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Th1L04 Alpha helices and beta pleated sheets

Types of secondary protein structure
1. The folding/ coiling of a peptide chain
Alpha helix
1. Properties
  1. Amino acid side chains stick outwards
  2. Arrangement due to the strength of the hydrogen bonds b/w peptides
    1. Allows for best stabilisation energy between H-bonds
    2. between peptide bond cabonyl-O and H of N-H in every 4th peptide
      1. 0.54 nm distance between the troughs
2. Regular right-handed helix
  1. 3.6 residues/turn stabilised by H-bonds
  2. Rigid cylinder shape serves as architectural support for protein
3. Triple alpha helix
  1. Three chains
    1. H-bonds between alpha chains
  2. Found in fibrous proteins
  3. 3 residues/ turn
  4. Left-handed helix
  5. Amino acid chain
    1. gly - x - y- gly - x - y
      1. x = mainly proline
      2. y = mainly hydroxy-proline
4. Unique amino acids
  1. Proline
    1. Cannot go in the alpha helix because its structure
      1. aromatic ring
  2. Glycine
    1. Does not have an R group, which may explain why it is used in triple alpha helice
      1. Results in a more compact structure
Beta pleated sheet
1. Linear peptide chains
2. Hydrogen bonds between peptide bonds
3. Side chains in each strand alternately lie above and below the plane of the sheet
4. Types
  1. Antiparallel with a beta-hairpin bend
    1. Widespread in globular proteins
  2. Parallel with upper curve toward C terminus and lower curve toward N terminus
    1. Found in fibrillar proteins
      1. High tensile strength but not elasticity

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Th1L04 Alpha helices and beta pleated sheets

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	Created by Emma Allde about 9 years ago