Knowledge-2 PAE

• fibrous proteins form long parallel chains and have structural functions , such as collagen.
• proteins are made of monomers called amino acids
• Globular proteins are spherical and have many metabolic functions
• the general structure of amino acids is:

  • a unique R group (forms side(up) chain)
  • carboxyl group (COOH forms right side)
  • amine group (NH2 forms left side)
• Amino acids join via condensation reactions forming a peptide bond with water as a by-product.
• A dipeptide molecule is formed by the condensation of two amino acids.
• A polypeptide is formed by the condensation of many amino acids.
• A functional protein can contain one or more polypeptide chain.
• Enzymes are biological catalysts and bind to only a specific substrate that is complementary to its active site.
• enzymes lower activation energy required for a reaction
• Primary structure of proteins is the base sequence of amino acids in the polypeptide chain. This will determine the 3D shape of the protein and its active site.
• Secondary structure forms hydrogen bonds between amino acids leading to either pleating (beta pleated) or twist (alpha helix) in the polypeptide chain. Lots of hydrogen bonds form , does not involve r groups.
• Tertiary structure- the final specific 3D shape of the polypeptide is held in place by ionic bonds ,disulfide bonds and hydrogen bonds between r-groups.
• Quaternary structure is where separate polypeptides are linked together by covalent bonds.
• to test for proteins you can use the biuret test (changes colour from pale blue to lilac for positive).
• Competitive inhibitor:

  • competes for the active site of the enzyme
  • An active site blocked by the competitive inhibitor is not able to catalyze a reaction so the rate of reaction slows.
• Non-competitive inhibitor:

  • binds to the allosteric site of the enzyme leading to a change in specific shape of the active site, making the substrate no longer complementary.
  • no enzyme substrate complexes form.
• lock and key model:

  • the shape of the active site is complementary to the substrate molecule
  • the substrate fits into the active site exactly on collision
  • an enzyme substrate complex is formed
  • the reaction occurs
• induced fit model:

  • the shape of the active site of an enzyme is not fully complementary to the substrate molecule
  • when the substrate molecule collides with the active site , the enzyme molecule changes shape slightly to fit the substrate
  • reaction occurs