Enzyme Grade 8 Year 2011-2012

What Are Enzymes? Enzymes are proteins. Enzymes are catalysts that speed up chemical reactions Each enzyme catalyses one reaction They can be used again and again They are influenced by temperature and pH. proteins catalyst

Kinds of Enzymes Enzyme Reaction Amylase Breakdown starch (starch hydrolysis) Catalase Breakdown hydrogen peroxide (H2O2) to water and oxygen Cellulase Breakdown of cellulose in plant cell walls Lactase Hydrolysis of the milk sugar lactose Lipases Digestion of fats Proteases Digestion of protein

How Do Enzymes Work? Breaking large molecules into small ones e.g. starch is broken down into glucose Building up large molecules from small ones e.g. glucose are joined together into cellulose Converting one small molecule into another e.g. remove hydrogen from compounds during respiration

‘Lock and Key’ Model Enzymes work on substances called substrates. The reaction takes place on a part of the surface of the enzyme called the active site.

Effects of Temperature on Enzymes

Optimum Temperature The temperature at which the maximum rate of reaction occurs. Examples: Fungal and plant enzymes: 200 C Human enzymes : 37 0 C Some enzymes produced by bacteria : 900 C

Effects of pH on Enzymes Many enzymes work best in neutral conditions, but some prefer acidic and some alkaline conditions

Questions Which of the following enzymes would digest a fat? (a.) sucrase (b.) fatase (c.) protease (d.) lipase At high temperatures, the rate of enzyme action decreases because the increased heat (a.) changes the pH of the system (b.) alters the active site of the enzyme (c.) neutralizes the acids and bases in the system (d.) increases the concentration of the enzyme

An enzyme that hydrolyzes protein will not act upon starch An enzyme that hydrolyzes protein will not act upon starch. This fact is an indication that enzymes are (a.) hydrolytic (b.) specific (c.) catalytic (d.) synthetic Which chemical is classified as an enzyme? (a.) galactose (b.) lipid (c.) protease (d.) hydrogen peroxide Here are of some stages of an enzyme-controlled reaction   An enzyme-substrate complex is represented by diagram  (1.) A  (2.) B  (3.) C  (4.) D

Which statement best expresses the information represented in the graph shown? (a.)  The action of enzymes varies with pH.  (b.) A pH of 7 provides the optimum environment for digestive enzymes  (c.) Gastric juice is active at a pH extending from 0 to 12.  (d.) Acids have a pH greater than 7.