They have an active site where the reaction takes place. • Enzymes lower activation energy of the reaction they catalyse. RUBISCO is the abundant protein in the whole biosphere As molecules react, they become unstable, high energy intermediates. But they are in this transition state only momentarily.
Energy is required to raise molecules to this transition state and this minimum energy needed is called the activation energy . This could be explained schematically by ‘boulder on hillside’ model of activation energy (Figure . ). .
. Lock and Key Mechanism of Enzyme In a enzyme catalysed reaction, the starting substance is the substrate. It is converted to the product. The substrate binds to the Energy in the reaction Enzyme Reactant Product Time Activation energy without enzymes Activation energy with enzymes This graph shows the activation energies of a reaction with and without enzymes Figure .
: Activation energy - - . . PM Coenzyme Apoenzyme Catalytic site Cofactor Holoenzyme Figure . : Enzyme components • Inorganic ions help to increase the rate of reaction catalysed by enzymes.
Example: Salivary amylase activity is increased in the presence of chloride ions. • Prosthetic groups are organic molecules that assist in catalytic function of an . . Classification of Enzymes Enzymes are classified into six groups based on their mode of action .
Enzymes Mode of action General scheme of reaction Example Oxidoreductase Oxidation and reduction (redox) reactions A red + B ox A ox + B red Dehydrogenase Transferase Transfer a group of atoms from one molecule to another A – B + C A + C – B Transaminase, phosphotransfer- ase Hydrolases Hydrolysis of substrate by addition of water molecule A – B + H O A – H + B – OH Digestive enzymes Isomerase Control the conversion of one isomer to another by transferring a group of atoms from one molecule to another A – B – C A – C – B Isomerase Lyase Break chemical bond without addition of water A – B A + B Decarboxylase Ligase Formation of new chemical bonds using ATP as a source of energy