Sucrose (C 12 H 22 O 11 ) Glucose (C 6 H 12 O 6 ) Fructose (C 6 H 12 O 6 ) Sucrase

 The initial energy required to start a chemical reaction  Activation energy is often supplied in the form of heat from the surroundings

 A catalyst is a chemical agent that speeds up a reaction without being consumed by the reaction  Works by lowering activation engery

Fig Progress of the reaction Products Reactants ∆G is unaffected by enzyme Course of reaction without enzyme Free energy E A without enzyme E A with enzyme is lower Course of reaction with enzyme

 Enzyme – biological catalyst; substrate specific; reusable  Substrate – the specific reactant for an enzyme; binds to enzyme  Active site – site on enzyme to which substrate binds – substrate specific

 Very specific  1 type of enzyme works with one substrate  Fit together perfectly

 When substrate and enzyme join the enzyme shape is modified  The enzyme wraps around the substrate  It is not rigid like metal

Fig Substrates Enzyme Products are released. Products Substrates are converted to products. Active site can lower E A and speed up a reaction. Substrates held in active site by weak interactions, such as hydrogen bonds and ionic bonds. Substrates enter active site; enzyme changes shape such that its active site enfolds the substrates (induced fit). Active site is available for two new substrate molecules. Enzyme-substrate complex