones.
              • Points where polypeptides end and beginn are distributed throughout fibre so that there are no specific weak points.
      • Globular proteins
        • Enzymes - involved in almost every living process.
        • Carry out metabolic functions.
      • Transport proteins
        • Allow essential molecules/ions to move into/out of cells.
    • Monomers - amino acids
      • About 100 types of amino acid - 20 naturally occuring
      • Combine in condensation reactions, where a molecule of water is released and a peptide bond is formed.
        • Two combined amino acids: a dipeptide.
        • More than 2 combined amino acids - a polypeptide.
        • The peptide bond if formed between the  -C from the carboxyl group and the -N from the amino group.
        • The -OH from the carboxyl group and a -H from the amino group combine to make the molecule of water.
          • Products
            • Dipeptide + water
          • Reactants
          • Amino Acids
        • A peptide bond can be broken down by hydrolysis, involving the addition of a water molecule.
          • Poly/dipeptide + water => amino acids
        • Amino group - NH2
        • Carboxyl group              -COOH (acidic)
        • Variable R group - a variety of different chemical groups.
    • Primary Structure
      • Sequence of amino acids - the combination will be specific to the function of the protein.
        • Determines the protein's shape, as this depends on the bonds that will later be formed between certain amino acids.
    • Secondary Structure
      • Hydrogen bonds form between the positively-charged H of the -NH group, and the negatively-charged O of the -C=O group.
        • Causes the polypeptide chain to coil into an alpha-helix (or fold inot a beta-pleated sheet).
          • 3D
    • Tertiary Structure
      • The polypeptide chain is coiled (or folded) even more to produce the complex, unique shape of the protein.
        • This structure is maintained by various bonds:
          • Disulfide bonds (fairly strong)
          • Ionic bonds between the carboxyl and amino groups not involved in froming peptide bonds.
            • Weaker than disulfide bonds and easily broken down by changes in pH.
          • Hydrogen bonds
            • Numerous, but weak.
        • 3D - shape allows to recognise/be recognised by other molecules + interact. Final structure for some proteins.
    • Quaternary Structure
      • Multiple polypeptide chains (in the tertiary structure) linkled together by bonds.
        • Often include non-protein groups (prosthetic groups).
      • Large proteins - complex molecules.
      • Test for proteins
      • Add equal volume of sodium hydroxide to the sample in a test tube.
        • Add few drops of copper(II) sulfate solution (0.05% concentration) and mix gently.
          • Purple colouration indicates presence of PEPTIDE BONDS.
          • If solution remains blue, no PEPTIDE BONDS present.


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