Underlying Biology

• Describe enzymes

  Enzyme molecules are made of different types of protein. On the surface of an enzyme, there is a dip where the active site is found. These active sites have different shapes which are due to the chemical structure and bonding between the amino acids in the polypeptide chains.
• Describe affinity

  Enzymes have substrates which are complementary molecules which fit inside the active sites. Substrates have an affinity to these active sites, this means that they have a chemical attraction to them.
• Describe induced fit

  The active site of an enzyme is flexible and can change its shape to fit the substrate molecule more effectively, this process is called induced fit.
• Describe orientation

  When two or more substrates are involved, the shape of the active site determines the orientation of the reactants.
• Describe biological catalysts

  Enzymes are biological catalysts which means they can speed up reactions by lowering the activation energy required for successful reactions. This also means they allow these reactions to occur at lower temperatures. As the are catalysts, thus also means that they can take part in the reaction but will not be changed by or be used up in the reaction.
• Describe the regulation of metabolic pathways

  Metabolic pathways can be controlled by regulating the enzymes that take part in them. One way this can happen is by using an inhibitor. An inhibitor is a substance which lowers the rate of enzyme-controlled reactions. There are two types of inhibitor: competitive and non-competitive.
• Describe competitive inhibition

  Competitive inhibitors have a similar shape to the complementary substrate so they can bind to the active site, blocking the substrate and reducing the reaction rate. Increasing substrate concentration can reverse competitive inhibition as the substrate molecules outnumber the competitive inhibitor molecules, stopping them from competing.
• Describe non-competitive inhibition

  Non-competitive inhibitors bind away from the active site which changes the shape of the enzyme and its active site indirectly. This prevents substrate molecules from binding, decreasing the reaction rate. Non-competitive inhibition cannot be reversed by increasing substrate concentration.
• Describe feedback inhibition

  Another type of regulation is feedback inhibition. Feedback inhibition occurs when the concentration of the end product reaches a critical level and then it binds to the first enzyme in the pathway, regulating and slowing down the first steps of conversion of reactants in the pathway.