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AS-U1-2.5 Proteins


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AS-U1-2.5 Proteins

  1. 1. Proteins?
  2. 2. Protein structure WALT: To understand the composition and various structures of proteins. Sunday, 28 September 2014 WILF: ~ Identify the basic structures of proteins. ~ Describe how proteins are formed from amino acids. ~ Describe the differences between the primary, secondary, tertiary and quaternary structures of proteins. Keywords Peptide bond Condensation reaction Polypeptide Hydrogen bonds Disulphide bonds Ionic bonds
  3. 3. Transcription What? The weak hydrogen bonds between the DNA strands are broken and the strands separate. One DNA strand is used as a template. Complementary bases pair up to the template, forming messenger RNA (mRNA). mRNA does not have the base thymine (T). Adenine (A) pairs with uracil (U) instead. Where? Inside the nucleus. mRNA
  4. 4. Translation Where? In the cytoplasm. tRNA Protein (polypeptide) ribosome amino acids mRNA The mRNA is decoded in groups of 3 (triplet or codon)
  5. 5. Amino acids Polymer: Protein or polypeptide Monomer: Amino acid All Amino Acids have an alkaline amino group (-NH2) and an acid carboxyl group (-COOH). There are just 20 naturally occurring Amino Acids, each with a different -R group.
  6. 6. The 20 naturally occurring amino acids.
  7. 7. Condensation reaction Molecule of water removed Peptide bond formed  dipeptide
  8. 8. Primary Structure The sequence of amino acids in the polypeptide chain. This structure determines shape and function of the protein. Genetic mutations.
  9. 9. Primary Structure
  10. 10. Secondary Structure Weak hydrogen bonds form between the polypeptide chains. Chain folds, 3d shape  Alpha helix Beta pleated sheet
  11. 11. Secondary Structure
  12. 12. The Alpha helix The Beta pleated sheet ------------ weak hydrogen bonds _________ strong covalent bonds
  13. 13. Tertiary Structure Further twisting and folding of secondary structures. Unique 3d structure. Disulphide bonds Ionic bonds Hydrogen bonds
  14. 14. Tertiary Structure
  15. 15. Quaternary Structure Further complexity. Pairs of chains may bind together or other inorganic substances may be incorporated into the molecule. (Prosthetic Groups) e.g. haemoglobin
  16. 16. Quaternary Structure
  17. 17. Primary structure Secondary structure Tertiary structure Quaternary structure Task 1: Fold A3 paper into four and assign a title for each. Cut out and stick the relevant statements and diagrams for each structure in the correct box. Task 2: Add further detail to each box by answering the questions.
  18. 18. Primary structure: 1. Explain how amino acids are joined together to form the primary structure. 2. Explain how one single change in the amino acid chain can affect the protein from carrying out it’s function. Secondary structure: 3. Explain how the weak hydrogen bonds are formed in the secondary structure of proteins. Tertiary structure: 4. Name and describe the different bonds that can form in the formation of a tertiary structure. 5. Explain how the 3D shape of a protein is important to its function. Quaternary structure: 6. Explain what a prosthetic group is and name an example.
  19. 19. Further complexity. Prosthetic Groups Further twisting and folding of secondary structures. Unique 3d structure. Weak hydrogen bonds form between the polypeptide chains. Alpha helix Beta pleated sheet The sequence of amino acids in the polypeptide chain.
  20. 20. Test for proteins The Biuret test. 1.Place a sample in solution in a test tube. 2.Add an equal volume of sodium hydroxide. 3.Add a few drops of dilute copper sulphate solution and gently mix. 4.Positive purple or negative blue.