This document provides an overview of enzymes for a biology lesson. It defines enzymes as biological catalysts that are usually proteins and help speed up metabolic reactions in living organisms. It explains that enzymes work by lowering the activation energy of reactions and outlines several key points about how enzymes function, including that they have an active site that substrates bind to, and that temperature, pH, substrate concentration, and inhibitors can affect reaction rates. The objectives of the lesson are to explain enzymes, how they catalyze reactions, and factors that influence reaction rates.

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

2. 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

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

4. 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

5. Enzymes:- Are defined as a BIOLOGICAL catalyst i.e. something that speeds up a reaction. Up to 10 12 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

7. Amylase + starch substrate

8. 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

10. 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

11. “ 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 H 2 0 2 86-fold

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