enzymes

• enzymes are biological catalysts, meaning they alter the rate of biochemical reactions, whilst remaining unchanged.
• all reactions need an initial input of energy. this is activation energy. enzymes reduce activation energy, which conserves energy and speeds up the reaction
• the active site on an enzyme has a particular shape determined by the sequence of amino acids that forms on the enzyme.
• enzymes only work with one type of substrate. the substrate fits exactly into the active site. there is a chemical attraction (affinity) between enzyme and substrate.
• induced fit is when the active site is flexible and slightly alters its shape when the substrate enters. this close fit ensures the active site is in very close contact with the substrate. end products are released because there is low affinity with the active site. the enzyme will return to its original conformation
• to function efficiently, enzymes must have optimum pH, temperature, supply of substrate (substrate concentration), and inhibitors
• enzymes are controlled by inhibitors, which are substances that decrease the rate of enzyme controlled reactions. 3 mechanisms of enzyme inhibition are competitive, non-competitive, and feedback.
• competitive inhibitors compete with a substrate for the active site of an enzyme. these inhibitors are a similar structure to the substrate so can block an active site. this decreases the rate of chemical reactions. competitive inhibition can be reversed by increasing substrate concentration.
• non-competitive inhibitors become attached to an allosteric site on an enzyme. this alters the shape of the enzyme, and therefore the active site, so that it can no longer combine with the substrate molecule. this is irreversible.
• feedback inhibition occurs when the end product in the metabolic pathway reaches a critical condition. the end product then inhibits an earlier enzyme, blocking the pathway, and so prevents further synthesis of the end product.