2.3.2

  1. Recall that transient covalent bonds position the substrate in the enzyme active site to reduce the entropy of the system.

  2. Explain how weak non-covalent interactions (i.e. binding energy) reduce activation energy.

  3. Contrast Emil Fischer's lock-and-key model of enzyme specificity with the 'induced fit' hypothesis of enzyme catalysis.

  4. Define desolvation as it relates to binding energy.



  • Enzymes

    • How does an enzyme decrease the activation energy

      • 1) The formation between substrate and enzyme of transient covalent bond will activate the substrate and lower the activation energy, as well as decrease the entropy of the system

      • 1) these bonds are formed between chemical groups on the substrate, and chemical groups carries by amino acids on the enzyme in a site called the active site where catalysis takes place

      • 2) The formation of weak non-covalent bonds. results in a release of a small amount of energy.

      • 2) The summation of this small amount of energy form what is called a binding energy

      • 2) this energy that is resales is the main source of energy that is responsible for the decrease of the activation energy.

      • 2) On a reaction coordinate diagram, the binding energy is represent by the difference in free energy between the transition state, in the uncatalyzed and catalyzed reaction.

      • 3) The specificity of enzymes allow them to help and very different and specific bonds.

      • 3) EX Beta-galactosidase its an enzyme that catalyzes the hydrolysis of a family of molecules called Beta-galactosides.

      • 4) Another aspect to think about

      • 4) In the cell, a substrate is surrounded by molecules of water, and there is a formation of weak interaction between the water molecules and the substrate.

      • 4) Desolvation is the processed by which weak interaction between water and substrate are replaced by weak interactions between the substrate and enzyme

      • This weak interaction will contribute to binding energy and will facilitate catalysis


    • In 1890, Emil Fischer proposed a model that explains enzyme specificity.

    • He assumed that a substrate binds to the enzyme like a key to a lock

      • That model explain specificity but cannot explain the efficiency - In multiple examples, the enzyme, according to the Fischer model, will not help the catalysis at all.

    • in 1958, Daniel Koshland came with a different model called the induced fit

      • The model accounts for the deficiency of the Fischer model and is based on the two assumptions.

        • 1) You have optimum weak interaction, between the enzyme and the transition state

        • 2) Upon binding of the substrate to the enzyme, the enzyme changes conformation and that is the induced fit that optimized the position of the reacting groups in favor enzyme catalysis

  • Structural analogs

    • Molecules that have a chemical structure very similar to the substrate, but fail to react with the enzyme

  • Why is there an energy barrier that limits the reaction rate?

    • energy is required for several transformations that are needed for the reaction to proceed.

    • these were arrangement of bonds, formation of charge inside the active site of the enzyme, distortion of the reacting groups that are needed, etc.