Enzymes

Enzymes

1. Terms

   • Enzyme
     • An enzyme is a biological catalyst. It is a substance that acts as a catalyst in living organisms, regulating the rate at which chemical reactions proceed without itself being altered in the process.
       • A globular protein that increases the rate of biochemical reaction by lowering the activation energy threshold (i.e a biological catalyst)
   • Catalyst
     • A catalyst is a substance or factor to speed up our (chemical or biological) processes/reactions without taking part in them.
   • Substrate
     • Reactant in a biochemical reaction
   • Kinetic theory
     • Matter is made of particles, and the particles move. If the matter is solid the particles will still vibrate.
       • Liquid particles will move and as the temperature increases, the particles will move faster and crash into each other more regularly. Meaning, the higher the temperature is, the faster the particles are moving.
   • Denature
     • Any heating that results in a protein to change its shape will loose its functions and become denatured.
     • Enzymes become denatured when a change in structure means a change in its active site. If the active site changes shape the substrate is no longer able to bind to it.

2. 1. Enzymes have an active site to which specific substances bind

   • Lock and key model
     • The specific action of an enzyme with a single substrate can be explained using a Lock and Key analogy first postulated in 1894 by Emil Fischer. In this analogy, the lock is the enzyme and the key is the substrate. Only the correctly sized key (substrate) fits into the key hole (active site) of the lock (enzyme).
       • Can be used to explain how you split or combine something
     • The induced-fit model better explains enzyme activity
       • As the substrate approaches the enzyme, it induces a conformational change in the active site - it changes chape to fit the substrate. This stresses the substrate, reducing the activation energy of the reaction

3. 2. Enzyme catalysis involves molecular motion and the collision of substrates with the active site

   • The coming together of a substrate molecule and an active site is known as a collision. Most enzyme reactions occur when the substrates are dissolved in water. All molecules dissolved in water are in random motion, with each molecule moving separately. Collisions are the result of random movements of both substrate and enzyme. Also, successful collisions are ones in which the substrate and active site happen to be correctly aligned to allow binding to take place.
     • Denaturation of proteins by heat or by deviation of pH from the optimum
       • A denatured protein does not normally return to its former structure - the denaturation is permanent. ENZYMES ARE PROTEINS AND DENATURATION IS A KEY TO HOW ENZYME ACTIVITY IS AFFECTED BY TEMPERATURE AND pH.
         • Because... Heat causes vibrations within the molecule which breaks intermolecular bonds and interactions. This action equals denaturation.

4. 3. Temperature, pH and substrate concentration affect the rate of activity of enzymes

   • Low temperature result in insufficient thermal energy for the activation of a given enzyme-catalysed reaction to be achieved
     • Increasing the temperature will increase the speed and motion of both enzyme and substrate, resulting in higher enzyme activity (THIS IS BECAUSE A HIGHER KINETIC ENERGY WILL RESULT IN MORE FREQUENT COLLISIONS BETWEEN ENZYME AND SUBSTRATE)
       • Higher temperatures will cause enzyme stability to decrease, as the thermal energy disrupts the hydrogen bonds holding the enzyme together. THIS CAUSES THE ENZYME TO LOSE ITS SHAPE (PARTICULARLY THE ACTIVE SITE), RESULTING IN A LOSS OF ENZYME ACTIVITY (DENATURATION)
         • Changing the pH alter the charge of the enzyme, which in turn will change protein solubility and may change the shape of the molecule. Changing the shape or charge of the active site will diminish its ability to bind to the substrate, halting enzyme function

5. 5. Immobilized enzymes are widely used in industry

   • Detergents contain proteases and lipase to help breakdown protein and fat stains
     • Enzymes are used to break down the starch in grains into BIOFUELS that can be combusted
       • In the textiles industry enzymes help in the process of fibres; polishing cloth to make it appear more shiny. Also, paper production uses enzymes to help in the pulping of wood
         • Advantages of enzyme immobilization: CRSS.