YEAR 12 - AS Biology29th November 2005 Enzymes Mr Potter
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:- • 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
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
Substrate concentration Initially rate increases with substrate conc. Reaction rate factors
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