2 Enzymes Learning Objectives To describe the optimum conditions for enzymes.To describe the function of enzymes in the digestive system.To explain that enzymes are specific, using the lock and key model.
3 Your cells are chemical factories.. 100’s chemical reactions are happening in cells all the timeNeed to be very controlledCatalysts can help alter the speed of a chemical reactionThey are not change or used up in the reactionCatalysts are specific to one type of reactionEnzymes are biological catalysts – they help speed up chemical reactions in our cellsThey are Proteins!
4 Jobs for enzymesEnzymes catalyse only one type of reaction each – ie they are SPECIFICThey bind to specific reactants known as substrates.Enzymes are involved in:Building large molecules from lots of smaller onesChanging one molecule into anotherBreaking down large molecules into smaller ones
6 What are enzymes made of? Boardworks GCSE Additional Science: BiologyEnzymesWhat are enzymes made of?Enzymes are protein molecules, and so are made up of amino acids. Most enzymes contain between 100 and 1,000 amino acids.These amino acids are joined together in a long chain, which is folded to produce a unique 3D structure.
7 Examples where enzymes are used: DNA replication: Help copy a cell’s DNA before it divides by mitosis or meiosis.Protein Synthesis: Hold amino acids in place and form the bonds between them.Digestion: Help to digest food molecule's
8 How do they work?Every enzyme has something called an active site, this is the region where the substrate joins onto. Enzymes only attach to specific substrate molecules. Enzymes only work when there is an exact fit with the substrate. This is known as the lock and key mechanism.
9 Boardworks GCSE Additional Science: Biology Enzymes The lock and key modelTeacher notesThis four-stage animation demonstrates the principles of the ‘lock and key’ model. While showing the animation, the specific shape of the active site could be highlighted.Suitable prompts could include:What is special about the shape of the active site?Is the enzyme the ‘lock’ or the ‘key’?
12 Optimum TemperatureAs the temperature increases, so does the rate of reaction. But very high temperatures denature enzymes.The graph shows the typical change in an enzyme's activity with increasing temperature.The enzyme activity gradually increases with temperature until around 37ºC, or body temperature.Then, as the temperature continues to rise, the rate of reaction falls rapidly, as heat energy denatures the enzyme
14 Optimum pH Changes in pH alter an enzyme’s shape. Different enzymes work best at different pH values.The optimum pH for an enzyme depends on where it normally works.For example, intestinal enzymes have an optimum pH of about 7.5.Enzymes in the stomach have an optimum pH of about 2.
15 Denatured enzymesEnzymes can be denatured by high temperatures and extremes of pH. Both high temperatures and extremes of pH change the bonds between amino acids in the enzyme, so changing its shape.Enzymes work slowly at low temperatures too – but this is because the substrate molecules have less energy and move into the active site more slowly. This is not a permanent change.
16 There is one more way to affect the rate of an enzyme controlled reaction
17 Measuring the Rate of an Enzyme Controlled Reaction Amylase- Enzyme that breaks down starchStarch- Substrate for amylaseIodine- Turns a blue black colour when starch is present.Using these chemicals plus any lab equipment of your choice describe a simple method to measure the rate of an enzyme controlled reaction.Write it as numbered steps for how you would do it.
18 How you would do itAmylase catalyses the breakdown of starch, so you can time how long it takes for the starch to disappear.To do this. Take a drop of amylase and starch mixture, and put it onto a drop of iodine solution on a spotting tile. Record the colour change- it’ll turn blue black if starch is present. Note the time when the iodine solution no longer turns blue-black- the stanch has then been broken down by the amylase.You can use the times to compare reactions rates under different conditions.
19 We know how to measure the rate, but then how can we change the rate? To investigate the effect of temperature- put test tubes into water baths at a range of temperatures.pH- Different pH buffersSubstrate concentration- vary concentrations of starch.
20 Questions What is a catalyst? Explain why enzymes are needed in the body.How can the rate at which enzymes work be altered?Small molecules often dissolve easily in water then larger ones. Explain as fully as you can why enzymes are used in laundry detergents. Include proteins, catalysts and enzymes in your answer.