3 What’s the missing link? Boardworks GCSE Additional Science: BiologyEnzymesWhat is the link between digestion, photosynthesis, respiration and DNA replication?They all depend on enzymes.
4 Boardworks GCSE Additional Science: Biology What are enzymes?Boardworks GCSE Additional Science: BiologyEnzymesEnzymes are biological catalysts – they speed up the chemical reactions that take place inside all cells, but without being used up in the process.There are many thousands of different types of enzyme, and each one catalyzes a different reaction.Cells create enzymes based on instructions carried in the cell’s genes.
5 What are enzymes made of? Boardworks GCSE Additional Science: BiologyEnzymesEnzymes 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.Different types of enzymes have different shapes and functions because the sequence and type of amino acids in their structure is different.
6 Boardworks GCSE Additional Science: Biology Enzymes: true or false?Boardworks GCSE Additional Science: BiologyEnzymesTeacher notesThis true-or-false activity could be used as a plenary or revision exercise on enzymes, or at the start of the lesson to gauge students’ existing knowledge of the subject matter. Coloured traffic light cards (red = false, yellow = don’t know, green = true) could be used to make this a whole-class exercise.
8 Boardworks GCSE Additional Science: Biology Fussy enzymes?Boardworks GCSE Additional Science: BiologyEnzymesWhy are enzymes so specific in their reactions?Teacher notesThis illustration contains several discussion points relating to enzymes, including:ThermostatDifferent enzymes have different optimum temperatures. Beyond their optimum temperature enzymes denature (breakdown). The thermostat in the illustration is set to a high temperature, and most of the enzymes seem uncomfortably hot.ArgumentsThe shape of an enzyme’s active site determines which reactants it can bond with. In this illustration, incompatible enzyme–reactant pairs are shown either arguing or ignoring each other.‘The happy couple’Enzymes and reactants that are compatible are said to fit together like a ‘lock and key’. The happy couple shown in the bottom left of the illustration have corresponding shapes, and seem to be reacting well to each other in the warm environment.
9 Why are enzymes so specific? Boardworks GCSE Additional Science: BiologyEnzymesEnzymes are very specific about which reactions they catalyze. Only molecules with exactly the right shape will bind to the enzyme and react. These are the reactant, or substrate, molecules.The part of the enzyme to which the reactant binds is called the active site.This is a very specific shape and the most important part of the enzyme.Photo credit: JC Revy / Science Photo LibraryThe image shows a molecular computer graphics image of ribonuclease A, an enzyme involved in the destruction of messenger RNA (mRNA) in the cytoplasm of bacteria. At left is its substrate, shifted away from the active site. Enzymes are biological catalysts, proteins that speed up the rates of reactions within cells. Each enzyme is specific for a particular reaction; interaction occurs (typically as a weak bond) between an active site on the enzyme & a reactant (or substrate) due to the arrangement of mutually attractive groups of atoms. This image displays the molecular surface (blue) & polypeptide chain: colours are used to represent the polarity of constituent amino acids.
10 What happens at the active site? Boardworks GCSE Additional Science: BiologyEnzymesIn the same way that a key fits into a lock, so a substrate is thought to fit into an enzyme’s active site. The enzyme is the lock, and the reactant is the key.++↔↔enzymereactant+enzyme–reactant complex↔products
11 Boardworks GCSE Additional Science: Biology The lock and key modelBoardworks GCSE Additional Science: BiologyEnzymesTeacher 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 Why do enzymes speed up reactions? Boardworks GCSE Additional Science: BiologyEnzymesEnzymes speed up reactions by lowering the activation energy (Ea) of a reaction. The activation energy is the energy needed to start a reaction.Different reactions have different activation energies.reaction (time)energy (kJ)Ea without enzymeEa with enzymeTeacher notesSee the Boardworks GCSE Additional Science Chemistry Changing Reaction Rates presentations for more information on activation energy.
13 Factors affecting enzymes Boardworks GCSE Additional Science: BiologyEnzymesThe rate of enzyme-catalyzed reactions depends on several factors. What are some of these?Factors that affect the rate of a reaction include:temperaturesubstrate concentrationpHsurface areaenzyme concentrationpressure.All enzymes work best at only one particular temperature and pH: this is called the optimum.Different enzymes have different optimum temperatures and pH values.
14 Factors affecting enzymes Boardworks GCSE Additional Science: BiologyEnzymesIf the temperature and pH changes sufficiently beyond an enzyme’s optimum, the shape of the enzyme irreversibly changes.This affects the shape of the active site and means that the enzyme will no longer work.When this happens the enzyme is denatured.denaturednormalheatpHThe information on this slide is higher tier for OCR 21st Century GCSE Additional Science and OCR Gateway GCSE Additional Science.
15 Enzymes and temperature Boardworks GCSE Additional Science: BiologyEnzymesTeacher notesThis five-stage animation could be used as a precursor to running the experiment in the lab, or as a revision exercise.
16 Temperature and reaction rate Boardworks GCSE Additional Science: BiologyEnzymesAs the temperature increases, there are more collisions between enzymes and reactants. This increases the rate of reaction.At a certain point, the temperature gets too high and the enzymes are denatured. The enzymes can no longer bind with reactants.We can work out the Q10 for any reaction over a 10°C interval with the following formula:Teacher notesStudents may need to be reminded that the Q10 temperature coefficient is the measure of the rate of change of a system as a result of increasing the temperature by 10°C.You might like to have students apply this equation to the reaction on the previous slide. Show them either the graph or the table from the final stage of the animation and ask them to find the Q10 of the reaction.The information on this slide is higher tier for OCR 21st Century GCSE Additional Science and OCR Gateway GCSE Additional Science.rate at higher temperatureQ10 =rate at lower temperature
17 Boardworks GCSE Additional Science: Biology Enzyme inhibitorsBoardworks GCSE Additional Science: BiologyEnzymesTeacher notesThis four-stage animation shows how competitive and non-competitive inhibitors block the action of enzymes by either binding to, or altering the shape of, their active site.
18 Identifying enzyme terms Boardworks GCSE Additional Science: BiologyEnzymesTeacher notesThis matching activity could be used as a plenary or revision exercise on enzymes. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.
20 Boardworks GCSE Additional Science: Biology GlossaryBoardworks GCSE Additional Science: BiologyEnzymesTeacher notesactivation energy – The energy needed to start a chemical reaction.active site – The part of the enzyme into which the reactant molecule fits.catalyst – A substance that changes the rate of a reaction without being used up.denatured – The state of an enzyme when it has been irreversibly damaged and has changed shape.enzyme – A biological catalyst.inhibitor – A molecule that decreases the rate of enzyme-catalysed reactions.lock and key – A model of how enzymes work and the importance of their shape.optimum – The temperature and pH at which an enzyme-catalyzed reaction proceeds at the fastest rate.reactant – The substrate molecule that binds to and reacts with the enzyme.respiration – The series of reactions that release energy from glucose, in the presence of oxygen.
22 Boardworks GCSE Additional Science: Biology Name the structureBoardworks GCSE Additional Science: BiologyEnzymesTeacher notesThis activity could be used to check students’ understanding of the lock and key model.
23 Boardworks GCSE Additional Science: Biology Multiple-choice quizBoardworks GCSE Additional Science: BiologyEnzymesTeacher notesThis multiple-choice quiz could be used as a plenary activity to assess students’ understanding of enzymes. The questions can be skipped through without answering by pressing the forward arrow. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.