YEAR 12 - AS Biology 29th November 2005 Enzymes dr shabeel pn

Lesson Objectives Enzyme unit overview What are they? How they work Activation energy What controls their activity Rates of reaction Substrate/enzyme concentrations Temperature, pH Enzyme inhibitors Practical to demonstrate “Catalase” activity in different tissue samples

Previous related topics covered? Enzyme controlled reactions? Proteins? Lipase, protease, pectinase, amylase etc? “Lock & Key” molecular structures?

By the end of the unit you should be able to:- Explain enzymes as Globular Proteins which act as catalysts Explain their catalytic action in terms of lowering activation energy Describe examples of enzyme-catalysed reactions Discuss factors affecting reaction rates and inhibition Describe how to investigate these effects experimentally

Enzymes:- Usually end in ‘…ase’. Are defined as a BIOLOGICAL catalyst i.e. something that speeds up a reaction. Up to 1012 fold Usually end in ‘…ase’. Discovered in 1900 in yeasts. Some 40,000 in human cells Control almost every metabolic reaction in living organisms Are globular proteins coiled into a very precise 3-dimentional shape with hydrophilic side chains making them soluble Possess an active site such as a cleft in the molecule onto which other substrate molecules can bind to form an enzyme-substrate complex Once the substrate has been either synthesised or split, enzymes can be re-used. Do not ‘create’ reactions Widely used in industrial cleaning Often require co-factors (co-enzymes) to function – metal ions, or vitamin derivatives

Amylase + starch substrate

How do enzymes work? Reaction Mechanism In any chemical reaction a substrate is converted into a product. In an enzyme catalysed reaction the substrate first binds to the active site of the enzyme to form the enzyme-substrate complex

Molecule Geometry Substrate molecule fits into the enzyme like a lock & key. Enzyme shape distorts or it changes other factors to make the reaction happen

“Activation Energy” In a ‘natural’ reaction the product has a lower energy than the substrate so equilibrium will take it in the direction of the product. However there is an energy ‘barrier’ to be overcome Enzymes lower the activation energy required to bring about a reaction. EG catalase reduces the activation energy for the reduction of H202 86-fold

Reaction rate factors Substrate concentration Initially rate increases with substrate conc.