4 Enzymes

Enzymes Enzymes are proteins. The active site is usually a hollow in the globular protein structure into which a substrate molecule can bond to the amino acid side chains through a variety of interactions including • Hydrogen bonding • Van der waals forces • Permanent dipole forces • Ionic interactions The interactions need to be strong enough to hold the substrate for long enough for the enzyme catalysed reaction to occur but weak enough for the product to be released CO2 – Hydrogen bonding Ionic interactions Van der waals forces active site substrate ser asp phe H3C Only substrate molecules with the right shape and correct positions of functional groups will fit and bind to the active site- called the lock and key hypothesis When the enzyme bonds to the active site it is called and enzyme-substrate complex stereospecific active site If the substrate is chiral then its likely that only one enantiomer will fit in the enzyme and so only one isomer will be catalysed Drugs as Enzyme Inhibitors Many drugs act as an enzyme inhibitor by blocking the active site. The inhibitor will often bind to the active site strongly so stopping the substrate attaching to the enzyme. (Some Inhibitors can also attach elsewhere on the enzyme but in doing so can change the shape of the active site which also stops its effectiveness) Computers can be used to help design such drugs