Investigating Cells Enzymes Mr G Davidson

Investigating Enzymes Most chemical reactions occur very slowly at normal temperatures e.g. hydrogen peroxide breaks down very slowly at room temperature. Hydrogen peroxide (H2O2) Water (H2O) + Oxygen (O) 22 February, 2019 G Davidson

Investigating Enzymes If the temperature is increased the reaction speeds up, however this is not possible with living organisms. Therefore, a special chemical called a catalyst is used to speed the reaction up. Biological catalysts are called ENZYMES. Living cells produce enzymes to speed up reactions within the cells. 22 February, 2019 G Davidson

Investigating Hydrogen peroxide CATALASE is an enzyme which breaks down hydrogen peroxide to water and oxygen. If the enzyme is working properly, bubbles of oxygen are released. 22 February, 2019 G Davidson

Living Tissue Dead Tissue Each test tube contains 20ml hydrogen peroxide Living Tissue Dead Tissue Control 22 February, 2019 G Davidson

Investigating Hydrogen peroxide Results: The living tissues all produce bubbles, but the dead tissue doesn’t. Conclusion: Living tissues contain catalase which breaks down hydrogen peroxide. 22 February, 2019 G Davidson

Catalysts and Enzymes Catalysts are not changed by the reactions that they are acting on and so can be used again. There are many chemical reactions occurring in living cells at any one time. 22 February, 2019 G Davidson

Catalysts and Enzymes With the help of catalysts – enzymes, because the temperature is so low, these reactions would occur so slowly that life would be impossible. Enzymes themselves are NOT living – they are chemicals made of PROTEIN. 22 February, 2019 G Davidson

Catalysts and Enzymes It is possible to extract enzymes from living cells, and once this is done they can be dried and stored in powdered form. Most enzymes act within the cells in which they are produced. 22 February, 2019 G Davidson

Catalysts and Enzymes A small number do, however, work outside the cells, e.g. digestive enzymes. Some of the chemical reactions in living organisms involve the building up of large molecules. Others involve the breakdown of large, complex molecules into smaller simpler ones. 22 February, 2019 G Davidson

Amylase Starch is a large molecule made of hundreds of smaller glucose molecules joined together. An enzyme called amylase can break down starch and turn it into sugar. STARCH SUGAR AMYLASE 22 February, 2019 G Davidson

Testing Amylase Object: to investigate the enzyme amylase. Method: 1. Add 10ml starch solution to a test tube. 2. Add 2ml amylase solution. 3. Shake the tube to mix. 4. Test a drop for starch using iodine solution. 5. Test a drop for starch every 1 minute. Results: Conclusion: The iodine solution does NOT turn blue/black. Amylase breaks down starch to sugar. 22 February, 2019 G Davidson

Specificity Other enzymes act on different substances (SUBSTRATES) and so have no effect on starch. Each enzyme acts only on a specific substrate; other substances are not affected. The substance produced as a result of the reaction catalysed by an enzyme is called the PRODUCT. 22 February, 2019 G Davidson

Specificity SUBSTRATE ENZYME PRODUCT(S) Starch Amylase Simple sugar Fats Lipase Fatty acids & Glycerol Protein Pepsin Amino acids Glucose-1-phosphate Phosphorylase 22 February, 2019 G Davidson

Synthesis of Starch Starch may be synthesised from glucose. An enzyme is used to speed up the synthesis of starch. Potatoes contain large amounts of starch. Potato extract contains the enzyme phosphorylase which speeds up starch synthesis. PHOSPHORYLASE GLUCOSE-1-PHOSPHATE STARCH 22 February, 2019 G Davidson

Synthesis of Starch Object: To investigate the enzyme phosphorylase. Method: Set up the following: A B D C 1. Test the potato extract for the presence of starch. 2. Put 2 spots of glucose-1-phosphate into each of the hollows. 3. Add a drop of potato extract to each hollow and start the clock. 22 February, 2019 G Davidson

Synthesis of Starch After 4 minutes test A for the presence of starch. After the next 4 minutes test B and so on. Results: Conclusion: 22 February, 2019 G Davidson

Pepsin Activity The activity of an enzyme is affected by the pH of its surrounding medium. Pepsin is an enzyme produced in the stomach. It speeds up the breakdown of protein. 22 February, 2019 G Davidson

Pepsin Activity Copy and Complete the table using the results on your sheet. pH Initial Length (mm) Final Length Decrease in Length 2.5 50 3.7 4.9 7.0 8.4 9.0 22 February, 2019 G Davidson

Effect of pH on Enzyme Activity 22 February, 2019 G Davidson

Model Enzymes During an enzyme controlled reaction the substances involved – the substrates – become joined to the surface of the enzyme molecule. The chemical reaction then occurs very quickly. The spot on the enzyme molecule where the catalytic activity takes place is called the ACTIVE SITE. 22 February, 2019 G Davidson

Model Enzymes Enzyme molecules have many active sites over their surface. Only substrates that fit the active site exactly, react on the surface of the enzyme. Substrate molecules fit into these active sites like a key fitting into a lock. 22 February, 2019 G Davidson

Enzyme/substrate complex Model Enzymes Enzyme Substrate Enzyme/substrate complex Products 22 February, 2019 G Davidson

Model enzymes 22 February, 2019 G Davidson

Effect of Temperature on Enzyme Activity Because enzymes are proteins, they are affected by heat and the pH of the surrounding medium. At temperatures above 50oC most enzymes are permanently inactivated or DENATURED. Enzymes have a temperature at which they work best, and this is called the OPTIMUM temperature. 22 February, 2019 G Davidson

Effect of Temperature on Enzyme Activity Optimum Temperature 22 February, 2019 G Davidson

Investigating Urease Urease is an enzyme which catalyses the breakdown of urea. The activity of urease can be followed using a pH indicator to detect the presence of ammonia. Ammonia is a strong alkali. UREA + WATER AMMONIA + CO2 UREASE 22 February, 2019 G Davidson

Investigating Urease Test a little ammonium hydroxide with pH paper and note the colour. Place a little urea, water and 3 drops of indicator in a test tube. Add a pinch of urease and note what happens. 22 February, 2019 G Davidson

Inhibitors Some substances are able to stop or INHIBIT the activity of an enzyme. Repeat the urea experiment but add a few drops of silver nitrate to the test tube. The enzyme fails to work because the silver nitrate INHIBITS it. 22 February, 2019 G Davidson