Protein Structure

Cards (40)

  • Proteins in any of their functional, folded conformations are called native proteins.
  • Stability is the tendency to maintain a native conformation
  • The unfolded stated of a protein is characterized by a high degree of conformational entropy.
  • The rigid peptide bonds limit the range of conformations possible for a polypeptide chain.
  • In an a-helix structure amino acid residues protrude outward from the helical backbone.
  • Each helical turn in an a-helix includes 3.6 amino acid residues
  • Dihedral angles in the backbone, determines a-helix conformation.
  • Extended left-handed a-helices are less stable.
  • One fourth of all amino acid residues in proteins are found in a-helices.
  • Glutamate residues repel each other, thus preventing formation of a-helix
  • The bulk and shape of ser, asn, thr, and cys residues can destabilize an a-helix if they are close together.
  • Proline and Glycine will not be seen in an a-helices
  • Fibrous proteins are polypeptide chains arranged in long strands or sheets.
  • Globular proteins are polypeptide chains folded into a spherical or globular shape.
  • All fibrous proteins are insoluble in water.
  • Silk fibroin is an example of B conformation
  • B-conformation characteristics soft, flexible filaments.
  • Keratin is a right-handed a-helix
  • Keratin is rich in hydrophobic residues.
  • In keratin, cross-links stabilizing quarternary structure are disulfide bonds.
  • How can fibrous proteins strength be enhanced? By covalent cross-links
  • Collagen is left-handed and has 3 amino acid residues per urn.
  • Gelatin is derived from collagen
  • Collagen contains a lot of proline and glycine residues.
  • Proline permits the sharp twisting in collagen.
  • As you get older, connective tissue becomes more rigid and brittle dued to accumulated covalent cross-links.
  • Silk fibroin is rich in alanine and glycine residues.
  • Silk does not stretch, because the B conformation is already highly extended.
  • A loss of 3-D structure that causes loss of function is called denaturation.
  • Circular dichroism measures the amount of helical structure in a protein.
  • Urea disrupts hydrogen bonds.
  • Organic solvents, urea, and detergents disrupt hydrophobic aggregation of nonpolar amino acid side chains, which produces the stable core of globular proteins.
  • Extremes of pH alter the net charge on a protein, causing electrostatic repulsion and the disruption of some hydrogen bonding.
  • Protein precipitation is a consequence of protein aggregate formation as exposed hydrophobic surfaces associate.
  • Unfolded states have a high degree of conformational entropy and high free energy.
  • Chaperones facilitate correct folding
  • Peptide C-N bonds have partial double bond character, meaning they cannot rotate freely.
  • B turns connect the ends of two adjacent segments of antiparallel B sheets.
  • Glycine and Proline are often found in B-Turns.
  • The light-absorbing entity is also referred to as chromophore.