Enzyme Theory
This activity covers the lock and key hypothesis and enzyme activity. Enzymes like RNA polymerase are at the centre of most of the cells biochemical activity. This lesson answers the question, "How do enzymes work?" Students complete research, work with an online animation, make structured notes using a worksheet then test their knowledge with a range of questions including a data analysis.
Lesson Description
Guiding Questions
How does the random movement of particles help enzymes to function?
What is most important about the shape of an enzyme to enable it to catalyse reactions with its substrate?
In what way do simple diagrams of complex 3D enzyme structures help us to understand how enzymes work?
Activity 1 - How do enzymes work? (Lock and key hypothesis)
Watch the animation below which shows a simple model of enzyme function.
Short animation of the lock and key model from Ricochet Science
Summary of the main points about enzymes
Enzymes are proteins which work as biological catalysts.
They speed up the rate of a chemical reaction without themselves being changed.
The actual structure of enzymes is complex; they are often large proteins with a specific 3D shape.
The most important part of the shape on an enzyme is the active site.
The active site must fit the shape of the enzyme’s substrate.
The active site is where the substrate molecules bind and undergo a chemical reaction.
Each enzyme has a particular shape of active site. They can each only catalyse one specific reaction.
This is known as “enzyme-substrate specificity.”
Activity 2 - Structured questions about Enzymes
Complete the 
Enzyme worksheet which will help to make a record of important notes about enzymes.
Activity 3 - Measuring rates of reactions and identification of substrates of enzymes.
One of the easiest methods of measuring the rate of and enzyme catalysed reaction is to measure the amount of product produced by the reaction in a given time.
It is also possible to measure the time taken for the substrate to disappear.
In fact the best method of measuring the reaction rate usually depends on easiest way to measure a substrate or a product.
The rate of catalase activity is easily measured, without an indicator but using a measure of the volume of oxygen gas produced.
The rate of amylase is often measured using the disappearance of its substrate. Iodine indicator can identify the moment when all the starch has been hydrolysed.
Biologists often use experiments to study the rate of enzyme catalysed reactions.
This enzyme simulation from Jon Darkow in Ohio provides a great introduction to factors which affect enzyme reaction rates.
Click the link, and follow the steps below.
Follow the instructions in this box to carry out a simple activity using this simulation.
Answer the questions as you progress through each step.
Enzyme simulation questions
- Adjust each of the red "Initial" substrate sliders one at a time and identify which are the substrates of amylase and trypsin.
- Amylase catalyses a reaction with the substrate .................................................
- Trypsin catalyses reaction with the substrate ...................................................
- Describe the general relationship between substrate concentration and product concentration.
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- Reset the substrate sliders to 500 and move the temperature slider from side to side.
What is the optimum temperature of Amylase? ................................................
What is the optimum temperature of Trypsin? ................................................
What is the optimum temperature of taq DNA polymerase? ................................................
What is unusual about the optimum temperature of Taq polymerase
(Taq Polymerase is an enzyme found in the bacterium, T.aquaticus, living in hot springs?
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.....................................................................................................................................................Change the pH using the slider.
Use this to work out:The optimum pH of pepsin is ......................................
The optimum pH of Amylase is ....................................
The optimum pH of Trypsin is ......................................
The optimum pH of Taq polymerase is ........................
Use the lock and key hypothesis to explain in more detail why substrate concentration, temperature and pH affect the rate of enzyme catalysed reactions.
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Extension activities - Video and short online quiz about enzymes
Watch this short video introduction to university work on enzyme research from Birmingham University in the UK.
More information is available here.
Test yourselves using these multiple choice questions: Enzymes quiz 2.5
Teachers' notes
Many students will have experience of enzyme experiments but few seem to have a clear memory of how to speed up an enzyme controlled reaction, and what denaturing really is. These concepts are clearly addressed in this lesson.
Activity 1 is a revision of the lock and key model. It is important to note that this lesson is designed for SL students. The content has been carefully selected to cover the IB SL guide but not the extra HL details. This is so that SL students don't have to learn details which will not appear in the SL exam.
Pdf file of the Enzymes questions
HL students could save time by going directly onto the HL details of induced fit, and the extra details of the 3D structure of enzymes. This is shown in the animation in activity 1 but not mentioned.
Activity 2 is really about making nots about a topic which most students have studied before.
There are model answers to the enzyme's worksheet here:
Activity 3 incudes a simulation which could take students much further into working on rates of reactions. In this instance the questions are focused on the interactions between enzymes and their substrates, or the way that environmental variables affect the rate of reaction.
This animation might also be useful to see the molecular interactions between enzymes and their substrates, but it involves a file download: https://phet.colorado.edu/en/simulation/reactions-and-rates
This video from PDB does a great job of explaining the structure and function of enzymes. The graphics at the beginning show the molecules in the cytoplasm of the cell, it covers the activation energy and even the interactions between individual amino acid molecules in the catalysis of citrate to isocitrate.